13 Nov
2004
13 Nov
'04
3:43 p.m.
It's in excellent cosmetic condition. I powered it
up
You really should learn the basics about applying power to
electronic gear that has been off for some unknown period
of time.
It is an INCREDIBLY BAD idea to just go into a room full of
old computers and just randomly start applying power to equipment
in unknown condition. At an absolute minimum, you should check
the condition of the power supplies.
14 Nov
14 Nov
4:29 a.m.
On Sat, 2004-11-13 at 21:43 -0800, Al Kossow wrote:
I know that. Remember, I checked the PDP-7's power supplies
THOROUGHLY.
I checked capacitors on all the large supplies.
It's in
excellent cosmetic condition. I powered it up
You really should learn the basics about applying power to
electronic gear that has been off for some unknown period
of time.
It is an INCREDIBLY BAD idea to just go into a room full of
old computers and just randomly start applying power to equipment
in unknown condition. At an absolute minimum, you should check
the condition of the power supplies.
The Nord-10 had at least been powered up in
1993 (I found a system disk
backup with that date), and most likely later. The backup battery that
lets the CPU keep the contents of the memory and registers for a short
while actually contained a charge. I flipped that switch without
worrying the least bit.
Relax, I've got it all under contrJ;klj8977^%*&^
NO CARRIER
--
Tore S Bekkedal <toresbe(a)ifi.uio.no>
5:45 a.m.
It is an
INCREDIBLY BAD idea to just go into a room full of
old computers and just randomly start applying power to equipment
in unknown condition. At an absolute minimum, you should check
the condition of the power supplies.
The Nord-10 had at least been powered up in
1993 (I found a system disk
backup with that date), and most likely later. The backup battery that lets the CPU keep the contents of the memory and
registers for a short
while actually contained a charge. I flipped that switch without
worrying the least bit.
I would not be so reckless!. It only takes one failure in the PSU
regulator to take out most, if not all, of the chips in the machine (I
don't want to trust that crowbar protection will work!). I, alas, have
had it happen once, fortunately I could get all the chips and had adump
of the EPROM, but it was not a cheap experience. Running the PSUs on
dummy load and making sure the output voltages are correct is something
that I always do now.
-tony
6 a.m.
On Sun, 2004-11-14 at 19:45 +0000, Tony Duell wrote:
Which is 11 years ago.... At the very most 11 years ago, which still isn't
bad.
I think it suffices to say that the guy who cut his teeth on the machine
and has supported them since 1986, and *owned the company since 1992*
didn't have any problems with it... He said that the PSUs were sturdy
and had *plenty* of protection. They were used extensively in the
military and several railway backup systems, those things were
ruggedized to hell and back.
I may have been mistaken, but at the time, as presently, I didn't see
the need to delve deeper into the PSU.
--
Tore S Bekkedal <toresbe(a)ifi.uio.no>
It is an INCREDIBLY BAD idea to just go into a room
full of
old computers and just randomly start applying power to equipment
in unknown condition. At an absolute minimum, you should check
the condition of the power supplies.
The Nord-10 had at least been powered up in
1993 (I found a system disk
backup with that date), and most likely later. The backup battery that lets the CPU
keep the contents of the memory and registers for a short
while actually contained a charge. I flipped that switch without
worrying the least bit.
I would not be so reckless!. It only takes one failure in the PSU
regulator to take out most, if not all, of the chips in the machine (I
don't want to trust that crowbar protection will work!). I, alas, have
had it happen once, fortunately I could get all the chips and had adump
of the EPROM, but it was not a cheap experience. Running the PSUs on
dummy load and making sure the output voltages are correct is something
that I always do now.
-tony
9:13 a.m.
Which is 11
years ago....
At the very most 11 years ago, which still isn't bad. I think it suffices to say that the guy who cut his
teeth on the machine
and has supported them since 1986, and *owned the company since 1992*
didn't have any problems with it... He said that the PSUs were sturdy
That would not be enough for me. Heck, the assurance of the designer
wouldn't be enough for me (and nor, for that matter, would anybody else's
assurance). The risk is just too great.
Sure the PSU will have built-in protection -- all decent machines do
(although HP omitted it from their desktop calculators for some unknown
reason -- the HP9815, 9825, 9832, etc desparately need a crowbar!).But
I'd rather not rely on it. Better to be safe than sorry.
I may have been mistaken, but at the time, as
presently, I didn't see
the need to delve deeper into the PSU.
All you need to do is disconnect the PSU from the machine, connect it to
dummy loads (car bulbs are what I noramlly use -- 6V ones on the +5V
line, for example) and check the output voltages. You don't need to
investigate the internals of the PSU unless there's something wrong.
-tony
15 Nov
15 Nov
2:27 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
Testing power supplies before powering up a system is just plain paranoid! (And I'm
trying to be polite here!) There are a thousand parts in modern computers that can cause
just as much damage!!!!!!!! Just last week I THOROUGHLY tested a HP 1000 including
running test on ALL of the firmware ROMs (About three dozen of them!) plus CPU tests,
memory tests, PSU test etc etc etc. I'd had the machine running for several days
testing it. THEN I connected the Floating Point Unit (this was a F series HP 1000). As
soon I turned it on the internal memory tests started but it acted goofy. After removing
the FPU and further testing I found that the FPU had toasted the CPU card :-( It has one
bit in the Microcode section that's stuck high. I'm guessing it's a bus
transciever or something similar since the stuck bit appears in every memory location and
every register. (Anybody have schematics for the HP F-series CPU?)
Further example: YESTERDAY I was testing a "new" HP 1000 (an E-series this
time). A quick check of the PSU outputs showed it to be normal and we powered up the
computer, cleaned and reseated some cards, reconfigured some cards, installed other cards,
etc etc and powered it up and down numerous times over the course of several hours. THEN
it happened! The PSU started making a loud sizzling sound and poured out copious smoke!
All that testing and prior running gave no hint of the impending failure! What's
more, this is the SECOND time that I've had a HP 1000 PSU fail after running for over
an hour. FWIW I pulled the PSU out of another untested machine, put it in this one
(without testing it!) and everythings working again.
IF I had an absolutely unrepairable, irreplacceable computer and IF I had all the PSU
specs and pinouts it MIGHT justify the trouble of testing a PSU before using it to power
up a computer but otherwise forget it!
Joe
At 11:13 PM 11/14/04 +0000, you wrote:
I check the PSUs of machines that I own and have run before if I've not
powered them up for, say, a year oe more.... It doesn't take long to do
(especially not if you're familiar with the machine and/or have
schematics), putting right the damage can take a lot of time and money.
Most of the time you'll have no problems, sure. Most of the time when I
get a machine on the bench (wheter a 'new toy' or something from my
existing collection), the PSUs behave perfectly on dummy load. But if
something does got wrong, you really don't want to kill all the chips....
There is anotehr issue, actually. PSU problems -- marginally low
votlages, ripple, and so on, can cause all sorts of odd behaviour that
will take hours to find if you don't initially suspect the PSU (like the
time my PDP11/45 would run for 1botu an hour and a half before falling
over in all sorts of odd ways -- I traced that to a '+5V' supply to the
memory that was actually about +4.6V). Checking out the PSUs can
eliminate such problems.
Which is 11 years ago....
At the very most 11
years ago, which still isn't bad. I think it suffices to say that the guy who cut
his teeth on the machine
and has supported them since 1986, and *owned the company since 1992*
didn't have any problems with it... He said that the PSUs were sturdy
That would not be enough for me. Heck, the assurance of the designer
wouldn't be enough for me (and nor, for that matter, would anybody else's
assurance). The risk is just too great.
Sure the PSU will have built-in protection -- all decent machines do
(although HP omitted it from their desktop calculators for some unknown
reason -- the HP9815, 9825, 9832, etc desparately need a crowbar!).But
I'd rather not rely on it. Better to be safe than sorry.
I may have been mistaken, but at the time, as
presently, I didn't see
the need to delve deeper into the PSU.
All you need to do is disconnect the PSU from the machine, connect it to
dummy loads (car bulbs are what I noramlly use -- 6V ones on the +5V
line, for example) and check the output voltages. You don't need to
investigate the internals of the PSU unless there's something wrong.
-tony
4:11 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
>>>> "Joe" == Joe R
<rigdonj(a)cfl.rr.com> writes:
Joe> Testing power supplies before powering up a system is just plain
Joe> paranoid! (And I'm trying to be polite here!) There are a
Joe> thousand parts in modern computers that can cause just as much
Joe> damage!!!!!!!!
I disagree -- at least in the case of linear regulator supplies, which
is what you'll normally find in a classic computer.
A very simple and very nasty failure in a linear regulator is a short
in the pass transistor. If that happens, you get a much higher output
voltage, and there is no current limiting. It's a fair bet that this
will fry a large fraction of the semiconductors in your system.
If the supply has a "crowbar overvoltage protection" circuit in it,
that's a different matter. But testing a linear supply is trivial.
So why not do it?
If you let the magic smoke out of the computer, it's too late...
paul
4:53 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
On Mon, 2004-11-15 at 13:11 -0500, Paul Koning wrote:
I am for testing them in
some cases, like the PDP-7. I was without much
experience at the time, and with a machine of which 6 are known to
exist, I would MUCH rather err on the side of caution and spend a few
hours testing/reforming caps than watch the fireworks of computer
history.
>>>> "Joe" == Joe R <rigdonj(a)cfl.rr.com> writes:
Joe> Testing power supplies before powering up a system is just plain
Joe> paranoid! (And I'm trying to be polite here!) There are a
Joe> thousand parts in modern computers that can cause just as much
Joe> damage!!!!!!!!
I disagree -- at least in the case of linear regulator supplies, which
is what you'll normally find in a classic computer. If the supply has a "crowbar overvoltage
protection" circuit in it,
that's a different matter.
This PSU is rugged and has "Voltage OK"
lights on all the voltage lines.
It is according to a man who is knowing, incredibly sturdy and used with
defense systems all over the country.
But testing a linear supply is trivial.
So why not do it?
TRIVIAL? All the leads running into the PSU are *BOLTED* on two
large
bars labelled -5V and +5V. I had no tools at the time. The PSU itself is
inside the rack and there it will stay until I get it out, which I'm not
going to, because the thing is held in place by numerous screws and is
shit-heavy. If I got the screws loose, it would probably crash down on
the CPU.
If you let the magic smoke out of the computer, it's too late...
In this case,
no magic smoke as expected.
But access to a complete array of spares if nessecary. Oh, and the CPU
is built in TTL logic, so no hard-to-get spares. (Not that magic smoke
is *desirable*!)
I stand by my desicion to test the PDP-7, and not to test the Nord-10/S.
--
Tore S Bekkedal <toresbe(a)ifi.uio.no>
5 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
>>>> "Tore" == Tore S Bekkedal
<Tore> writes:
> If the supply has a "crowbar overvoltage
protection" circuit in
> it, that's a different matter.
Tore> This PSU is rugged and has
"Voltage OK" lights on all the
Tore> voltage lines. It is according to a man who is knowing,
Tore> incredibly sturdy and used with defense systems all over the
Tore> country.
"Incredibly sturdy" is nice. But that doesn't translate into "cannot
ever fail".
"Voltage ok" may mean there's a crowbar, or it may only mean there is
a voltage monitor. Those are very different things. Voltage monitors
wouldn't protect you against a regulator short.
Tore> But access to a complete array of spares if nessecary. Oh, and
Tore> the CPU is built in TTL logic, so no hard-to-get spares.
TTL is getting hard to find, especially the more obscure types such as
74S series. (And if the book says they want 74S, it's quite possible
no other variant will work...)
paul
10:11 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
"Voltage ok" may mean there's a crowbar,
or it may only mean there is
a voltage monitor. Those are very different things. Voltage monitors
I would suspect that latter, and not a particularly good monitor at that.
I've met PSUs where all the 'idiot lights' were on, but there were still
problems (excessive ripple on one of the outputs, for example).
wouldn't protect you against a regulator short.
Tore> But access to a complete array of spares if nessecary. Oh, and
Tore> the CPU is built in TTL logic, so no hard-to-get spares.
TTL is getting hard to find, especially the more obscure types such as
74S series. (And if the book says they want 74S, it's quite possible
no other variant will work...)
74S is trivial to find comparied with 74H (and yes I have found those in
classic computers) or 74L (not 74LS, of course) .Even some plain 74xxx
numbers are non-trivial to get now -- 74181 ALU, 7489 RAM, the fusible
link PROMs, 7456 and 7456 (mains - 1Hz dividers), etc, etc, etc. A look
through an old TTL databook will show a few dozen devices you'll no
longer see in the catalogues.
-tony
10:25 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
On Tue, Nov 16, 2004 at 12:11:19AM +0000, Tony Duell wrote:
74S is trivial to find comparied with 74H (and yes I
have found those in
classic computers) or 74L (not 74LS, of course)
I'd love to find a 74L00 for my Popular Electronics Elf... an 'LS00 works
fine in this design, of course, but the whole point was to be historically
accurate, and the article to add a 1861 _does_ list a 74L00.
The actual machine in question is not a classic, but the design certainly is.
-ethan
--
Ethan Dicks, A-130-S Current South Pole Weather at 16-Nov-2004 00:23 Z
South Pole Station
PSC 468 Box 400 Temp -33.4 F (-36.3 C) Windchill -59.2 F (-50.7 C)
APO AP 96598 Wind 10.2 kts Grid 060 Barometer 689.3 mb (10277. ft)
Ethan.Dicks(a)amanda.spole.gov http://penguincentral.com/penguincentral.html
11:07 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
In message <20041116002524.GA29431(a)bos7.spole.gov>
Ethan Dicks <dickset(a)amanda.spole.gov> wrote:
I'd love to find a 74L00 for my Popular
Electronics Elf... an 'LS00 works
fine in this design, of course, but the whole point was to be historically
accurate, and the article to add a 1861 _does_ list a 74L00.
The actual machine in question is not a classic, but the design certainly is.
By "Popular Electronics Elf", I assume you mean the COSMAC Elf? 256 bytes of
RAM, two HP hexadecimal LED displays (I used TIL311s instead), toggle-switch
data input and a CDP1802 CPU :)
I built one - nice little machine. Never really used it though.
Later.
--
Phil. | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem(a)philpem.me.uk | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.me.uk/ | 48xCD, ARCINv6c IDE, SCSI
... DOS Tip #3 : Don't use DOS.
1:27 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
TTL is getting hard to find, especially the more
obscure types such as
74S series. (And if the book says they want 74S, it's quite possible
no other variant will work...)
I do not think 74S is very hard to find (apart from the unprogrammed
PROMS, I suppose). Some of the 74L and 74H chips are getting difficult to
find, but these are the chips that never were popular (like the expanders
and AOI gates).
As a side note - does anyone know a source for ECL PALs (10K preferred
over 100K)? They were never popular either.
William Donzelli
aw288(a)osfn.org
3:02 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
PROMS, I suppose). Some of the 74L and 74H chips are
getting difficult to
find, but these are the chips that never were popular (like the expanders
and AOI gates).
Thay may not have been popular, but they were used. The HP98x0 processor
(bit-serial, 16 bit) has a 74H52 on one of the memory control boards as
the mux at one input to the ALU and a 74H54 with an expander (I forget
which, and I don't feel like grabbign the schematics) on the processor
data path PCB as the mux at the other ALU input. They do fail (the former
especially!).
-tony
9:41 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
Paul Koning wrote:
Tore> But access to a complete array of spares if
nessecary. Oh, and
Tore> the CPU is built in TTL logic, so no hard-to-get spares.
TTL is getting hard to find, especially the more obscure types such as
74S series. (And if the book says they want 74S, it's quite possible
no other variant will work...)
paul
I thought that 74F series parts were generally replacements for 74S
parts. Is this incorrect? A more serious concern is that the parts
that have been recently produced seem to be simpler glue logic, bus
transceivers, etc. Many of the nice functional blocks used for building
CPUs were dropped from manufacturers catalogs years ago, and many were
never even offered in the more recent logic families. Take, for
instance, the 74172, an 8x2 dual-ported register file used in the Data
General Nova 2.
--Bill
16 Nov
16 Nov
1:23 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
>>>> "William" == William Maddox
<wmaddox(a)pacbell.net> writes:
William> Paul Koning wrote:
Tore> But access to a complete array of spares if nessecary. Oh, and
Tore> the CPU is built in TTL logic, so no hard-to-get spares.
> TTL is getting hard to find, especially the more
obscure types
> such as 74S series. (And if the book says they want 74S, it's
> quite possible no other variant will work...)
>
> paul
William> I thought that 74F series parts were generally replacements
William> for 74S parts. Is this incorrect?
It depends.
Some designs depend on parts being "fast enough". Others are more
finicky. If they need "fast enough" then F or LS or ACT series logic
may well work. If they need "just right" then you have a potential
problem.
For example, some people have used 74S00 devices as crystal
oscillators. Those circuits are less likely to appreciate
substitution.
paul
7:04 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
William Maddox wrote:
I thought that 74F series parts were generally
replacements for 74S
parts. Is this incorrect? A more serious concern is that the parts
that have been recently produced seem to be simpler glue logic, bus
transceivers, etc. Many of the nice functional blocks used for building
CPUs were dropped from manufacturers catalogs years ago, and many were
never even offered in the more recent logic families. Take, for
instance, the 74172, an 8x2 dual-ported register file used in the Data
General Nova 2.
You can still GET that at http://www.unicornelectronics.com/ but just what
is stock on hand is all that is left. They have some 74S and 74H too.
Ben.
10:20 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
Paul Koning wrote:
'Generally' is right. 9 times out of 10 you can use 74F in place of 74S
(if the right function exists, which is by no means certain). The tenth
time, the F part is too fast, or causes too much ground bounce, or ...
-tony
Tore> But access to a complete array of
spares if nessecary. Oh, and
Tore> the CPU is built in TTL logic, so no hard-to-get spares.
TTL is getting hard to find, especially the more obscure types such as
74S series. (And if the book says they want 74S, it's quite possible
no other variant will work...)
paul
I thought that 74F series parts were generally replacements for 74S
parts. Is this incorrect? A more serious concern is that the parts
15 Nov
15 Nov
6:53 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration effort on the way!
At 01:11 PM 11/15/04 -0500, you wrote:
I disagree. Testing a power supply is far from trivial and merely reading the open
circuit voltage tells you virtually nothing. Power supplies need to be tested under load
(like batteries) and things like ripple and regulation need to be checked. In fact, you
can damage many PSUs by not having a suffient load on them. And without a load others will
go into overvoltage and trip the crowbar circuits and thus appear to be bad. That's
why I said that you need the specs for the supplies so you can be sure of having an
adaquete load to prevent damage (or know if they can be operated with no load) and what
the permissible regulation and ripple specs are as well as the current capacity. If you
don't know exactly what they're supposed to do, how do you think you can test
them? AND as I pointed out, I've had tested powers supplies fail TWICE just in the
last week after operating a short time so even if you do an adaquete test you can't be
sure that they won't fail in use.
AND we haven't even talked about how you're supposed to know such simple things
as the rated voltage outputs and pinouts of odd-ball things like the Nord that was being
discussed. Tell me, do YOU know what the outputs of the Nord PSU are supposed to be and
where the test points are???
>>>> "Joe" == Joe R <rigdonj(a)cfl.rr.com> writes:
Joe> Testing power supplies before powering up a system is just plain
Joe> paranoid! (And I'm trying to be polite here!) There are a
Joe> thousand parts in modern computers that can cause just as much
Joe> damage!!!!!!!!
I disagree -- at least in the case of linear regulator supplies, which
is what you'll normally find in a classic computer.
A very simple and very nasty failure in a linear regulator is a short
in the pass transistor. If that happens, you get a much higher output
voltage, and there is no current limiting. It's a fair bet that this
will fry a large fraction of the semiconductors in your system.
If the supply has a "crowbar overvoltage protection" circuit in it,
that's a different matter. But testing a linear supply is trivial.
So why not do it?
If you let the magic smoke out of the computer, it's too late...
And you can still let the smoke out even after days of testing as I pointed out in my
message. And that's based on an ACTUAL example and not some hypothetical discussion.
Joe
10:06 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
>>>> "Joe" == Joe R
<rigdonj(a)cfl.rr.com> writes:
Joe> Testing power supplies before powering up a system is just plain
Joe> paranoid! (And I'm trying to be polite here!) There are a
Joe> thousand parts in modern computers that can cause just as much
Joe> damage!!!!!!!!
I disagree -- at least in the case of linear regulator supplies, which
is what you'll normally find in a classic computer.
A very simple and very nasty failure in a linear regulator is a short
in the pass transistor. If that happens, you get a much higher output voltage, and there is no current limiting. It's a
fair bet that this
will fry a large fraction of the semiconductors in your system.
If the supply has a "crowbar overvoltage protection" circuit in it,
that's a different matter. But testing a linear supply is trivial.
So why not do it?
I'd rather not trust a protection device if I don't have to. Sure I like
crowbar circuits, and they have saved my chips a few times, but I don't
like to depend on them.
-tony
12:07 p.m.
New subject: Crowbar? (was: Re: Testing Power Supplies!)
Tony Duell wrote of crowbar protection circuits thus:
I'd rather not trust a protection device if I
don't have to. Sure I like
crowbar circuits, and they have saved my chips a few times, but I don't
like to depend on them.
Ah, twice in one week I get to expose my wanton ignorance. :) What
typically makes up a crowbar circuit? How are they triggered? If I'm
understanding this correctly, a crowbar quickly kills the PSU and then
drains power from the system rapidly and nondestructively... but how it
accomplishes this, or knows it _should_, I don't yet understand.
O'course, one could accomplish this with an actual crowbar applied
across the PSU output... but I suspect this would not be described as
"nondestructive". :)
-O.-
12:30 p.m.
New subject: Crowbar? (was: Re: Testing Power Supplies!)
At 06:07 PM 11/15/04 -0800, you wrote:
Tony Duell wrote of crowbar protection circuits thus:
A crowbar is a very simple yet effective circuit to prevent PSUs from outputing
excessive voltage. It's nothing more than a SCR (Silicon Controlled Rectifier) across
the PSU output and a zener diode from the gate of the SCR to ground (and a small resistor
to supply a small amount of current to the gate-zener junction). The zener sets the trip
voltage of the SCR. The resistor-zener combination forms a small constant voltage source
that is applied to the SCR gate. Anytime the PSU output exceeds the zener voltage (plus
the gate voltage of the SCR) the SCR fires and becomes a dead short (minus a fraction of a
volt due to the SCR PN junction) and the PSU output is shorted out. Once the SCR fires it
says on regardless of the trigger voltage. The only way to remove the short is to turn off
power to the PSU and let it discharge and then reapply power. As you might have guessed
these circuits are very fast since they're so simple and they're located right on
the PSU output. The FAST response and nearly dead short account for the name
"crowbar". It has the effect similar to that of throwing a metal crowbar right
across the PSU output.
And yes the PSU had better be able to handle the almost dead short or have a fuse or
circuit breaker in it or something is going to give!
Joe
I'd rather not trust a protection device if I
don't have to. Sure I like
crowbar circuits, and they have saved my chips a few times, but I don't
like to depend on them.
Ah, twice in one week I get to expose my wanton ignorance. :) What
typically makes up a crowbar circuit? How are they triggered? If I'm
understanding this correctly, a crowbar quickly kills the PSU and then
drains power from the system rapidly and nondestructively... but how it
accomplishes this, or knows it _should_, I don't yet understand.
O'course, one could accomplish this with an actual crowbar applied
across the PSU output... but I suspect this would not be described as
"nondestructive". :)
-O.-
2:56 p.m.
New subject: Crowbar? (was: Re: Testing Power Supplies!)
Tony Duell wrote of crowbar protection circuits thus:
CLose :-). The idea is to be non-destructive to the rest of the machine,
even if it ends up destroying parts of the defective PSU. You want to
short-circuit the PSU outputs (normally only the +5V output) if it goes
overvoltage. Typically the circuit is something like :
-------------+-----------------------+--------------------o +5V
| |
----- |
5V1 zener ^ | |
/ | \ |
| |
| \ | /
+--------------------\ V SCR
| --------
| |
/ |
\ |
100 Ohm / |
\ |
| |
--------------+-----------------------+-------------------o oV
If the 5V rail goes overvoltage, the zener breaks down and turns on the
SCR which short-circuits the 5V rail (and carries on shorting it until
the PSU output current drops to close to zero).
-tony
I'd rather not trust a protection device if I
don't have to. Sure I like
crowbar circuits, and they have saved my chips a few times, but I don't
like to depend on them.
Ah, twice in one week I get to expose my wanton ignorance. :) What
typically makes up a crowbar circuit? How are they triggered? If I'm
understanding this correctly, a crowbar quickly kills the PSU and then
drains power from the system rapidly and nondestructively... but how it
accomplishes this, or knows it _should_, I don't yet understand.
O'course, one could accomplish this with an actual crowbar applied
across the PSU output... but I suspect this would not be described as
"nondestructive". :)
10:03 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
Testing power supplies before powering up a system is just plain
paranoid! (And I'm trying to be polite here!) There are a thousand parts
Nad anyone who doesn't do so is just plain clueless (and I am being
_very_ poilite) here. I've seen (and had to repair) the damage caused by
a wayward PSU...
Some PSUs have no overvoltage protection at all. Top of that list is the
HP9815, 9825, 9831, 9877, etc. If the 5V chopper shorts in one of those
(and it does quite often) you can bet you'll be replacing every chip in
the machine, just about. The 9815 is a particularly nasty one since the
PSU can't be disconnecte from everything else, but at least you can
remove the CPU and kayboard/display PCBs, the tape drive, and unplug the
printhead (which is a custom hybrid circuit). Then all that dies if the
PSU is faulty are a few TTL chips on the PSU/interface board.
Next on the list are the Bozchert 2-stage switchers. These have a
non-isolated switching regulator to bring the 350V (rectified mains) down
to about 150V, which then feeds a free-running oscillator driving the
chopper transformer. Regulation is applied to the first regulator stage.
If that first chopper shorts, the output rails all jump to about double
what they should be. You hope the crowbar fires, but then the overcurrent
trip on the primary side doesn't do anything (it works on the first
regulator, which is shorted), so you hope that the fuse or the second
choppers fail befor the crowbar SCR. Normally they do, but...
And I am sure I've come across a device (I don't think it was a computer
per se) where the PSU outputs lept to the unregulated input voltages
(less the saturation voltage of the pass transsitors) if the PSU control
PCB was removed. You're talking about a second-hand machine here, no idea
what board have been 'borrowed'...
in modern computers that can cause just as much
damage!!!!!!!! Just
Name one other failure that will take out every chip in the machine.
location and every register. (Anybody have schematics
for the HP
F-series CPU?)
Trace them out yourself. I've done it for lots of HP devices...
happened! The PSU started making a loud sizzling
sound and poured out
copious smoke! All that testing and prior running gave no hint of the
impending failure! What's more, this is the SECOND time that I've had a
HP 1000 PSU fail after running for over an hour. FWIW I pulled the PSU
That sounds like a PSU that needs to be run on a soak test fro quite a
time, then...
out of another untested machine, put it in this one
(without testing
it!) and everythings working again.
IF I had an absolutely unrepairable, irreplacceable computer and IF
IMHO _all_ classic computers are irreplaceable!
I had all the PSU specs and pinouts it MIGHT justify
the trouble of
Powering up machines without having read and understood the technical
manual/schematics is a second moan of mine, but...
testing a PSU before using it to power up a computer
but otherwise
forget it!
It takes about 5 minutes to test a PUS on dummy load. No longer. It's
_always_ worth doing.
-tony
11 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
Rumor has it that Tony Duell may have mentioned these words:
Stick o'Dynomite.[1]
Well, you *asked*! ;-)
Laterz,
Roger "Merch" Merchberger
[1] and it's certainly more fun than testing PSUs.
--
Roger "Merch" Merchberger -- SysAdmin, Iceberg Computers
zmerch(a)30below.com
Hi! I am a .signature virus. Copy me into your .signature to join in!
in modern
computers that can cause just as much damage!!!!!!!! Just
Name one other failure that will take out every chip in the machine. 
12:17 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
> > in modern computers that can cause just as
much damage!!!!!!!! Just
>Name one other failure that will take out every chip in the machine.
On Mon, 15
Nov 2004, Roger Merchberger wrote:
Stick o'Dynomite.[1]
Well, you *asked*! ;-)
or a college administration.
12:31 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
At 06:17 PM 11/15/04 -0800, you wrote:
Or a crew of Pakistani maintenance workers!
> > in
modern computers that can cause just as much damage!!!!!!!! Just
>Name one other failure that will take out every chip in the machine.
On Mon, 15
Nov 2004, Roger Merchberger wrote:
Stick o'Dynomite.[1]
Well, you *asked*! ;-)
or a college administration.
2:51 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
Rumor has it that Tony Duell may have mentioned these words:
Stick o'Dynomite.[1]
Well, you *asked*! ;-)
That is not a _failure_ :-)
-tony
in modern
computers that can cause just as much damage!!!!!!!! Just
Name one other failure that will take out every chip in the machine. 
9:46 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
On Mon, 2004-11-15 at 20:00 -0500, Roger Merchberger wrote:
Rumor has it that Tony Duell may have mentioned these
words:
Stick o'Dynomite.[1]
Ahh, that requires outside help though and so doesn't count :)
Unattended fire would probably do a nice job - PCBs burn pretty well
when they get hot enough.
I've only ever seen a real spontaneous fire in a monitor though, not in
a system unit. It's probably possible if there's enough dust and
something gets hot enough though.
in modern
computers that can cause just as much damage!!!!!!!! Just
Name one other failure that will take out every chip in the machine. Hi! I am a .signature virus. Copy me into your
.signature to join in!
Heh, I'm going to have to steal that one - I like it :)
J.
--
PERSON 1: That's an awful gash on your forehead! How did you get it?
PERSON 2: I bit myself.
PERSON 1: How the hell did you manage to bite yourself on the forehead?
PERSON 2: I stood on a chair.
16 Nov
16 Nov
10:22 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
I've only ever seen a real spontaneous fire in a
monitor though, not in
a system unit. It's probably possible if there's enough dust and
something gets hot enough though.
I've had an RK05, or more precisely the blower fan, catch fire. Being a
good, solid, DEC device it carried on working with flames visible through
the front window (!). I retraced the heads, shut the system down, and
fortunately the flames went out. It turned out to be insulation breakdown
in the fan motor windings.
A friend of mine gave me anothe defective RK05 blowwer, this one with bad
bearings, and using parts of each I got the drive running again.
-tony
15 Nov
15 Nov
4:16 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
It takes about 5 minutes to test a PUS on dummy load.
No longer.
...if you have Tony Duell's workshop and tools available.
I, for example, have few suitable dummy loads at hand. I have a load
resistor which came form an old Sun (4 ohms), though I'm not sure
whether it's between 5V and ground or 12V and ground - it I suspect the
latter, since it looks more like 36W than 6?W. (It could even be
between 5V and 12V from what I can tell, though that would be Weird.)
I actually do not even have a reliable voltmeter, much less the
properly working oscilloscope I'd want to check things like ripple.
Of course, I also generally work with machines that, while classic
according to our definition, are not nearly as priceless as, say, a
Norsk Data 10/S; they tend to be more like SPARCstation IPXen. (Thus,
both less likely to have a fried PSU and less damage done if so.)
/~\ The ASCII der Mouse
\ / Ribbon Campaign
X Against HTML mouse(a)rodents.montreal.qc.ca
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
9:28 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
At 01:16 AM 11/16/2004, you wrote:
I, for example, have few suitable dummy loads at hand.
I have a load
resistor which came form an old Sun (4 ohms), though I'm not sure
whether it's between 5V and ground or 12V and ground - it I suspect the
latter, since it looks more like 36W than 6?W. (It could even be
between 5V and 12V from what I can tell, though that would be Weird.)
I actually do not even have a reliable voltmeter, much less the
properly working oscilloscope I'd want to check things like ripple.
Old disk drives, if they'll at least spin up, make good dummy loads.
The AC setting on a voltmeter will let you know if you have too much ripple
on a DC supply.
Ed K.
16 Nov
16 Nov
1:25 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
> I, for example, have few suitable dummy loads at
hand. I have a
> load resistor which came form an old Sun (4 ohms), though I'm not
> sure whether it's between 5V and ground or 12V and ground - it I
> suspect the latter, since it looks more like 36W than 6??W. (It
> could even be between 5V and 12V from what I can tell, though that
> would be Weird.)
>
> I actually do not even have a reliable voltmeter, much less the
> properly working oscilloscope I'd want to check things like
> ripple.
Ed> Old disk drives, if they'll at least spin up, make good dummy
Ed> loads. The AC setting on a voltmeter will let you know if you
Ed> have too much ripple on a DC supply.
Depends on the voltmeter...
Actually, a resistor is a classic dummy load. They have the advantage
of being dirt cheap, and readily available in thousands of
variations. If Radio Shack doesn't hack it, Digikey certainly will.
Ok, it's not so easy for Ethan...
paul
2:15 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
At 10:25 AM 11/16/2004, you wrote:
Ed> Old disk drives, if they'll at least spin
up, make good dummy
Ed> loads. The AC setting on a voltmeter will let you know if you
Ed> have too much ripple on a DC supply.
Depends on the voltmeter...
Actually, a resistor is a classic dummy load. They have the advantage
of being dirt cheap, and readily available in thousands of
variations. If Radio Shack doesn't hack it, Digikey certainly will.
Yup!
Well, for +12 and +5 you'll need two resistors though.
Power rating? [time spent pondering] 12v 1A = 12w, 5v 1A = 5w should do it.
Ooops, no 12 ohm or 5 ohm power resistors, got a bunch of 1 ohm ones,
so I can series/parallel a bunch of them ....
Screw it, they're not that much, maybe a couple of buck each.
Then connectors (what's the Molex part number?), and wires and heat shrink
and solder,
maybe a perf board to hold them, or a minibox
[project creep occurs, more features, more time, more money, CCTALK piles up]
then shipping expense (and time) from Digikey, or gas and AGGREVATION going
to RadioShack
["No, I already have a cell phone and Internet thanks, where are the
components, way in the back?"
then a wait at checkout as Granny gets a new hearing aid battery]
Maybe $10-$20 bucks,
Ooops, got to go back for the terminal lugs I forgot, or DigiKey was out of
stock on.
Vs.
Pull old XT2190 or ST251 from junk box,
plug in power supply lead, done.
Cost = 0, time = 1 minute, satisfaction at not having to go through above
nonsense = priceless!
(plus giving more time to keep up with CCTALK email and for composing
thoughtful email responses like this one! <g>).
:-)
I got an ATX power supply tester a few months back after a rash of bad ATX
power supplies.
Very handy.
Thought one for AT type power supplies would be good too.
Hey, just a few resistors for +12, +5 and some LEDS's, no sweat.
STILL working on it, or rather it's still not been done.
Got a box full of junk MFM drives, they work fine for this.
PLUS! the inductive loads and relay kicks from old drives might be better
than resistors anyway [thereby breathing more life into this thread].
Ed K.
2:41 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
At 11:15 AM 11/16/04 -0500, you wrote:
At 10:25 AM 11/16/2004, you wrote:
OK I just picked up some computers with 150 Amp 5 volt supplies. Now figure out the
necessary resistrance and wattage and go find me a resistor :-)
Joe
Ed> Old disk drives, if they'll at least
spin up, make good dummy
Ed> loads. The AC setting on a voltmeter will let you know if you
Ed> have too much ripple on a DC supply.
Depends on the voltmeter...
Actually, a resistor is a classic dummy load. They have the advantage
of being dirt cheap, and readily available in thousands of
variations. If Radio Shack doesn't hack it, Digikey certainly will.
Yup!
Well, for +12 and +5 you'll need two resistors though.
Power rating? [time spent pondering] 12v 1A = 12w, 5v 1A = 5w should do it. Ooops, no 12 ohm or 5 ohm power resistors, got a bunch
of 1 ohm ones,
so I can series/parallel a bunch of them ....
Screw it, they're not that much, maybe a couple of buck each.
Then connectors (what's the Molex part number?), and wires and heat shrink
and solder,
maybe a perf board to hold them, or a minibox
[project creep occurs, more features, more time, more money, CCTALK piles up]
then shipping expense (and time) from Digikey, or gas and AGGREVATION going
to RadioShack
["No, I already have a cell phone and Internet thanks, where are the
components, way in the back?"
then a wait at checkout as Granny gets a new hearing aid battery]
Maybe $10-$20 bucks,
Ooops, got to go back for the terminal lugs I forgot, or DigiKey was out of
stock on.
Vs.
Pull old XT2190 or ST251 from junk box,
plug in power supply lead, done.
Cost = 0, time = 1 minute, satisfaction at not having to go through above
nonsense = priceless!
(plus giving more time to keep up with CCTALK email and for composing
thoughtful email responses like this one! <g>).
:-)
I got an ATX power supply tester a few months back after a rash of bad ATX
power supplies.
Very handy.
Thought one for AT type power supplies would be good too.
Hey, just a few resistors for +12, +5 and some LEDS's, no sweat.
STILL working on it, or rather it's still not been done.
Got a box full of junk MFM drives, they work fine for this.
PLUS! the inductive loads and relay kicks from old drives might be better
than resistors anyway [thereby breathing more life into this thread].
Ed K.
3:34 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
On Tue, 16 Nov 2004, Joe R. wrote:
OK I just picked up some computers with 150 Amp 5
volt supplies. Now
figure out the necessary resistrance and wattage and go find me a
resistor :-)
Oh NO!! not (gasp!) OHM'S LAWWWW......
Lessee - 5 times 150 is, um... 14.2 carry the three decimal 05,
differentiating and simplifying - square root of of the product modulo
3.14159265.... ummmm....
oh yeah! 750 watts, give or take a microjoule.
Okay, now 750 watts (plus/minus a microjoule) at 5 volts DC potential
is...
[see procedure above, substituting dV/dT for all occurences of Zeta]
ah, yes: 0.03333 ohms, but you could use a .1 1Kw unit and be fine.
This is assuming you want to test the power supply at close to full
load. If you just want to see if it puts out current, then a smaller
resistor, say .5 ohm, 200 W would do, if you limited the duration of the
test so as not to fry the load.
Actually for loads like this, a bucket of salt water with a couple of
heavy metal bars dunked it it, connected to the PS, would also work -
using an ammeter, vary the distance between the bars until the PS is
putting it's rated current into the load.
Also makes a nice amount of hydrogen and other interesting gasses.
Cheers
John
10:30 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
OK I just picked up some computers with 150 Amp 5
volt supplies. Now
figure out the necessary resistrance and wattage and go find me a
resistor :-)
Now what I'd do there is very simple...
6V car headlamp bulbs tend to have 36W filaments, and double-dippers with
2 36W filaments are not uncommon. For short periods (like testing PSUs)
you could run both filaments together. And light bulbs approximate to
constant current devices, so I would guess they'd take 6A (each filament)
from a 5V supply too. Or thereabouts.
I'd normally test a PSU at around half its rated current, so around 75A.
Each bulb (both filaments) takes 12A, so use half a dozen of them. And
yes I do keep such bulbs in stock for testing such PSUs (my I2S image
processors have such a PSU module for each crate...)
-tony
11:57 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
Ok for the ones of you that didn't get it I was being sarcastic. That's why the
smiley at the end of the message. I just wondered what the reaction to trying to find a
.0333 Ohm 750 Watt resistor would be. FWIW I once made such a resistor out of paralleled
incandescent heaters when I was in a small town in Virginia that didn't have anything
other than a small town hardware store. IIRC it took about ten or eleven heaters in
parallel to get a low enough resistance.
Incandesent bulbs are a good idea but you have to be careful. Their resistance
isn't linear and varies widely depending on the voltage. That makes them dammed
difficult to use accurately. The same applies to the heaters that I used but luckly I had
a GOOD ampmeter and voltmeter.
Joe
At 12:30 AM 11/17/04 +0000, you wrote:
OK I just
picked up some computers with 150 Amp 5 volt supplies. Now
figure out the necessary resistrance and wattage and go find me a
resistor :-)
Now what I'd do there is very simple...
6V car headlamp bulbs tend to have 36W filaments, and double-dippers with
2 36W filaments are not uncommon. For short periods (like testing PSUs)
you could run both filaments together. And light bulbs approximate to
constant current devices, so I would guess they'd take 6A (each filament)
from a 5V supply too. Or thereabouts.
I'd normally test a PSU at around half its rated current, so around 75A.
Each bulb (both filaments) takes 12A, so use half a dozen of them. And
yes I do keep such bulbs in stock for testing such PSUs (my I2S image
processors have such a PSU module for each crate...)
-tony
17 Nov
17 Nov
3:04 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
>>>> "Joe" == Joe R
<rigdonj(a)cfl.rr.com> writes:
Joe> Ok for the ones of you that didn't get it I was being
Joe> sarcastic. That's why the smiley at the end of the message. I
Joe> just wondered what the reaction to trying to find a .0333 Ohm
Joe> 750 Watt resistor would be.
A nice way to make high power resistors is to take low power resistors
and dunk them in water. For example, a pair of 1 watt 100 ohm
resistors in parallel, in water, makes an excellent 100 watt dummy
load for ham radio applications. If you run it for a long stretch you
get steam, but the resistors stay healthy.
For a 33 milliohm resistor, I might consider a suitable length of
ordinary 20 gauge home electric wire, insulated, in water. That wire
is rated for 20 amps in conduit, probably closer to 30 in open air, so
750 watts in water wouldn't be an unreasonable thing to do.
paul
1:34 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
Tony Duell wrote:
6V car headlamp bulbs tend to have 36W filaments, and double-dippers with
...
I'd normally test a PSU at around half its rated
current, so around 75A.
Each bulb (both filaments) takes 12A, so use half a dozen of them. And
huh. I use them to limit current when charging new motorcycle batteries
but i never concidered using them to load a supply.
thats a *really* good idea... thanks!
(and it has the added advantage of an analog output :-)
-brad
16 Nov
16 Nov
10:19 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
The AC setting on a voltmeter will let you know if you
have too much ripp=
le=20
on a DC supply.
That depends very much on the voltmeter!. Most of the ones I have here
simply use a rectifier on the AC ranges so that the meter responds to
either the peak or the mean of the absolute value of the input signal,
with a suitable scalling correciton so the actual reading is the RMS
value assuming a sine wave input.
They will quite happily indicate (and mis-read the value of, of course) a
DC input when set to AC,.
-tony
15 Nov
15 Nov
9:42 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
On Tue, 2004-11-16 at 01:16 -0500, der Mouse wrote:
I believe some PSU's need the load between 5V and ground, others between
12V and ground (or some other rail), depending on the design of the PSU.
I tend to use an old scrap hard drive as a dummy load for PSU's with 5V
and 12V rails (plus it gives an audible sound that something's
happening :)
cheers
Jules
It takes about
5 minutes to test a PUS on dummy load. No longer.
...if you have Tony Duell's workshop and tools available.
I, for example, have few suitable dummy loads at hand. I have a load
resistor which came form an old Sun (4 ohms), though I'm not sure
whether it's between 5V and ground or 12V and ground - it I suspect the
latter, since it looks more like 36W than 6?W. (It could even be
between 5V and 12V from what I can tell, though that would be Weird.)
16 Nov
16 Nov
10:16 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
It takes about 5 minutes to test a PUS on dummy
load. No longer.
...if you have Tony Duell's workshop and tools available.
I, for example, have few suitable dummy loads at hand. I have a load
resistor which came form an old Sun (4 ohms), though I'm not sure
whether it's between 5V and ground or 12V and ground - it I suspect the
latter, since it looks more like 36W than 6=BCW. (It could even be
between 5V and 12V from what I can tell, though that would be Weird.)
I would be _very_ suprised if it was the last of those!
I actually do not even have a reliable voltmeter, much less the
properly working oscilloscope I'd want to check things like ripple.
However, I am not sure I'm happy with that. Most hobbies require you to
have some equipment, and IMHO a basic toolkit, basic test gear (which
would include a good multimeter and probably a 'scope), some
special-purpose units, etc are essential for classic computing.
Rmemebr that most computers run off 5V and maybe 12V. You don't need that
many dummy loads!. An assortment of car bulbs (and holders if you don't
want to solder wires driectly to the bulb caps) is a good start.
-tony
4:16 p.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
I actually do
not even have a reliable voltmeter, much less the
properly working oscilloscope I'd want to check things like ripple.
However, I
am not sure I'm happy with that.
17 Nov
17 Nov
7 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
Tony Duell wrote:
:-)
That is only true about TTL and computers that used a Z80 or later designed
chips.
It takes about 5 minutes to test a PUS on dummy load.
No longer.
...if you have Tony Duell's workshop and tools available. I, for example, have few suitable dummy loads at
hand. I have a load
resistor which came form an old Sun (4 ohms), though I'm no
Rmemebr that most
computers run off 5V and maybe 12V. You don't need that
many dummy loads!. An assortment of car bulbs (and holders if you don't
want to solder wires driectly to the bulb caps) is a good start. -tony
.
9:19 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
Rmemebr that
most computers run off 5V and maybe 12V. You don't need that
many dummy loads!. An assortment of car bulbs (and holders if you don't
want to solder wires driectly to the bulb caps) is a good start.
That is only true about TTL and computers that used a Z80 or later designed
chips.
11:23 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
>>>> "Tony" == Tony Duell
<ard(a)p850ug1.demon.co.uk> writes:
> > Rmemebr that most computers run off 5V and
maybe 12V. You don't
> need that > many dummy loads!. An assortment of car bulbs (and
> holders if you don't > want to solder wires driectly to the bulb
> caps) is a good start.
>
> That is only true about TTL and computers that used a Z80 or later
> designed chips.
Tony> DTL also uses +5V IIRC.
I believe +6, though +5 would probably work.
And RTL is +3.6...
paul
16 Nov
16 Nov
4:25 a.m.
New subject: Testing Power Supplies! Re: Norsk Data Nord-10/S restoration
This thread is turning into one of those ...
* Sometimes you really need to, sometimes you don't.
* Powered up 10 years ago means it's probably OK, if the thing was NEW
10 years ago; if it was old then it's ancient now.
* That said, testing is "easy" on ferroresonant S100 chassis
and hard on smart-ass switchers with fixed loads; you need OEM
data to test.
I think a good rule of thumb is, you need to know when to test,
and when you might reasonably 'get away without it'.
As always, knowledge, information and luck is required, and we
all make judgement calls, right and wrong.
7341
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