21 Apr
2009
21 Apr
'09
12:09 a.m.
Some of the smoke came out of my Osborne 1 this weekend. It doesn't
appear to have been fatal, as it was still functioning when I cut the
power. I'm giving the CRT some time to fully discharge before I open
it up, probably next weekend. It was probably a failing capacitor,
although it didn't explode, it merely got really warm over a period of
hours. But since there are some similar machines that I haven't
recently used, this question came to mind.
I've used the variac technique to reform capacitors, but thus far
haven't done this on a machine that contains a CRT because I don't
know what the reduced voltage is going to do to the CRT. The next
machine to power up on my list is a Compucolor II. Dare I power it at
15 volts for a few days before starting the slow ramp up to 115? Or
do I need to go in and detach the CRT circuitry before I try anything
like that.?
21 Apr
21 Apr
1 a.m.
On 20 Apr 2009 at 17:09, Eric J Korpela wrote:
I've used the variac technique to reform
capacitors, but thus far
haven't done this on a machine that contains a CRT because I don't
know what the reduced voltage is going to do to the CRT. The next
machine to power up on my list is a Compucolor II. Dare I power it at
15 volts for a few days before starting the slow ramp up to 115? Or
do I need to go in and detach the CRT circuitry before I try anything
like that.?
While it may do some good to reform oil capacitors, has anyone had
any solid information indicating that a slow ramp-up on more-or-less
modern electrolytics does much good? Do marginal caps treated this
way continue to give reliable service, or is one just putting off the
inevitable?
I'm more of the "duck and plug" mindset myself.
Chuck
1:19 a.m.
On Mon, Apr 20, 2009 at 6:00 PM, Chuck Guzis <cclist at sydex.com> wrote:
While it may do some good to reform oil capacitors,
has anyone had
any solid information indicating that a slow ramp-up on more-or-less
modern electrolytics does much good?
I've wondered this myself. I've also wondered what a suitable
definition of modern is. I've had capacitors explode on sudden power
application. I've never had one explode on a slow ramp with a variac,
but I've had them warm up. I've also seen DC current decrease over
the course of several hours when applying low DC voltages to boards,
but I've never been able to confirm the same with a variac.
I'm more of the "duck and plug" mindset
myself.
Again, with a CRT in the mix, I worry about the damage an exploding
capacitor can do.
Eric
1:45 a.m.
Again, with a CRT in the mix, I worry about the damage
an exploding
capacitor can do.
Eric
That's not the concern you need to be having. The concern is that
turning on a CRT too slowly is going to burn out its power supply and
possibly other B+ components... especially if it uses an SMPS.
If you're not going to do the work of properly testing/replacing the
caps prior to power on, then just use the routine I use when being lazy
or otherwise in a hurry:
- with a variac set to 20V, and your device on, turn the variac on and
quickly turn it from 20V to 90V. This is fast enough to prevent a CRT
PSU blowout due to excessive current from low voltage... and gives you a
soft start in case of marginal components.
- Work your way from 90 to whatever in 5V increments every 15 minutes...
turning slowly.
That's the about the best you can do with a variac alone.. on a CRT.
The chief drawback to the Variac is that you're not in charge of the
current... only the voltage. Current control AND voltage control is
what you need for caps reforming... AGAIN -- if there's any benefit to
be had from caps reforming... which is doubtful.
Caps the smaller they are the more just plain dried out they are! No
amount of reforming will change that.
jS
1:03 a.m.
You can't "variac" any device that uses a switchmode power supply.
You'll need to go through and test each cap in the machine, taken apart.
Proper reforming (assuming any of the caps even need reforming) by
variac alone is extremely tedious to do.. and probably not even possible
especially if you're attempting to variac an entire machine at once.
A variac is far better employed to just give your devices a "soft
start." Quickly turn the voltage from 0 to 110V, then slower to its
normal voltage. This is better than an instant-on, at least.
Electrolytic forming can be maintained by occasionally applying working
voltage to the cap. How often it's needed depends on capacitor
manufacturer and particular production run (due to varying rates of
oxide breakdown).
But for all practical purposes, if a device is powered up every 1-3
("several") years for 30-60 minutes, the capacitors should not fail from
lack of forming. They'll still fail from other reasons -- like drying out.
Capacitors instead of exploding more often just slowly become less
effective.
Re hot caps: a cap that gets hot should be replaced. Excessive leakage
and/or too high an ESR is causing too much (DC or AC, respectively)
power to be dissipated in the capacitor.
Eric J Korpela wrote:
Some of the smoke came out of my Osborne 1 this
weekend. It doesn't
appear to have been fatal, as it was still functioning when I cut the
power. I'm giving the CRT some time to fully discharge before I open
it up, probably next weekend. It was probably a failing capacitor,
although it didn't explode, it merely got really warm over a period of
hours. But since there are some similar machines that I haven't
recently used, this question came to mind.
I've used the variac technique to reform capacitors, but thus far
haven't done this on a machine that contains a CRT because I don't
know what the reduced voltage is going to do to the CRT. The next
machine to power up on my list is a Compucolor II. Dare I power it at
15 volts for a few days before starting the slow ramp up to 115? Or
do I need to go in and detach the CRT circuitry before I try anything
like that.?
1:29 a.m.
On Mon, Apr 20, 2009 at 6:03 PM, js at cimmeri.com <js at cimmeri.com> wrote:
You can't "variac" any device that uses a switchmode power supply.
?You'll
need to go through and test each cap in the machine, taken apart.
I'm aware of that. Unless I've forgotten something, no switching
supply is involved in these machines. Unless the supply that provides
HV to the CRT is a switcher. That's one of the reasons I ask. I'm
not too familiar with the guts of a CRT.
Proper reforming (assuming any of the caps even need
reforming) by variac
alone is extremely tedious to do.. and probably not even possible especially
if you're attempting to variac an entire machine at once.
Yes, it takes weeks to get to operating voltage. I'm not sure it
really counts as tedious, when most of what is involved is tweaking a
knob daily and checking for heat or smoke. Voltage and/or current
monitors would be nice, but who's got a working chart recorder these
days? I suppose I could turn an old laptop into one.
Eric
1:43 a.m.
Eric J Korpela wrote:
Yes, it takes weeks to get to operating voltage.
I'm not sure it
really counts as tedious, when most of what is involved is tweaking a
knob daily and checking for heat or smoke.
http://www.brouhaha.com/~eric/software/wrec/
2:41 a.m.
I'm aware of that. Unless I've forgotten
something, no switching
supply is involved in these machines. Unless the supply that provides
HV to the CRT is a switcher. That's one of the reasons I ask. I'm
not too familiar with the guts of a CRT.
The HV portion is really a Tesla coil using the horizontal oscillator
for frequency input... and as far as I know would not be hurt by the
lower voltage. Rather, it's the main power supply that might be.
Yes, it takes weeks to get to operating voltage.
I'm not sure it
really counts as tedious, when most of what is involved is tweaking a
knob daily and checking for heat or smoke. Voltage and/or current
monitors would be nice, but who's got a working chart recorder these
days? I suppose I could turn an old laptop into one.
Well, that's excessive. It only takes, at most, a few hours to reform
the kinds of caps we're bound to encounter in these machines... as one
guy pointed out here a few weeks back.. this isn't vintage audio... and
without current limiting, it's an awfully crude method because IF
reformation is needed in any particular cap, and IF you raise the
voltage too fast anywhere along the way, excessive current is going to
give you pinholes in your cap's foil.
I want to stress again that if machines are powered on every several
years for a few hours, your oxide layer isn't going to be your main
concern... because that is one area where modern caps are superior....
Rather, your main concern is going to be dried out caps resulting from
excessive heat or just age.
Caps aging is a multivariable problem... and you really have to assess
your particular piece of equipment for all those variables before
proceeding on any kind of cap maintenance, testing, or replacement protocol.
jS
Eric
4:40 a.m.
While we're giving electrolytic caps another go-round, here's another angle on
(modern) electrolytic caps:
I was repairing an HP 9815 (desktop programmable calc) a month ago. While
tracing it out to make the schematic, I noticed that a 680 uF, 25V electrolytic
cap for the +15V supply filter had been installed backwards (reversed
polarity). This was not a replacement or earlier repair, it came out of the
factory this way in 1975 (even HP screws up on occasion).
Granted that it's on the output of the regulator so it's not as critical as if
it were the main smoothing cap right after the rectifiers, but it was
nonetheless interesting that the calculator had been running just fine with it
this way since inception (it had nothing to do with the problem I was looking for).
I made note of it in a repair log for the unit, but left it as is. Someday it
night be interesting to take it out to measure it's characteristics.
1:53 p.m.
----------------------------------------
Date: Mon, 20 Apr 2009 21:40:51 -0700
From: hilpert at cs.ubc.ca
To: General at invalid.domain
Subject: Re: Reforming caps and CRTs
While we're giving electrolytic caps another go-round, here's another angle on
(modern) electrolytic caps:
I was repairing an HP 9815 (desktop programmable calc) a month ago. While
tracing it out to make the schematic, I noticed that a 680 uF, 25V electrolytic
cap for the +15V supply filter had been installed backwards (reversed
polarity).
---snip---
The cap is most likely completely dry inside. It would
have cooked completely by now. It is possible to reform a
cap backwards but that requires a slow current for
a long time. Of course, the capacitance would be really
small because the case has a small surface area compared
to the positive terminal.
Dwight
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9:34 p.m.
On 21 Apr 2009 at 6:53, dwight elvey wrote:
The cap is most likely completely dry inside. It
would
have cooked completely by now. It is possible to reform a
cap backwards but that requires a slow current for
a long time. Of course, the capacitance would be really
small because the case has a small surface area compared
to the positive terminal.
Good thing that the designers at HP didn't work for Earl "Madman"
Muntz. That kind of behavior (unit working even though a component
had failed) would have been a hanging offense.
--Chuck
7:04 p.m.
While we're giving electrolytic caps another go-round, here's another angle on
(modern) electrolytic caps:
I was repairing an HP 9815 (desktop programmable calc) a month ago. While
tracing it out to make the schematic, I noticed that a 680 uF, 25V electrolytic
I am wondering why you traced out the schematic of a 9815, when you can
download both the official service manual (boardswapper guide) and
unofficial full schematics (covering both main versions of the CPU board)
Anyway... the 9815 is a somewhat odd machine. It's the only HP desktop
computer before about 1980 that used a standard CPU. Other machines
either used a bit-serial processor built from TTL or HP custom
chips/hybrid modules. But the 9815 uses a 6800. The memory map (and thus
the address decoding circuitry) is a bit strange, mainly because they
wanted to put the 6821 PIA at location 0 (so they could use zero-page
addressing to access it), they wanted RAM in the rest of page 0, etc.
The PSU is, of course, a switching regulator run from a mains-frequency
step-down transformer. Strangely there's no crowbar circuit. If that
chopper transistor shorts, the 5V line leaps to about 30V with fatal
effects on all the chips. I don't know why HP cut corners in this way.
Can you tell I've worked on these before...
cap for the +15V supply filter had been installed
backwards (reversed
polarity). This was not a replacement or earlier repair, it came out of the
factory this way in 1975 (even HP screws up on occasion).
I've seen this too. In fact I've seen it twice rcently. The most recent
case was in that Hp120 I've been working on. The decouping capacitor for
the +12V line on one of the boards (connected from +12V to ground) was
fitted backwards. And the PCB was laid out backwards. HP, you see, put a
square pad for the 'indicated' lead of a component -- pin 1 of a
connector or IC, the +ve end of an electrolytic capacitor, the cathode
(banded end) of a diode, the emitter of a transistor, etc. And in this
case, the square pad was ground.
Of course I replaced the capacitor (10uF). I didn't keep the old one, I
have no idea if it had reformed backwards (i.e. with the oxide film on
the wrong plate), but I susepct it wasn't going to meet it's spec.
Granted that it's on the output of the regulator
so it's not as critical as if
it were the main smoothing cap right after the rectifiers, but it was
nonetheless interesting that the calculator had been running just fine with it
this way since inception (it had nothing to do with the problem I was looking for).
What was the fault?
I made note of it in a repair log for the unit, but left it as is. Someday it
night be interesting to take it out to measure it's characteristics.
Alas I didn't keep the one I replaced in the HP120, so I can't check that.
-tony
8:28 p.m.
On Tue, 2009-04-21 at 20:04 +0100, Tony Duell wrote:
The PSU is, of course, a switching regulator run from
a mains-frequency
step-down transformer. Strangely there's no crowbar circuit. If that
chopper transistor shorts, the 5V line leaps to about 30V with fatal
effects on all the chips. I don't know why HP cut corners in this way.
Shades of the Sony sets of the late 70s to mid 80s with the GCS power
supplies (Gate Controlled Switch, or Ghastly Catastrophic Semiconductor,
depending on who you ask). Oh, except that clapped full-wave rectified
mains across all the following regulators when (not if) it failed dead
short. Which promptly failed dead short too, with hilarious
consequences.
These would come in with the customer saying "It went bang and then the
picture and sound went off. It's probably just a fuse, it won't be too
expensive will it?" - and all the semiconductors inside are now black
sand...
Gordon
22 Apr
22 Apr
8:07 p.m.
On Tue, 2009-04-21 at 20:04 +0100, Tony Duell wrote:
Ah yes.. I rememeber those . There were various 'Great Conversions of
Semiconductors' to replace them with a bipolar chopper transistor like a
BU208A.
The PSU is, of course, a switching regulator run
from a mains-frequency
step-down transformer. Strangely there's no crowbar circuit. If that
chopper transistor shorts, the 5V line leaps to about 30V with fatal
effects on all the chips. I don't know why HP cut corners in this way.
Shades of the Sony sets of the late 70s to mid 80s with the GCS power
supplies (Gate Controlled Switch, or Ghastly Catastrophic Semiconductor, depending on who you ask). Oh, except that clapped
full-wave rectified
mains across all the following regulators when (not if) it failed dead
short. Which promptly failed dead short too, with hilarious
consequences.
This reminds me of the Boschert 2-stage PSUs used in some classic
computer equipment (PERQ1s, for example). The basic topology is that you
rectify and smooth mains (giving about 350V DC) and then ring that down
to about 150V using a non-isolated switching regulator. The output of
that feeds a couple of transistors running as a free-running oscillator
driving the main chopper transformer. The output of that is rectified and
smoothed. Feedback is then applied from the main (often +5V) output to
the 150V regulator. Controlling the output of that indirectly controls
the output voltage of the whole PSU of course.
Now for the nasty failuyre mode. The first chopper transistor (in the
150V regulator) goes short-circuit. So the output of that stage leaps to
about 350V. The second oscillator keeps on running, so all the PSU
outputs jump to over twice what they should be. At this point you hope
the crowbar fires, if notm you have a _lot_ of ICs to replace. If the
crowbar does fire, it shorts one of the outputs of the PSU. This causes
the second oscillaotr circuit to work harder and draw more current. This
is detected by the current limit circuit, which removes the drive from
(you guessed it) the 150V regulator chopper. Unfortunately, that is
shorted, so removing the drive doesn't do a darn thing. The 2 transsitors
in the second oscillator then go short-circuit. Now, across the 350V
rectified mains supply you have some shorted transistors, some windings
(both the inductor of the 150V regulator and the chopper transformer
primary), anf the current sense resistor (say 0.15 Ohms). That resisotr
then unrs out, taking the sense transistor with it. And then the chopper
control IC (a 723 IIRC), a few other transsitors and some small passives
'join the choir invisible'. Oh, and a couple of PCB tracks melt.
Yes, I have seen the aftermath of this. I also had to repair it....
These would come in with the customer saying "It
went bang and then the
picture and sound went off. It's probably just a fuse, it won't be too
Oh, the fuse proaly has failed. But as we all know, 'a transistor
protected by a fast-acting fuse will protect the fuse by lowing first'.
And the same applied to GCS devices.
-tony
21 Apr
21 Apr
11:13 p.m.
Tony Duell wrote:
You are free to wonder.
I suspect it is as Dwight was suggesting, the cap probably isn't doing much of
anything and the lack of C just doesn't matter in the scenario.
I was repairing an HP 9815 (desktop programmable
calc) a month ago. While
tracing it out to make the schematic, I noticed that a 680 uF, 25V electrolytic
I am wondering why you traced out the schematic of a 9815, when you can download both the official service manual
(boardswapper guide) and
unofficial full schematics (covering both main versions of the CPU board)
from http://www.hpmuseum.net/
The service manual I found previously, and contains the schematic only for
the power supply (which I had already RE'd by the time I found the manual).
IIRC, during a web search I saw something about a schematic or full service
manual available on a CD.
Anyway, it (my RE'd schematic) is all done.
Reading the ROM contents might be a future project.
Anyway... the 9815 is a somewhat odd machine. It's
the only HP desktop
What was the fault?
Symptoms were that sometimes certain (groups of) keys would not work. As might
be expected the groups corresponded to row/columns in the matrix, but the ones
that were dropping out didn't make sense in terms of the scan sequence. It
turned out merely that the +5/GND to the logic boards was a little low. Some
cleaning of an inter-board power supply connector and it was fine. One of the
keyboard scanning ICs had simply been the first to suffer as the supply dropped.
I made note
of it in a repair log for the unit, but left it as is. Someday it
night be interesting to take it out to measure it's characteristics.
Alas I didn't keep the one I replaced in the HP120, so I can't check that.
22 Apr
22 Apr
8:12 p.m.
Tony Duell wrote:
You are free to wonder.
I don;t know where you found that manual, but it is certainly available
I was repairing an HP 9815 (desktop programmable
calc) a month ago. While
tracing it out to make the schematic, I noticed that a 680 uF, 25V electrolytic
I am wondering why you traced out the schematic of a 9815, when you can download both the official service manual
(boardswapper guide) and
unofficial full schematics (covering both main versions of the CPU board)
from http://www.hpmuseum.net/
The service manual I found previously, and contains the schematic only for
the power supply (which I had already RE'd by the time I found the manual). from hpmusuem.net, along with the schematics of the
9815 (and many other
machines).
IIRC, during a web search I saw something about a
schematic or full service
manual available on a CD.
Ah yes,, the HPCC schematics CD. That contains the same schematics as on
hpmuseum.net along with a few others and ones for most of the LED HP
handhelds. FWIW, foe all I spent _many_ hours producing those, I don't
get a penny (cent, whatever) from the sale of the CD-ROM.
Anyway, it (my RE'd schematic) is all done.
Well, if people would rather produce their own, I'll stop doing them
unless I also need them....
Alas I
didn't keep the one I replaced in the HP120, so I can't check that.
I suspect it is as Dwight was suggesting, the cap probably isn't doing much of
anything and the lack of C just doesn't matter in the scenario.
21 Apr
21 Apr
8:37 a.m.
On Mon, 20 Apr 2009, Eric J Korpela wrote:
Some of the smoke came out of my Osborne 1 this
weekend. It doesn't
appear to have been fatal, as it was still functioning when I cut the
power. I'm giving the CRT some time to fully discharge before I open
it up, probably next weekend. It was probably a failing capacitor,
although it didn't explode, it merely got really warm over a period of
hours. But since there are some similar machines that I haven't
recently used, this question came to mind.
Oh my, this has nothing to do with either the CRT or any electrolytic
cap... I've had the same effect on an Osborne 1, and it was simply the
filter capacitor in the power supply that let its magic white smoke out.
The machine was still running though. Just replace that cap and finito...
Christian
1 p.m.
--- On Mon, 4/20/09, Eric J Korpela <korpela at ssl.berkeley.edu> wrote:
Some of the smoke came out of my Osborne 1 this
weekend. It
doesn't
appear to have been fatal, as it was still functioning when
I cut the
power. I'm giving the CRT some time to fully discharge
before I open
it up, probably next weekend. It was probably a failing
capacitor,
although it didn't explode, it merely got really warm
over a period of
hours. But since there are some similar machines that I
haven't
recently used, this question came to mind.
Does the Osborne have a tantalum capacitor in it? Those tend to blow without warning, for
no good reason. When they go, you get lots of magic smoke and burning - but your device
tends to stay working. Filter caps can go with smoke too - and depending on the deivce, it
might keep going, or fail.
I think people get really way over-concerned about electrolytics. These devices are old...
but not that old. Slow powerup would be a good idea for seriously old stuff (pre-50's,
mainly), primarily just to check for shorts. I use a series light bulb for that. But if
the cap is bad enough that it's going to exlplode on powerup, it isn't going to
reform to a useable state.
This is one of those often discussed "holy war" topics, and comes up once a year
or so. My mindset has always been to cross my fingers and plug it in, especially for
common, documented things like an Osborne or a TRS-80. If a capacitor blows up, then you
know that it's bad, and should be replaced - and it's marked clearly with a
smoking hole. For rarer things, I try to go in stages, testing the power supply first with
a dummy load to ensure that it's good before going on.
But the fact of the matter is, when you're working with old stuff, you are going to be
replacing a fair number of electrolytic capacitors. They just don't last. And the
typical failure mode has them simply operating poorly - not exploding.
A tradition at VCF East is the releasing of the magic smoke (Andy is usually on top of
this one), and while spactacular, all affected devices have since been repaired. (Canon
Cat, Apple IIe, Kaypro, Apple ProFile...)
-Ian
7:26 p.m.
Does the Osborne have a tantalum capacitor in it? Those tend to blow
without warning, for no good reason. When they go, you get lots of magic
And no amount of testing/reforming will solve that. They test find and
one day they emit clouds of foul-smelling smoke and glow red. Just
replace them when it happens/
smoke and burning - but your device tends to stay
working. Filter caps
can go with smoke too - and depending on the deivce, it might keep going,
or fail.
I've had the metalised paper capacitors in mains filters fail without
warning. When one goes, I normally replaec all of them, but other than
that I can see no way of telling when they're about to fail
I think people get really way over-concerned about electrolytics.
I owuld agree. I've had capacitors fail, of course. But it's not a common
failure in any of the machines I work on (which are, I admit, made after
1970, but covers just about everything after that date).
These devices are old... but not that old. Slow
powerup would be a good
idea for seriously old stuff (pre-50's, mainly), primarily just to check
for shorts. I use a series light bulb for that. But if the cap is bad
I suesw a series light bulb when repairing SMPSUs too, just to limit the
current if something goes seriously wrong. And I used one on a
transformer/rectifier/smoothing capactor PSU in my HP9826. It arrived
with the mains fuse blown, I could find nothing wrong (the regulator
board worked fine off a bench supply -- in fact I could run the entire
machine that way, the smoothing capacitor was fine, the rectifier diodes
were fine, the trnasformer 'Meggered' OK, and so on).
I don't find a Variac to be a particularly useful piece of kit for
working on classic computers
enough that it's going to exlplode on powerup, it
isn't going to reform
to a useable state.
This is one of those often discussed "holy war" topics, and comes up
once a year or so. My mindset has always been to cross my fingers and
plug it in, especially for common, documented things like an Osborne or
a TRS-80. If a capacitor blows up, then you know that it's bad, and
should be replaced - and it's marked clearly with a smoking hole. For
rarer things, I try to go in stages, testing the power supply first with
a dummy load to ensure that it's good before going on.
I always run the PSU on a dummy load if I possibly can. Just in case
something has come lose in shipping, etc.
And I run the supply on a dummy load after working on the machine
(particularly if I've been working on the PSU area). We all make
mistakes, and the time it takes to do this is a lot less than the time it
takes to replace 100 ICs or more!
I will also add that I do a visual inspection, including electrolytic
capacitors. For example, when looking over this HP120 I've been working
on, I noticed one of the mains smoothing capacitors on the SMPSU board
was bulging on top. It worked fine, it seemed to test fine, but I
replaced the pair for my peace of mind. Thing is, they are mounted next
to the CRT neck, and while they have that weakened area on top to let
them vent without exploding, I'd rather they didn't do that next to a
CRT. So I changed them.
-tony
6:21 p.m.
Some of the smoke came out of my Osborne 1 this weekend. It doesn't
appear to have been fatal, as it was still functioning when I cut the
power. I'm giving the CRT some time to fully discharge before I open
it up, probably next weekend. It was probably a failing capacitor,
I don't know why people are so worried about the residual charge on a
CRT. Unless you're working on the CRT or flyback transformer, there's no
way you're going to come into contact with it.
And I am not sure what good waiting a week does. If there's a bleeder
resistor, it'll discharge in minutes. Similarly on a _working_ device,
the beam current will often discharge the CRT at power-down (I find it
rare to find much residual voltage on a CRT final anode connector). If
neitehr of these is the case, then a week may well not be long enough.
although it didn't explode, it merely got really
warm over a period of
hours. But since there are some similar machines that I haven't
recently used, this question came to mind.
I've used the variac technique to reform capacitors, but thus far
haven't done this on a machine that contains a CRT because I don't
know what the reduced voltage is going to do to the CRT. The next
The CRT is the least of your worries.
I am not sure what good applying a Variac to the mains input of a machine
using regulated supplies actually does. It's noy going to do much
reforming of capacitors deep in the circuitry. And if the PSU is a
switcher (and a lot are), it can do damage (switchers are constant
_power_ loads to a very good approximation, they draw more current at
lower voltage).
if you want to reform the capacitors, IMHO you need to remove them and
run them up on a current-limited DC supply.
Even then I am not sure what the point is. I've found capacitors,
particularly tantalum bead types, just fail at random. I don;t think
reforming them would help.
-tony
5730
days inactive
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19 comments
10 participants
participants (10)
-
aek＠bitsavers.org -
ard＠p850ug1.demon.co.uk -
cc＠informatik.uni-stuttgart.de -
cclist＠sydex.com -
dkelvey＠hotmail.com -
gordonjcp＠gjcp.net -
hilpert＠cs.ubc.ca -
ian_primus＠yahoo.com -
js＠cimmeri.com -
korpela＠ssl.berkeley.edu