30 Nov
2007
30 Nov
'07
10:40 a.m.
On Thu, 29 Nov 2007 12:02:05 -0700, J Blaser
<oldcpu2 at rogerwilco.org>wrote:
In fact, a
couple of the PS PCBs went through the dishwasher to clean up the
remains to 'rodent residue'. On the whole, it seems that I got them
back together properly! ;)
If there are any potentiometers on the boards that you washed, you
might want to ensure that the wipers are making contact. Generally,
pots are installed after a board wash unless they are sealed. An open
wiper will cause many of the symptoms you are describing.
An easy method is to measure the resistance across the pot and then
the resistance from each leg to the wiper. The sum of the wiper to
legs should equal the resistance across the pot.
If the wiper appears to be disconnected, mark its position and then
rotate the wiper through its travel and then back to the mark. If
this fails to restore contact or the wiper contact is intermittent,
replace the pot - it's not worth the effort trying to save a failing
potentiometer.
CRC
30 Nov
30 Nov
10:01 p.m.
Quoting CRC <technobug at comcast.net>:
On Thu, 29 Nov 2007 12:02:05 -0700, J Blaser
<oldcpu2 at rogerwilco.org>wrote:
Luckily, no potentiometers on the boards I washed. I was concerned about this
issue, too, but when I looked over the two boards that I planned to wash, I was
glad to find that neither had any 'moving parts' components, mostly just
descrete stuff, with an odd IC or two. I think I'm okay on this issue.
- Jared
In fact, a
couple of the PS PCBs went through the dishwasher to clean up the
remains to 'rodent residue'. On the whole, it seems that I got them
back together properly! ;)
If there are any potentiometers on the boards that you washed, you
might want to ensure that the wipers are making contact. Generally,
pots are installed after a board wash unless they are sealed. An open
10:30 p.m.
Here's the latest update on the power supply adventures...
Tonight I put a load, as suggested, on the 2.5V power supply (and the 5V PS) by
attaching a pair of automobile headlamps to each supply. I wired both lamps
(for each PS) in parallel with each other, and with the two filaments (Hi- and
Lo-Beam) in parallel, too. That gave me four filaments for each power supply as
a load.
As a result, when I power up, happily the "2.5V FAIL" and the every-8-seconds
"OVER VOLTAGE" indications are no longer seen. The voltage on the 2.5V PS
output is a rock steady 2.5V.
However, on the 5V PS, I'm seeing only +0.85V on the outputs, and I am still
seeing the "REG FAIL" indication on the power controller. Obviously there's
still a problem in the 5V PS. Using the "VAX-11/750 H7104 Power System
Technical Description" doc's fault isolation procedure, which suggests that the
+/-15V regulator is broken in the 5V PS, I checked the +/-15V outputs. I should
see +15V and -15V, but I'm seeing +7.9 (or so, it's not quite stable) on both
outputs even the one that should be negative. The fault isolation procedure in
that doc doesn't go any further at this point than to suggest a replacement of
the entire 5V power supply box.
I'd love to repair it, but I'm certainly not as smart as Tony, nor am I likely
to ever figure out the faulty component(s) directly. There is a main
'motherboard', two plug in PCBs, and other bolt-on components galore, and while
I can follow some logic circuit diagrams, I'm clearly out of my league with
analog/PS stuff. Besides, I haven't been able locate schematics for this power
system. Soooo....
Anyone have a spare H7104D 5V PS for this baby??? ;P Aside from the tongue-in-
cheekiness, does anyone have schematics and/or Engineering Drawings for this 11/
750. Maybe I could actually try to sort it out if I had some more information,
at least until I electrocute myself! :o
Thanks!
- Jared
1 Dec
1 Dec
12:18 a.m.
Quoting J Blaser <oldcpu2 at rogerwilco.org>:
Anyone have a spare H7104D 5V PS for this baby??? ;P
Aside from the
tongue-in-cheekiness, does anyone have schematics and/or
Engineering Drawings for this 11/750. Maybe I could actually try
to sort it out if I had some more information, at least until I electrocute
myself! :o
Well, I should have looked harder... I found the Print Sets for both the 2.5V
and 5V power supplies on vt100.net/manx. Hopefully, a little study will
give me a hint.
- Jared
4 Dec
4 Dec
12:30 a.m.
New subject: Torode Disk drive Controller
Hi
I've finally found something that I've been looking for for over
10 years.
I have one of the Digital Systems drive and controller boxes.
About 8 years ago, I decompiled the state machine in this
controller to figure out how it worked.
Even though getting it working in the system, I've been off and
on looking for the manual. I finally located someone that
actually has a manual ;)
It is funny how when one thinks it is a hopeless cause,
something pops up.
This controller is interesting because it was used on the
first S-100 machine that had an official CP/M installed on
it ( not my controller but the same model ).
It seems that John Torode and Kildall worked on the controller
together and he ported his CP/M to the S-100 world.
Dwight
_________________________________________________________________
Put your friends on the big screen with Windows Vista? + Windows Live?.
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1 Dec
1 Dec
4:31 a.m.
J Blaser wrote:
I'd love to repair it, but I'm certainly not
as smart as Tony, nor am
I likely
to ever figure out the faulty component(s) directly. There is a main
'motherboard', two plug in PCBs, and other bolt-on components galore,
and while
I can follow some logic circuit diagrams, I'm clearly out of my
league with analog/PS stuff.
You seem to have managed to wiled a voltmeter and not hurt yourself
inside the PSU. Sureley the worst that can happen is that you'll
end up at the point where you need to fix component X and you
are unable/unwilling to do so?
People have been talked through some tricky procedures on this
list ... For that matter this is maybe the 3rd VAX-11/750 with
the "REG FAIL" fault and I don't recall ever hearing of one
getting fixed. Someone has to be the first :-)
Besides, I haven't been able locate schematics
for this power
system. Soooo....
There should be a full set of schematics on Manx: http://vt100.net/manx.
I scanned a full set for the first person I came across with this
problem, so while I'm not 100% sure the PSU schematics are in there,
I am 99% sure ...
Antonio
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29/11/2007 20:32
5:17 p.m.
People have been talked through some tricky procedures
on this
list ... For that matter this is maybe the 3rd VAX-11/750 with
the "REG FAIL" fault and I don't recall ever hearing of one
getting fixed. Someone has to be the first :-)
Unforutnately (?) I've always kept well clear of the 11/750. I really
wouldn't want to maitain that CPU....
But I can be eaily persuaded to look at the PSU schematics sometime and
see if I spot anything obvious. Or at least tlak you through the design
(which might be somewhat unconventional if other DEC supplies are
anything to go by [1])
[1] This might not be a problem for you. If oyu don't have any experience
of SMPSUs, any one is as good/bad as another to get started with. The
problems generally come if you have fixed ideas ofg how supplies should
work and then you get something strange thrown at you.
-tony
6:03 p.m.
From: ard at p850ug1.demon.co.uk
Hi
One of the trickiest things about switchers is that they often
use the main output to provide the rails for the regulation feedback.
This causes a chicken/egg problem. We can see that there is
no output so no feedback to tell the high side to deliver more
voltage ( had just such a problem on my Olivetti M20 supply ).
These circuits often have some way to kick start the supply
by pulsing the high side once on powerup, delivering just enough
current to the regulator feed back to get the hole thing started.
This type of circuit is unlikely on a 11/750 ( without actually
looking at the supply schematic ). They most likely have a separate
transformer and analog supply to power the regulator feedback.
I was just showing that these can be tricky compared to
analog supplies. The problem was located in the feedback.
Dwight
_________________________________________________________________
Share life as it happens with the new Windows Live.Download today it's FREE!
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People have been talked through some tricky
procedures on this
list ... For that matter this is maybe the 3rd VAX-11/750 with
the "REG FAIL" fault and I don't recall ever hearing of one
getting fixed. Someone has to be the first :-)
Unforutnately (?) I've always kept well clear of the 11/750. I really
wouldn't want to maitain that CPU....
But I can be eaily persuaded to look at the PSU schematics sometime and
see if I spot anything obvious. Or at least tlak you through the design
(which might be somewhat unconventional if other DEC supplies are
anything to go by [1])
[1] This might not be a problem for you. If oyu don't have any experience
of SMPSUs, any one is as good/bad as another to get started with. The
problems generally come if you have fixed ideas ofg how supplies should
work and then you get something strange thrown at you.
2 Dec
2 Dec
5:25 p.m.
One of the trickiest things about switchers is that
they often
use the main output to provide the rails for the regulation feedback.
This causes a chicken/egg problem. We can see that there is
no output so no feedback to tell the high side to deliver more
If there is no feedback -- that is the feedback detects no output
voltage, then the power supply controller should try to increase the
output voltage. That's why a fault in the feedback circuit -- even
unconencted sense terminals in some poorly-designed supplies -- will get
the outputs to go sky-high. Hopefully the overvoltage protection circuit
(crowbar or whatever) trips before any real damage is done.
You might be confusing this issue with another one. That is, the power
supply control circuitry needs to be powered. Once the supply is
running, it; can be powered from one of the outputs of said supply, but
at swich-on, the power supply outputs are all 0, to the power control
circuitry is not powered, so the supply can't do anything, so the outputs
remain at 0.
Some larger supplies -- even things like the VT100 -- have a little linear
supply to get things going. Other times there's a dropping resistor
(startup resistor) to power some bits of the control circuit directly
from the recifiied mians, just to get it all going.
Once it's started up,
it carries on running from the main supply outputs.
DEC took this to extremes in the 11/44. The main PSU circuits (and there
are 2 of them) in that machine start from a little SMPSU circuit. That in
turn has a startup resistor.
-tony
8:51 p.m.
Quoting Tony Duell <ard at p850ug1.demon.co.uk>:
But I can be eaily persuaded to look at the PSU
schematics sometime and
see if I spot anything obvious. Or at least tlak you through the design
(which might be somewhat unconventional if other DEC supplies are
anything to go by [1])
[1] This might not be a problem for you. If oyu don't have any experience
of SMPSUs, any one is as good/bad as another to get started with. The
problems generally come if you have fixed ideas ofg how supplies should
work and then you get something strange thrown at you.
Thanks much for the offer to work me through this! There are a couple of things
that I want to do tomorrow night when I get a chance.
Clint's suggested that there is something 'shorting' the supplies outputs has
prompted me to consider disconnecting all outputs (+5V, +/-15V) from the
backplane, and *only* hook up my auto headlamps as a load. I don't know that
this will give me anything useful, but I'll give it a try.
Based on those results, I might be ready to cry, "Uncle!" and ping you for some
advice. I do like Clint's suggestion to solder some wires to various points,
bringing them to the outside for measurement (that's just the sort of thing I
would not have thought of...thanks, Clint!), so that might be a good next step.
More soon (after my only-headlamps-connected test)...
- Jared
4 Dec
4 Dec
5:48 p.m.
New subject: VAX 11/750 5V PS troubleshooting
J Blaser wrote:
Quoting Tony Duell <ard at
p850ug1.demon.co.uk>:
I finally got a little time to take another look at this 5V supply.
I removed all connections to the backplane, etc., then connected my
4-filament rig of headlamps as the only load and powered up. I see the
same results as before, about 0.8V (a bit variable) on the 5V output.
So I guess we can safely say that the problem lies within the PS itself,
and not in anything that it's connected to. I'll add that I hear a
not-loud-but-noticable 'DZZZ' sound from the PS (not just now, it's been
there from the beginning), probably the crowbar doing something. Still,
I think I have a suitable load with the headlamps.
Tony, if your offer still stands, I'd appreciate some advice on how best
to proceed. If you could give me a couple of ideas about what would be
good test points to get started with, I'll give it a go. As I said
earlier, I have a modest set of tools, e.g., VOM and oscilloscope.
I have the 2.5V (H7104-C) and 5V (H7104-D) PSU printsets, found at:
http://vt100.net/mirror/hcps/h7104-c.pdf
http://vt100.net/mirror/hcps/h7104-d.pdf
I admit, I'm not making much sense of them at the moment.
FWIW, I have no experience working inside of switching PSUs, so I have
no knowledge (good or bad) to draw upon.
Many thanks.
- Jared
But I can be eaily persuaded to look at the PSU
schematics sometime and
see if I spot anything obvious. Or at least tlak you through the design
(which might be somewhat unconventional if other DEC supplies are
anything to go by [1])
[1] This might not be a problem for you. If oyu don't have any experience
of SMPSUs, any one is as good/bad as another to get started with. The
problems generally come if you have fixed ideas ofg how supplies should
work and then you get something strange thrown at you.
Thanks much for the offer to work me through this! There are a couple of things
that I want to do tomorrow night when I get a chance. 
1 Dec
1 Dec
12:56 p.m.
On Nov 30, 2007, at 10:30 PM, J Blaser wrote:
Anyone have a spare H7104D 5V PS for this baby??? ;P
Aside from the
tongue-in-
cheekiness, does anyone have schematics and/or Engineering Drawings
for this 11/
750. Maybe I could actually try to sort it out if I had some more
information,
at least until I electrocute myself! :o
I'm fairly certain that I have 11/750 prints here, but I will have to
find them. Let me know if you don't find them elsewhere quickly enough
and I'll start digging.
-Dave
--
Dave McGuire
Port Charlotte, FL
4:41 p.m.
Quoting Dave McGuire <mcguire at neurotica.com>:
On Nov 30, 2007, at 10:30 PM, J Blaser wrote:
Thanks, Dave, for the offer (and to all others giving helpful advice in this
thread). I *did* find the schematics last night on vt100.net/manx, so I just
need to spend some time now looking them over, and seeing what I can do.
I do have some very basic tools, and a 'scope, and I guess my plan is to try to
look for some bad passives first, unpowered, then take whatever next steps seem
reasonable. These PSs are pretty tightly packed, in a 3-D kind of way, and I'm
not sure I'm up to poking around inside with it powered. I might touch
something I shouldn't with a probe, and make things worse! ;) We will see...
As things progress I'll give a report, but don't hold your breath for quick
news. I've got a lot to learn first.
Thanks.
- Jared
cheekiness, does anyone have schematics and/or
Engineering Drawings
for this 11/
750. Maybe I could actually try to sort it out if I had some more
information,
at least until I electrocute myself! :o
I'm fairly certain that I have 11/750 prints here, but I will have to
find them. Let me know if you don't find them elsewhere quickly enough
and I'll start digging. 
10:03 p.m.
On Sat, 1 Dec 2007, J Blaser wrote:
Quoting Dave McGuire <mcguire at
neurotica.com>:
I like to solder wires to interesting points, run them outside of
whatever I'm working and attach them to a something (paint stir stick)
so they don't short out. That way I can look at the signals without
risking a short, especially on high voltage stuff.
Clint
On Nov 30, 2007, at 10:30 PM, J Blaser wrote:
Thanks, Dave, for the offer (and to all others giving helpful advice in this
thread). I *did* find the schematics last night on vt100.net/manx, so I just
need to spend some time now looking them over, and seeing what I can do.
I do have some very basic tools, and a 'scope, and I guess my plan is to try to
look for some bad passives first, unpowered, then take whatever next steps seem
reasonable. These PSs are pretty tightly packed, in a 3-D kind of way, and I'm
not sure I'm up to poking around inside with it powered. I might touch
something I shouldn't with a probe, and make things worse! ;) We will see...
As things progress I'll give a report, but don't hold your breath for quick
news. I've got a lot to learn first.
Thanks.
- Jared
cheekiness, does anyone have schematics and/or
Engineering Drawings
for this 11/
750. Maybe I could actually try to sort it out if I had some more
information,
at least until I electrocute myself! :o
I'm fairly certain that I have 11/750 prints here, but I will have to
find them. Let me know if you don't find them elsewhere quickly enough
and I'll start digging.
6108
days inactive
6112
days old
13 comments
7 participants
participants (7)
-
arcarlini＠iee.org -
ard＠p850ug1.demon.co.uk -
cctech＠vax-11.org -
dkelvey＠hotmail.com -
mcguire＠neurotica.com -
oldcpu2＠rogerwilco.org -
technobug＠comcast.net