9 Oct
2015
9 Oct
'15
8:42 p.m.
Hey all --
Once again, I find myself in over my head debugging a power supply, this
time an H7140 from a PDP-11/44. Here's the skinny:
I examined the supply physically before experimenting and found a
capacitor on the Bias/Interface board that was leaking, bursting and
rather burned-out looking (not a great sign) -- this is capacitor C4 in
the printsets on Bitsavers
(http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/1144/MP00897_11X…)
Everything else looked OK physically; I replaced the obviously bad
capacitor at C4.
When power is applied (plugged in, breaker switch flipped to "On") the
relay does not click - based on my readings of the manuals this should
happen after the bias voltages are up to spec. I measure 308VDC on the
lugs on the top of the memory board, so that's at least something
working. Getting to other points to test voltages is a bit more
difficult, especially with those high voltages in the way, what a nice
design :).
Switching the front panel switch to "Local" (or any other position) has
no effect -- no fans, no LEDs, nothing. I've double-checked all the
wiring and everything looks OK.
Capacitor C4 looks to be involved with the START-UP DRIVE signal
circuitry (which drives the relay) so the behavior I'm seeing makes
sense if C4 died and took a couple of things with it (or if something
else died and took C4 with it).
Here's where it gets kind of odd -- I spent some time testing diodes and
transistors in the related area near C4 and while doing so I noticed
that there are four diodes (D1-D4) listed on the schematic that are
missing from my board. "Missing" as in someone clipped them out at some
point -- there are just nubs of the leads left. I'm not sure why this
would have been done, but there were a number of ECOs applied to this
board (a few wires and resistors added) and I don't want to assume that
if I just put four new diodes in that it won't cause other problems.
Anyone know if there were other revision levels of the bias/interface
board that would have done away with these diodes? Anyone have an H7140
they can easily crack open to compare? (It's actually relatively easy
to get to, if you can get to the supply...)
Thanks as always,
Josh
9 Oct
9 Oct
9:13 p.m.
On 10/9/2015 10:42 PM, Josh Dersch wrote:
Capacitor C4 looks to be involved with the START-UP DRIVE signal
circuitry (which drives the relay) so the behavior I'm seeing makes
sense if C4 died and took a couple of things with it (or if something
else died and took C4 with it).
Here's where it gets kind of odd -- I spent some time testing diodes and
transistors in the related area near C4 and while doing so I noticed
that there are four diodes (D1-D4) listed on the schematic that are
missing from my board. "Missing" as in someone clipped them out at some
point -- there are just nubs of the leads left. I'm not sure why this
would have been done, but there were a number of ECOs applied to this
board (a few wires and resistors added) and I don't want to assume that
if I just put four new diodes in that it won't cause other problems.
Anyone know if there were other revision levels of the bias/interface
board that would have done away with these diodes? Anyone have an H7140
they can easily crack open to compare? (It's actually relatively easy
to get to, if you can get to the supply...)
Thanks as always,
Josh
I have an HP drive (RK05 type packs) whose startup power supply had been
tampered with in very odd ways - missing parts, etc. (and maybe even
blown out circuit board traces - I forget - I haven't worked on that
drive in years). I seem to recall that it looked like it had failed
catastrophically at some point. I ended up wiring in a 24V stand
alone supply temporarily as a startup supply and got the rest of the
supply going that way. Maybe someone did something similar with your
supply, and then ran out of time / gave up. Perhaps they clipped the
diodes out to test them.
I have an 11/40 and an 11/45, so I probably have an H7140 (but I don't
seem to have a spare anywhere, which surprises me a little, because I
got parts of another 11/40 at one point), but I recall that the things
are nightmare-ishly heavy to mount, and there is only one of me, so
unless the area in question is visible without taking the supply out of
the rack, I doubt that I can help very quickly.
JRJ
9:22 p.m.
On 10/9/15 9:13 PM, Jay Jaeger wrote:
On 10/9/2015 10:42 PM, Josh Dersch wrote:
Oh crap -- I just noticed that the subject line says 11/40; it's
supposed to be *11/44*. Fingers faster than brain (as is usually the case.)
As you may imagine, the 11/44 has a completely different supply than the
11/40...
- Josh
Capacitor C4 looks to be involved with the
START-UP DRIVE signal
circuitry (which drives the relay) so the behavior I'm seeing makes
sense if C4 died and took a couple of things with it (or if something
else died and took C4 with it).
Here's where it gets kind of odd -- I spent some time testing diodes and
transistors in the related area near C4 and while doing so I noticed
that there are four diodes (D1-D4) listed on the schematic that are
missing from my board. "Missing" as in someone clipped them out at some
point -- there are just nubs of the leads left. I'm not sure why this
would have been done, but there were a number of ECOs applied to this
board (a few wires and resistors added) and I don't want to assume that
if I just put four new diodes in that it won't cause other problems.
Anyone know if there were other revision levels of the bias/interface
board that would have done away with these diodes? Anyone have an H7140
they can easily crack open to compare? (It's actually relatively easy
to get to, if you can get to the supply...)
Thanks as always,
Josh
I have an HP drive (RK05 type packs) whose startup power supply had been
tampered with in very odd ways - missing parts, etc. (and maybe even
blown out circuit board traces - I forget - I haven't worked on that
drive in years). I seem to recall that it looked like it had failed
catastrophically at some point. I ended up wiring in a 24V stand
alone supply temporarily as a startup supply and got the rest of the
supply going that way. Maybe someone did something similar with your
supply, and then ran out of time / gave up. Perhaps they clipped the
diodes out to test them.
I have an 11/40 and an 11/45, so I probably have an H7140 (but I don't
seem to have a spare anywhere, which surprises me a little, because I
got parts of another 11/40 at one point), but I recall that the things
are nightmare-ishly heavy to mount, and there is only one of me, so
unless the area in question is visible without taking the supply out of
the rack, I doubt that I can help very quickly.
JRJ
9:22 p.m.
New subject: DEC H7140 (11/44) power supply revisions and general advice?
And as I just noted after Jay's response, the subject line should say
"11/44" not "11/40." Corrected...
- Josh
On 10/9/15 8:42 PM, Josh Dersch wrote:
Hey all --
Once again, I find myself in over my head debugging a power supply,
this time an H7140 from a PDP-11/44. Here's the skinny:
I examined the supply physically before experimenting and found a
capacitor on the Bias/Interface board that was leaking, bursting and
rather burned-out looking (not a great sign) -- this is capacitor C4
in the printsets on Bitsavers
(http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/1144/MP00897_11X…)
Everything else looked OK physically; I replaced the obviously bad
capacitor at C4.
When power is applied (plugged in, breaker switch flipped to "On") the
relay does not click - based on my readings of the manuals this should
happen after the bias voltages are up to spec. I measure 308VDC on
the lugs on the top of the memory board, so that's at least something
working. Getting to other points to test voltages is a bit more
difficult, especially with those high voltages in the way, what a nice
design :).
Switching the front panel switch to "Local" (or any other position)
has no effect -- no fans, no LEDs, nothing. I've double-checked all
the wiring and everything looks OK.
Capacitor C4 looks to be involved with the START-UP DRIVE signal
circuitry (which drives the relay) so the behavior I'm seeing makes
sense if C4 died and took a couple of things with it (or if something
else died and took C4 with it).
Here's where it gets kind of odd -- I spent some time testing diodes
and transistors in the related area near C4 and while doing so I
noticed that there are four diodes (D1-D4) listed on the schematic
that are missing from my board. "Missing" as in someone clipped them
out at some point -- there are just nubs of the leads left. I'm not
sure why this would have been done, but there were a number of ECOs
applied to this board (a few wires and resistors added) and I don't
want to assume that if I just put four new diodes in that it won't
cause other problems. Anyone know if there were other revision levels
of the bias/interface board that would have done away with these
diodes? Anyone have an H7140 they can easily crack open to compare?
(It's actually relatively easy to get to, if you can get to the
supply...)
Thanks as always,
Josh
10 Oct
10 Oct
4:15 a.m.
2015-10-10 5:42 GMT+02:00 Josh Dersch <derschjo at gmail.com>:
Hey all --
First of all I haven't poked around in the PSU of my 11/44 since it worked
fine when powered up. But the design of the H7140 is a lot similar to the
design of the H7104, the PSU of the VAX-11/750 which I worked quite a lot
with.
http://www.datormuseum.se/computers/digital-equipment-corporation/vax-11-750
Once again, I find myself in over my head debugging a
power supply, this
time an H7140 from a PDP-11/44. Here's the skinny:
I examined the supply physically before experimenting and found a
capacitor on the Bias/Interface board that was leaking, bursting and rather
burned-out looking (not a great sign) -- this is capacitor C4 in the
printsets on Bitsavers (
http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/1144/MP00897_11X…)
Everything else looked OK physically; I replaced the obviously bad
capacitor at C4.
When power is applied (plugged in, breaker switch flipped to "On") the
relay does not click - based on my readings of the manuals this should
happen after the bias voltages are up to spec. I measure 308VDC on the
lugs on the top of the memory board, so that's at least something working.
Getting to other points to test voltages is a bit more difficult,
especially with those high voltages in the way, what a nice design :).
The previous owner said that it happens that the relays get stuck. The
relay is there to limit the inrush current so when it clicks it bypasses a
couple of power resistors. Regardless relay state you will have the full
voltage over the capacitors. (at least this is the case in the H7104). If
the relay get stuck then the power resistors get very hot. The relay drive
circuit detects that the voltage is high enough then turns on the relay.
Maybe something in this circuitry is bad. In this case you could force it
to on but then I think you should power it from a variac
Switching the front panel switch to "Local"
(or any other position) has no
effect -- no fans, no LEDs, nothing. I've double-checked all the wiring
and everything looks OK.
Have you verified that you have the 12V BIAS voltage? If not you could
probably generate the 12V BIAS voltage using a lab power supply just to see
if the main switcher is working properly.
I used an insulation transformer and a variac and then forced the relay
drive to on. In the H7104 the same circuitry also enabled the main switcher
so unless I did this there were no fun at all. I supplied 12V using a bench
supply. It made it possible to check everything was working ok without any
high voltages.
Capacitor C4 looks to be involved with the START-UP DRIVE signal circuitry
(which drives the relay) so the behavior I'm seeing makes sense if C4 died
and took a couple of things with it (or if something else died and took C4
with it).
Here's where it gets kind of odd -- I spent some time testing diodes and
transistors in the related area near C4 and while doing so I noticed that
there are four diodes (D1-D4) listed on the schematic that are missing from
my board. "Missing" as in someone clipped them out at some point -- there
are just nubs of the leads left. I'm not sure why this would have been
done, but there were a number of ECOs applied to this board (a few wires
and resistors added) and I don't want to assume that if I just put four new
diodes in that it won't cause other problems. Anyone know if there were
other revision levels of the bias/interface board that would have done away
with these diodes? Anyone have an H7140 they can easily crack open to
compare? (It's actually relatively easy to get to, if you can get to the
supply...)
Thanks as always,
Josh
8:45 a.m.
On Oct 10, 2015, at 4:15 AM, Mattis Lind
<mattislind at gmail.com> wrote:
2015-10-10 5:42 GMT+02:00 Josh Dersch <derschjo at gmail.com <mailto:derschjo at
gmail.com>>:
Thanks. I should have mentioned, but I tested out the relay and it?s not stuck and seems
to be working fine. It definitely looks like the relay control circuitry is not running
properly.
Hey all --
First of all I haven't poked around in the PSU of my 11/44 since it worked
fine when powered up. But the design of the H7140 is a lot similar to the
design of the H7104, the PSU of the VAX-11/750 which I worked quite a lot
with.
http://www.datormuseum.se/computers/digital-equipment-corporation/vax-11-750
<http://www.datormuseum.se/computers/digital-equipment-corporation/vax-11-750>
Once again, I find myself in over my head
debugging a power supply, this
time an H7140 from a PDP-11/44. Here's the skinny:
I examined the supply physically before experimenting and found a
capacitor on the Bias/Interface board that was leaking, bursting and rather
burned-out looking (not a great sign) -- this is capacitor C4 in the
printsets on Bitsavers (
http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/1144/MP00897_11X…)
Everything else looked OK physically; I replaced the obviously bad
capacitor at C4.
When power is applied (plugged in, breaker switch flipped to "On") the
relay does not click - based on my readings of the manuals this should
happen after the bias voltages are up to spec. I measure 308VDC on the
lugs on the top of the memory board, so that's at least something working.
Getting to other points to test voltages is a bit more difficult,
especially with those high voltages in the way, what a nice design :).
The previous owner said that it happens that the relays get stuck. The
relay is there to limit the inrush current so when it clicks it bypasses a
couple of power resistors. Regardless relay state you will have the full
voltage over the capacitors. (at least this is the case in the H7104). If
the relay get stuck then the power resistors get very hot. The relay drive
circuit detects that the voltage is high enough then turns on the relay.
Maybe something in this circuitry is bad. In this case you could force it
to on but then I think you should power it from a variac Switching the front panel switch to
"Local" (or any other position) has no
effect -- no fans, no LEDs, nothing. I've double-checked all the wiring
and everything looks OK.
Have you verified that you have the 12V BIAS voltage? If not you could
probably generate the 12V BIAS voltage using a lab power supply just to see
if the main switcher is working properly.
I used an insulation transformer and a variac and then forced the relay
drive to on. In the H7104 the same circuitry also enabled the main switcher
so unless I did this there were no fun at all. I supplied 12V using a bench
supply. It made it possible to check everything was working ok without any
high voltages.
>
> Capacitor C4 looks to be involved with the START-UP DRIVE signal circuitry
> (which drives the relay) so the behavior I'm seeing makes sense if C4 died
> and took a couple of things with it (or if something else died and took C4
> with it).
>
> Here's where it gets kind of odd -- I spent some time testing diodes and
> transistors in the related area near C4 and while doing so I noticed that
> there are four diodes (D1-D4) listed on the schematic that are missing from
> my board. "Missing" as in someone clipped them out at some point -- there
> are just nubs of the leads left. I'm not sure why this would have been
> done, but there were a number of ECOs applied to this board (a few wires
> and resistors added) and I don't want to assume that if I just put four new
> diodes in that it won't cause other problems. Anyone know if there were
> other revision levels of the bias/interface board that would have done away
> with these diodes? Anyone have an H7140 they can easily crack open to
> compare? (It's actually relatively easy to get to, if you can get to the
> supply...)
>
> Thanks as always,
> Josh
10:14 a.m.
If I remember correctly I had a problem in this area that turned out to be a loose/dry
joint where the two thermistors that are across the relay joined together. In my case it
was an intermittent fault though.
Regards
Rob
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Josh Dersch
Sent: 10 October 2015 16:46
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: DEC H7140 (11/40) power supply revisions and general advice?
something working.
turns on the relay.
Interesting idea, I?ll look into that. Thanks!
- Josh
>
>
>>
>> Capacitor C4 looks to be involved with the START-UP DRIVE signal
>> circuitry (which drives the relay) so the behavior I'm seeing makes
>> sense if C4 died and took a couple of things with it (or if something
>> else died and took C4 with it).
>>
>> Here's where it gets kind of odd -- I spent some time testing diodes
>> and transistors in the related area near C4 and while doing so I
>> noticed that there are four diodes (D1-D4) listed on the schematic
>> that are missing from my board. "Missing" as in someone clipped them
>> out at some point -- there are just nubs of the leads left. I'm not
>> sure why this would have been done, but there were a number of ECOs
>> applied to this board (a few wires and resistors added) and I don't
>> want to assume that if I just put four new diodes in that it won't
>> cause other problems. Anyone know if there were other revision
>> levels of the bias/interface board that would have done away with
>> these diodes? Anyone have an H7140 they can easily crack open to
>> compare? (It's actually relatively easy to get to, if you can get to
>> the
>> supply...)
>>
>> Thanks as always,
>> Josh
On Oct 10, 2015, at 4:15 AM, Mattis Lind
<mattislind at gmail.com> wrote:
2015-10-10 5:42 GMT+02:00 Josh Dersch <derschjo at gmail.com
<mailto:derschjo at gmail.com>>:
Hey all --
First of all I haven't poked around in the PSU of my 11/44 since it
worked fine when powered up. But the design of the H7140 is a lot
similar to the design of the H7104, the PSU of the VAX-11/750 which I
worked quite a lot with.
http://www.datormuseum.se/computers/digital-equipment-corporation/vax-
11-750
<http://www.datormuseum.se/computers/digital-equipment-corporation/vax
-11-750>
> Once again, I find myself in over my head debugging a power supply,
> this time an H7140 from a PDP-11/44. Here's the skinny:
>
> I examined the supply physically before experimenting and found a
> capacitor on the Bias/Interface board that was leaking, bursting and
> rather burned-out looking (not a great sign) -- this is capacitor C4
> in the printsets on Bitsavers (
> http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/1144/MP008
> 97_11X44sys_Dec79.pdf) Everything else looked OK physically; I
> replaced the obviously bad capacitor at C4.
>
> When power is applied (plugged in, breaker switch flipped to "On")
> the relay does not click - based on my readings of the manuals this
> should happen after the bias voltages are up to spec. I measure
> 308VDC on the lugs on the top of the memory board, so that's at least Getting
to other points to test voltages is a bit more difficult,
especially with those high voltages in the way, what a nice design :).
The previous owner said that it happens that the relays get stuck. The
relay is there to limit the inrush current so when it clicks it
bypasses a couple of power resistors. Regardless relay state you will
have the full voltage over the capacitors. (at least this is the case
in the H7104). If the relay get stuck then the power resistors get
very hot. The relay drive circuit detects that the voltage is high enough then Maybe something in this circuitry is bad. In this
case you could force
it to on but then I think you should power it from a variac
Thanks. I should have mentioned, but I tested out the relay and it?s not stuck
and seems to be working fine. It definitely looks like the relay control circuitry
is not running properly.
Switching the front panel switch to
"Local" (or any other position)
has no effect -- no fans, no LEDs, nothing. I've double-checked all
the wiring and everything looks OK.
Have you verified that you have the 12V BIAS voltage? If not you could
probably generate the 12V BIAS voltage using a lab power supply just
to see if the main switcher is working properly.
I used an insulation transformer and a variac and then forced the
relay drive to on. In the H7104 the same circuitry also enabled the
main switcher so unless I did this there were no fun at all. I
supplied 12V using a bench supply. It made it possible to check
everything was working ok without any high voltages.
10:41 a.m.
l?rdag 10 oktober 2015 skrev Josh Dersch <derschjo at gmail.com>:
worked
a
see
Looking yet another time at the schematic it is evident that a lot of
signal is relying on E5 collector beeing low. If the monitor circuit is
broken or not high enough voltage in (since you are running it off a
variac) you will not have this signal. To test I would ground this and run
it with a variac.
/Mattis
On Oct 10, 2015, at 4:15 AM, Mattis Lind
<mattislind at gmail.com
<javascript:;>> wrote:
2015-10-10 5:42 GMT+02:00 Josh Dersch <derschjo at gmail.com <javascript:;>
<mailto:derschjo at gmail.com <javascript:;>>>:
Hey all --
First of all I haven't poked around in the PSU of my 11/44 since it fine when powered up. But the design of the H7140
is a lot similar to the
design of the H7104, the PSU of the VAX-11/750 which I worked quite a lot
with.
http://www.datormuseum.se/computers/digital-equipment-corporation/vax-11-750
<
http://www.datormuseum.se/computers/digital-equipment-corporation/vax-11-750
> Once again, I find myself in over my head debugging a power supply, this
> time an H7140 from a PDP-11/44. Here's the skinny:
>
> I examined the supply physically before experimenting and found a
> capacitor on the Bias/Interface board that was leaking, bursting and
rather
> burned-out looking (not a great sign) -- this
is capacitor C4 in the
> printsets on Bitsavers (
>
http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/1144/MP00897_11X…
)
> Everything else looked OK physically; I
replaced the obviously bad
> capacitor at C4.
>
> When power is applied (plugged in, breaker switch flipped to "On") the
> relay does not click - based on my readings of the manuals this should
> happen after the bias voltages are up to spec. I measure 308VDC on the
> lugs on the top of the memory board, so that's at least something
working.
Getting
to other points to test voltages is a bit more difficult,
especially with those high voltages in the way, what a nice design :).
The previous owner said that it happens that the relays get stuck. The
relay is there to limit the inrush current so when it clicks it bypasses couple of power resistors. Regardless relay state
you will have the full
voltage over the capacitors. (at least this is the case in the H7104). If
the relay get stuck then the power resistors get very hot. The relay
drive
circuit detects that the voltage is high enough
then turns on the relay.
Maybe something in this circuitry is bad. In this case you could force it
to on but then I think you should power it from a variac
Thanks. I should have mentioned, but I tested out the relay and it?s not
stuck and seems to be working fine. It definitely looks like the relay
control circuitry is not running properly.
> Switching the front panel switch to "Local" (or any other position) has
no
effect --
no fans, no LEDs, nothing. I've double-checked all the wiring
and everything looks OK.
Have you verified that you have the 12V BIAS voltage? If not you could
probably generate the 12V BIAS voltage using a lab power supply just to if the main switcher is working properly.
I used an insulation transformer and a variac and then forced the relay
drive to on. In the H7104 the same circuitry also enabled the main
switcher
so unless I did this there were no fun at all. I
supplied 12V using a
bench
supply. It made it possible to check everything
was working ok without
any
high voltages.
Interesting idea, I?ll look into that. Thanks! - Josh
>
> Capacitor C4 looks to be involved with the START-UP DRIVE signal
circuitry
> (which drives the relay) so the behavior
I'm seeing makes sense if C4
died
> and took a couple of things with it (or if
something else died and took
C4
> with it).
>
> Here's where it gets kind of odd -- I spent some time testing diodes and
> transistors in the related area near C4 and while doing so I noticed
that
> there are four diodes (D1-D4) listed on the
schematic that are missing
from
> my board. "Missing" as in someone
clipped them out at some point --
there
> are just nubs of the leads left. I'm not
sure why this would have been
> done, but there were a number of ECOs applied to this board (a few wires
> and resistors added) and I don't want to assume that if I just put four
new
> diodes in that it won't cause other
problems. Anyone know if there were
> other revision levels of the bias/interface board that would have done
away
> with these diodes? Anyone have an H7140 they
can easily crack open to
> compare? (It's actually relatively easy to get to, if you can get to
the
> supply...)
>
> Thanks as always,
> Josh
3361
days inactive
3361
days old
7 comments
4 participants
participants (4)
-
cube1＠charter.net -
derschjo＠gmail.com -
mattislind＠gmail.com -
robert.jarratt＠ntlworld.com