Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread Adrian Graham via cctalk 

> On 20 Aug 2017, at 23:20, Chuck Guzis via cctalk  
> wrote:
> 
> On 08/20/2017 12:12 PM, Brent Hilpert via cctalk wrote:
> 
>> If the transformer were faulty and heating up internally, it would seem 
>> unlikely that it would cool off that quickly to recover, IME it takes some 
>> time for a transformer to cool off.
> 
> I have an open-frame linear PSU that started behaving that way.  Turned
> out to be a current-sense resistor with a bad internal connection.  As
> things warmed up, the resistance would rise until the current overload
> IC kicked it and shut things down.   It was pretty frustrating because
> the entire time, the output looked pretty stable.
> 
> I don't know if that's what's going on here, however.

There’s only 10 resistors in the whole PSU so it wouldn’t take long to replace 
them all. The problem could very well be thermal, today hasn’t been as warm as 
last week when I was testing it to shutdown. Freeze spray would hopefully 
confirm that.

Cheers,

—
Adrian/Witchy
Binary Dinosaurs - Celebrating Computing History from 1972 onwards

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread Chuck Guzis via cctalk 
On 08/20/2017 12:12 PM, Brent Hilpert via cctalk wrote:

> If the transformer were faulty and heating up internally, it would seem 
> unlikely that it would cool off that quickly to recover, IME it takes some 
> time for a transformer to cool off.

I have an open-frame linear PSU that started behaving that way.  Turned
out to be a current-sense resistor with a bad internal connection.  As
things warmed up, the resistance would rise until the current overload
IC kicked it and shut things down.   It was pretty frustrating because
the entire time, the output looked pretty stable.

I don't know if that's what's going on here, however.

--Chuck

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread Adrian Graham via cctalk 
>> 
>> Any clues appreciated. It’d be nice to feed the 6VAC input from another 
>> source but I’m not sure my VARIAC will go that low.
> 
> 
> The gain pin is presenting the output of the error amplifier, an increase 
> there is what you would expect as the output V falls, as the difference 
> between the ref and target V increases.
> It's 'trying harder' to raise the output V to correct the error.
> It implies that the reference and the error amplifier are functioning.

OK, I can see that.

> 
> "6VAC outputs do go a bit erratic" is not a helpful description.

I thought they dropped continually but they’re just constantly adjusting around 
6VAC. Annoyingly I’ve just run the whole system for the last 40 minutes and 
while the troublesome supply has dipped below 5V at times it hasn’t collapsed. 
I’ve been formatting floppies, copying files between floppies and rebooting. 
Only now has floppy access started to fail at 4.8V but the machine itself still 
runs. Screen output flickers though, but nothing catastrophic like the other 
day.

> 
> A wide range of stepdown transformers  .. 8V, 10V, 12V, 18V, 24V ..  could be 
> used in conjunction with your variac to get 6VAC for an alternate feed.
> 
> If you have a variable DC supply of adequate current you can feed approx. 6V 
> * 1.4 = 8.4VDC into the 6VAC input instead.
> 

I’ve got a couple of 5A bench supplies if necessary.

> Is the failure load-level (current-draw) related?:
>   Does the out V remain stable if the supply is unloaded or very lightly 
> loaded?
>   Does it take longer to drop at a lesser load?
> If so it's likely thermal-related.

V out is stable with no load, as soon as the ST is turned off. I could use it 
to run the floppy drive but that’s such a low load I don’t think it would cause 
failure. Worth a try I guess.

> Is anything heating up unduly?
> 

I can’t tell without the aforementioned jury-rigging extra wiring, in normal 
usage it looks like this - http://www.binarydinosaurs.co.uk/atariSTPSU-2.jpg

Cheers!

—
Adrian/Witchy
Binary Dinosaurs - Celebrating Computing History from 1972 onwards

massive amt. of SAS for pc sale bookset

2017-08-20 Thread Ed Sharpe via cctalk 
 of SAS .massive amt. of SAS books for pc sale bookset.. if you need reply off 
list thanks Ed # www.smecc.org

Sent from AOL Mobile Mail

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread Brent Hilpert via cctalk 
On 2017-Aug-20, at 4:45 AM, Adrian Graham via cctalk wrote:
> I think I’ve mentioned this PSU before but the question I have might be 
> applicable to other cheap switchers. This lump for the original Atari 520ST 
> is run by an NE5561N control chip with a D45H1 switching transistor. It’s 
> supplied by a multi-tap transformer giving 2x2 feeds of 6VAC and 14VAC with 
> an eventual output of 5V@3A, 12V@30mA, -12V@30mA.
> 
> This one will run under load for around 10 minutes then the 5V rail will 
> gradually collapse over the next few minutes. Turn it off and leave for a 
> minute or so and it’s back to normal, repeat as above.
> 
> Unfortunately there’s no schematic online but I’ve done a mix photo of the 
> control circuits:
> 
> http://www.binarydinosaurs.co.uk/atariPSU1Hybrid.jpg 
>  
> 
> The 4700uF cap in the centre is on the output stage so I changed that 
> yesterday which just makes the eventual collapse longer.
> 
> Could the actual transformer lump break down over time and recover that 
> quickly? Its 6VAC outputs do go a bit erratic. Also I measured the GAIN input 
> on the NE5561N pin 4 and during the collapse it goes over twice what it is 
> when the 5V rail is stable (7V instead of around 3.4V). I have another 
> running supply to measure against.
> 
> Any clues appreciated. It’d be nice to feed the 6VAC input from another 
> source but I’m not sure my VARIAC will go that low.


The gain pin is presenting the output of the error amplifier, an increase there 
is what you would expect as the output V falls, as the difference between the 
ref and target V increases.
It's 'trying harder' to raise the output V to correct the error.
It implies that the reference and the error amplifier are functioning.

"6VAC outputs do go a bit erratic" is not a helpful description.

A wide range of stepdown transformers  .. 8V, 10V, 12V, 18V, 24V ..  could be 
used in conjunction with your variac to get 6VAC for an alternate feed.

If you have a variable DC supply of adequate current you can feed approx. 6V * 
1.4 = 8.4VDC into the 6VAC input instead.

Is the failure load-level (current-draw) related?:
Does the out V remain stable if the supply is unloaded or very lightly 
loaded?
Does it take longer to drop at a lesser load?
If so it's likely thermal-related.
Is anything heating up unduly?

If the transformer were faulty and heating up internally, it would seem 
unlikely that it would cool off that quickly to recover, IME it takes some time 
for a transformer to cool off.

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread Mike Stein via cctalk 
Well, if we're going to nitpick it's _baling_ wire as in tying up bales of hay; 
bailing is for leaky boats.

m
- Original Message - 
From: "drlegendre . via cctalk" 
To: "Adrian Graham" ; "General Discussion: On-Topic 
and Off-Topic Posts" 
Sent: Sunday, August 20, 2017 2:01 PM
Subject: Re: Atari PSU with collapsing 5V rail


Arrgh! /Jerry rig/, not Jury rig! Jury rigging is something entirely
different..

The former comes from WWII era slang, when German soldiers were called
'Jerries' (among other things); see Jerrycan for instance. As has often
been the case, as the war drew to a close and the supply chains broke down,
everything needed to run the army dried up, hence the need for quite a few
"field expedient" (read: improvised) repairs to machinery and weapons.

And I don't think they even had duct tape in those days, did they? More of
a bailing wire era, one would suspect..

On Sun, Aug 20, 2017 at 12:15 PM, Adrian Graham via cctalk <
cctalk@classiccmp.org> wrote:

>
> > On 20 Aug 2017, at 16:32, Mattis Lind  wrote:
> >
> >
> >
> > söndag 20 augusti 2017 skrev Adrian Graham via cctalk <
> cctalk@classiccmp.org >:
> > Hi folks,
> >
> > I think I’ve mentioned this PSU before but the question I have might be
> applicable to other cheap switchers. This lump for the original Atari 520ST
> is run by an NE5561N control chip with a D45H1 switching transistor. It’s
> supplied by a multi-tap transformer giving 2x2 feeds of 6VAC and 14VAC with
> an eventual output of 5V@3A, 12V@30mA, -12V@30mA.
> >
> > This one will run under load for around 10 minutes then the 5V rail will
> gradually collapse over the next few minutes. Turn it off and leave for a
> minute or so and it’s back to normal, repeat as above.
> >
> > Heat related?  Try freeze spray to check if it recovers or stays working
> longer.
>
> I need to jury rig something with a breadboard to allow me to run it
> outside the enclosure, in normal usage it’s solder side up with the
> components covered. I can’t remove the transformer lump because it’s sealed
> in resin. They really didn’t want people to attempt to fix these things :)
>
>
> —
> Adrian/Witchy
> Binary Dinosaurs - Celebrating Computing History from 1972 onwards
>
>
>

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread drlegendre . via cctalk 
I must admit, by all appearances I've fallen for a false etymology.. at
least so far as having origins in WWII slang. Depending on how you view it,
the origin of 'jerry-rigged' is either much older +or+ slightly newer..

Here's an interesting and somewhat detailed discussion:
https://english.stackexchange.com/questions/132868/jury-rigged-or-jerry-rigged/132919

As for the PSU, that drifting gain voltage seems to be a major clue. Where
does this voltage track in the known-good unit? Have you also verified that
all of the precision voltage references / zeners / etc. are themselves
stable and not drifting?

Is the voltage generated by the controller chip, or supplied to the chip
from an external reference?



On Sun, Aug 20, 2017 at 1:24 PM, Hagstrom, Paul  wrote:

> As far as I know, the relevant ('temporary/improvised') concept is
> generally accepted to be (or at least originally to have been)
> "jury-rigged."
>
> https://en.oxforddictionaries.com/definition/jury-rigged
>
> http://archives.cjr.org/language_corner/the_jury_is_in.php
>
> Nothing to do with WWII, though perhaps the convenient near-homonym led to
> a separate, later usage through mis-hearing the original usage.  At best
> both are "correct" for the concept, conservatively/prescriptively only
> jury-rigged is.
>
> We now return to troubleshooting the Atari PSU, already in progress.
>
>
> > On Aug 20, 2017, at 2:01 PM, drlegendre . via cctalk <
> cctalk@classiccmp.org> wrote:
> >
> > Arrgh! /Jerry rig/, not Jury rig! Jury rigging is something entirely
> > different..
> >
> > The former comes from WWII era slang, when German soldiers were called
> > 'Jerries' (among other things); see Jerrycan for instance. As has often
> > been the case, as the war drew to a close and the supply chains broke
> down,
> > everything needed to run the army dried up, hence the need for quite a
> few
> > "field expedient" (read: improvised) repairs to machinery and weapons.
> >
> > And I don't think they even had duct tape in those days, did they? More
> of
> > a bailing wire era, one would suspect..
> >
> > On Sun, Aug 20, 2017 at 12:15 PM, Adrian Graham via cctalk <
> > cctalk@classiccmp.org> wrote:
> >
> >>
> >>> On 20 Aug 2017, at 16:32, Mattis Lind  wrote:
> >>>
> >>>
> >>>
> >>> söndag 20 augusti 2017 skrev Adrian Graham via cctalk <
> >> cctalk@classiccmp.org >:
> >>> Hi folks,
> >>>
> >>> I think I’ve mentioned this PSU before but the question I have might be
> >> applicable to other cheap switchers. This lump for the original Atari
> 520ST
> >> is run by an NE5561N control chip with a D45H1 switching transistor.
> It’s
> >> supplied by a multi-tap transformer giving 2x2 feeds of 6VAC and 14VAC
> with
> >> an eventual output of 5V@3A, 12V@30mA, -12V@30mA.
> >>>
> >>> This one will run under load for around 10 minutes then the 5V rail
> will
> >> gradually collapse over the next few minutes. Turn it off and leave for
> a
> >> minute or so and it’s back to normal, repeat as above.
> >>>
> >>> Heat related?  Try freeze spray to check if it recovers or stays
> working
> >> longer.
> >>
> >> I need to jury rig something with a breadboard to allow me to run it
> >> outside the enclosure, in normal usage it’s solder side up with the
> >> components covered. I can’t remove the transformer lump because it’s
> sealed
> >> in resin. They really didn’t want people to attempt to fix these things
> :)
> >>
> >>
> >> —
> >> Adrian/Witchy
> >> Binary Dinosaurs - Celebrating Computing History from 1972 onwards
> >>
> >>
> >>
>
>

RE: DEC VT125 on Schpock in Birmingham, UK

2017-08-20 Thread Rob Jarratt via cctalk 
> -Original Message-
> From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Rob Jarratt
> via cctalk
> Sent: 19 August 2017 23:33
> To: 'Paul Anderson' ; 'General Discussion: On-Topic and
> Off-Topic Posts' ; 'Pete Hollobon'
> 
> Subject: RE: DEC VT125 on Schpock in Birmingham, UK
> 
> Never heard of that site before, always wanted a VT125 and certainly
> reachable from here. Will investigate!
> 

Well, that didn't go too well.

I made the offer of the asking price. I got no reply, no acknowledgement, no 
acceptance or rejection. Then today someone else made an offer which seems to 
have been accepted. When I asked why I had not even had a response I was told 
he wasn't prepared to wait for several weeks (I had said I might not be able to 
collect for a week or two), and I had not been given any opportunity to discuss 
it. I could see he had accepted someone else's offer, and he then promptly 
asked me if I would beat his highest offer.

After accepting someone's offer it doesn't seem too right to then ask if 
someone else will beat it. Perhaps not the kind of seller to deal with I think.

So, although I have wanted a VT125 for a long time, it looks like I am not 
going to get one :-(

Regards

Rob

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread Hagstrom, Paul via cctalk 
As far as I know, the relevant ('temporary/improvised') concept is generally 
accepted to be (or at least originally to have been) "jury-rigged."

https://en.oxforddictionaries.com/definition/jury-rigged

http://archives.cjr.org/language_corner/the_jury_is_in.php

Nothing to do with WWII, though perhaps the convenient near-homonym led to a 
separate, later usage through mis-hearing the original usage.  At best both are 
"correct" for the concept, conservatively/prescriptively only jury-rigged is.

We now return to troubleshooting the Atari PSU, already in progress.


> On Aug 20, 2017, at 2:01 PM, drlegendre . via cctalk  
> wrote:
> 
> Arrgh! /Jerry rig/, not Jury rig! Jury rigging is something entirely
> different..
> 
> The former comes from WWII era slang, when German soldiers were called
> 'Jerries' (among other things); see Jerrycan for instance. As has often
> been the case, as the war drew to a close and the supply chains broke down,
> everything needed to run the army dried up, hence the need for quite a few
> "field expedient" (read: improvised) repairs to machinery and weapons.
> 
> And I don't think they even had duct tape in those days, did they? More of
> a bailing wire era, one would suspect..
> 
> On Sun, Aug 20, 2017 at 12:15 PM, Adrian Graham via cctalk <
> cctalk@classiccmp.org> wrote:
> 
>> 
>>> On 20 Aug 2017, at 16:32, Mattis Lind  wrote:
>>> 
>>> 
>>> 
>>> söndag 20 augusti 2017 skrev Adrian Graham via cctalk <
>> cctalk@classiccmp.org >:
>>> Hi folks,
>>> 
>>> I think I’ve mentioned this PSU before but the question I have might be
>> applicable to other cheap switchers. This lump for the original Atari 520ST
>> is run by an NE5561N control chip with a D45H1 switching transistor. It’s
>> supplied by a multi-tap transformer giving 2x2 feeds of 6VAC and 14VAC with
>> an eventual output of 5V@3A, 12V@30mA, -12V@30mA.
>>> 
>>> This one will run under load for around 10 minutes then the 5V rail will
>> gradually collapse over the next few minutes. Turn it off and leave for a
>> minute or so and it’s back to normal, repeat as above.
>>> 
>>> Heat related?  Try freeze spray to check if it recovers or stays working
>> longer.
>> 
>> I need to jury rig something with a breadboard to allow me to run it
>> outside the enclosure, in normal usage it’s solder side up with the
>> components covered. I can’t remove the transformer lump because it’s sealed
>> in resin. They really didn’t want people to attempt to fix these things :)
>> 
>> 
>> —
>> Adrian/Witchy
>> Binary Dinosaurs - Celebrating Computing History from 1972 onwards
>> 
>> 
>>

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread drlegendre . via cctalk 
Arrgh! /Jerry rig/, not Jury rig! Jury rigging is something entirely
different..

The former comes from WWII era slang, when German soldiers were called
'Jerries' (among other things); see Jerrycan for instance. As has often
been the case, as the war drew to a close and the supply chains broke down,
everything needed to run the army dried up, hence the need for quite a few
"field expedient" (read: improvised) repairs to machinery and weapons.

And I don't think they even had duct tape in those days, did they? More of
a bailing wire era, one would suspect..

On Sun, Aug 20, 2017 at 12:15 PM, Adrian Graham via cctalk <
cctalk@classiccmp.org> wrote:

>
> > On 20 Aug 2017, at 16:32, Mattis Lind  wrote:
> >
> >
> >
> > söndag 20 augusti 2017 skrev Adrian Graham via cctalk <
> cctalk@classiccmp.org >:
> > Hi folks,
> >
> > I think I’ve mentioned this PSU before but the question I have might be
> applicable to other cheap switchers. This lump for the original Atari 520ST
> is run by an NE5561N control chip with a D45H1 switching transistor. It’s
> supplied by a multi-tap transformer giving 2x2 feeds of 6VAC and 14VAC with
> an eventual output of 5V@3A, 12V@30mA, -12V@30mA.
> >
> > This one will run under load for around 10 minutes then the 5V rail will
> gradually collapse over the next few minutes. Turn it off and leave for a
> minute or so and it’s back to normal, repeat as above.
> >
> > Heat related?  Try freeze spray to check if it recovers or stays working
> longer.
>
> I need to jury rig something with a breadboard to allow me to run it
> outside the enclosure, in normal usage it’s solder side up with the
> components covered. I can’t remove the transformer lump because it’s sealed
> in resin. They really didn’t want people to attempt to fix these things :)
>
>
> —
> Adrian/Witchy
> Binary Dinosaurs - Celebrating Computing History from 1972 onwards
>
>
>

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread Adrian Graham via cctalk 

> On 20 Aug 2017, at 16:32, Mattis Lind  wrote:
> 
> 
> 
> söndag 20 augusti 2017 skrev Adrian Graham via cctalk  >:
> Hi folks,
> 
> I think I’ve mentioned this PSU before but the question I have might be 
> applicable to other cheap switchers. This lump for the original Atari 520ST 
> is run by an NE5561N control chip with a D45H1 switching transistor. It’s 
> supplied by a multi-tap transformer giving 2x2 feeds of 6VAC and 14VAC with 
> an eventual output of 5V@3A, 12V@30mA, -12V@30mA.
> 
> This one will run under load for around 10 minutes then the 5V rail will 
> gradually collapse over the next few minutes. Turn it off and leave for a 
> minute or so and it’s back to normal, repeat as above.
> 
> Heat related?  Try freeze spray to check if it recovers or stays working 
> longer. 

I need to jury rig something with a breadboard to allow me to run it outside 
the enclosure, in normal usage it’s solder side up with the components covered. 
I can’t remove the transformer lump because it’s sealed in resin. They really 
didn’t want people to attempt to fix these things :)


—
Adrian/Witchy
Binary Dinosaurs - Celebrating Computing History from 1972 onwards

Re: Atari PSU with collapsing 5V rail

2017-08-20 Thread Mattis Lind via cctalk 
söndag 20 augusti 2017 skrev Adrian Graham via cctalk :

> Hi folks,
>
> I think I’ve mentioned this PSU before but the question I have might be
> applicable to other cheap switchers. This lump for the original Atari 520ST
> is run by an NE5561N control chip with a D45H1 switching transistor. It’s
> supplied by a multi-tap transformer giving 2x2 feeds of 6VAC and 14VAC with
> an eventual output of 5V@3A, 12V@30mA, -12V@30mA.
>
> This one will run under load for around 10 minutes then the 5V rail will
> gradually collapse over the next few minutes. Turn it off and leave for a
> minute or so and it’s back to normal, repeat as above.


Heat related?  Try freeze spray to check if it recovers or stays working
longer.


/Mattis

Re: Anyone need an M7389 card (for an LA30)?

2017-08-20 Thread Fritz Mueller via cctalk 

> On Aug 19, 2017, at 10:10 PM, Mattis Lind  wrote:
> 
> BTW. I have LC11 manual and drawings. But they are for the older M791. At 
> least a bit helpful. Not scanned yet.

I'd be very interested to see those once scanned.  I haven't gotten to the 
interface card yet; so far I've just been working on cleanup and checkout of 
the LA30 itself.  Reformed the power supply electrolytics and replaced the PCB 
cap in the ferro-resonant circuit.  Checked that all the pins on the print head 
are free and functioning.  So, so far so good.  Nice to make contact with the 
other members of the LA30 club!

   cheers,
   --FritzM.

Atari PSU with collapsing 5V rail

2017-08-20 Thread Adrian Graham via cctalk 
Hi folks,

I think I’ve mentioned this PSU before but the question I have might be 
applicable to other cheap switchers. This lump for the original Atari 520ST is 
run by an NE5561N control chip with a D45H1 switching transistor. It’s supplied 
by a multi-tap transformer giving 2x2 feeds of 6VAC and 14VAC with an eventual 
output of 5V@3A, 12V@30mA, -12V@30mA.

This one will run under load for around 10 minutes then the 5V rail will 
gradually collapse over the next few minutes. Turn it off and leave for a 
minute or so and it’s back to normal, repeat as above.

Unfortunately there’s no schematic online but I’ve done a mix photo of the 
control circuits:

http://www.binarydinosaurs.co.uk/atariPSU1Hybrid.jpg 
 

The 4700uF cap in the centre is on the output stage so I changed that yesterday 
which just makes the eventual collapse longer.

Could the actual transformer lump break down over time and recover that 
quickly? Its 6VAC outputs do go a bit erratic. Also I measured the GAIN input 
on the NE5561N pin 4 and during the collapse it goes over twice what it is when 
the 5V rail is stable (7V instead of around 3.4V). I have another running 
supply to measure against.

Any clues appreciated. It’d be nice to feed the 6VAC input from another source 
but I’m not sure my VARIAC will go that low.

—
Adrian/Witchy
Binary Dinosaurs - Celebrating Computing History from 1972 onwards

RE: Anyone need an M7389 card (for an LA30)?

2017-08-20 Thread Henk Gooijen via cctalk 


Van: Mattis Lind via cctalk
Verzonden: zondag 20 augustus 2017 07:10
Aan: Fritz Mueller; General Discussion: On-Topic and 
Off-Topic Posts
Onderwerp: Re: Anyone need an M7389 card (for an LA30)?

lördag 19 augusti 2017 skrev Fritz Mueller via cctalk :
> On 08/17/2017 12:54 PM, Noel Chiappa via cctalk wrote:
>
>> Anyone out there have an LA30? :-)
>
> For future reference, I am also working on an LA30 at the moment.  I think
> Mattis has restored one as well?

Yes. That's right. Have a LA30P with a LC11. BTW. I have LC11 manual and
drawings. But they are for the older M791. At least a bit helpful. Not
scanned yet.

> Mine is a P, and I have the matching M7910 to go with it, so no need for
> an M7389 here (sounds like Henk really wanted it anyway!

Henk got my second LA30. But one need a M7731 board as well to make it
serial. The M7389 alone is not enough unfortunately.



Yup, and I still am very happy that I decided to drive in total some
3200 km “just” to pick up one LA30. It was worth the long trip
and stay in 3 hotels, because Mattis also gave me a tour along his
collection. Fantastic  and very cool things I had never seen before !

Good to know that I need to look out for an other board! I quickly
responded to Noel’s offer, without knowing that I needed yet an
other module. But if I had skipped Noel’s offer and found the M7731
(in the future) then I would have the “problem” of the missing M7389 …
Collecting is a matter of time and patience. There is no joy in getting
everything “overnight”.

Henk

Re: DCC-116 E / DATA GENERAL NOVA 2/10 / Nixdorf 620 - Restoring and restarting

2017-08-20 Thread Brent Hilpert via cctalk 
On 2017-Aug-20, at 12:08 AM, Brent Hilpert via cctalk wrote:
> On 2017-Aug, at 12:10 PM, Dominique Carlier via cctalk wrote:
>>> 
>>> Question: a faulty voltage regulator can behave in this way? I always 
>>> thought it worked or it did not work, but not between the two states 
>>> depending on the charge.
> 
> (In answer to the question, yes, a faulty regulator can produce 'in-between' 
> output voltage.)


Should modify that answer a little: a regulator like this can, not just if 
faulty, but also by design intention, produce an 'in-between' output voltage, 
as per the functioning of the current-limit circuitry.

Re: DCC-116 E / DATA GENERAL NOVA 2/10 / Nixdorf 620 - Restoring and restarting

2017-08-20 Thread Brent Hilpert via cctalk 
On 2017-Aug-19, at 12:10 PM, Dominique Carlier via cctalk wrote:
> Maybe it's better to give us all the useful information these power supplies, 
> moreover it might be useful to other people with the same computer.
> 
> An overall bloc diagram of the D-116 power supply including G1 and G2.
> http://www.zeltrax.com/classiccmp_forum/psu_overall_bloc_diagram.jpg
> 
> The complete schematics of the part of the power supply named G2.
> http://www.zeltrax.com/classiccmp_forum/g2_schematics.jpg
> 
> A drawing of the regulation board of the power supply G2 with the physical 
> locations of the components.
> http://www.zeltrax.com/classiccmp_forum/g2_regulator_board.jpg
> 
> The schematics of this regulation board.
> http://www.zeltrax.com/classiccmp_forum/g2_regulator_board_schematics.jpg
> 
> And a bit of literature concerning the principle of operation about the 
> regulation with this PSU (you will understand better why I am a little bit 
> lost ;-) This principle of regulation with a panoply of verification and 
> Protection systems everywhere is unusual for me)
> http://www.zeltrax.com/classiccmp_forum/psu_regulation_principe.jpg
> 
> I have already tried without the CPU board: same symptoms. Next step, try to 
> check the capacitors in operation.


>> Results of the observations:
>> - This is definitely the regulated +5V of the G2 power supply. More I add 
>> boards more the + 5v level goes down. +5v, +4.8v, +3.6v, +2.9v. It remains 
>> stable however with just the CPU and the three core memory boards, it 
>> becomes difficult for the power supply when I add boards in addition to 
>> these.
>> - This is definitely not a problem at the level of the Power Fail circuit.
>> - The big capacitors are not in fault (I rechecked twice).
>> - So this maybe a problem at the level of the regulation itself, the +5V 
>> balancing system ?
>> 
>> Question: a faulty voltage regulator can behave in this way? I always 
>> thought it worked or it did not work, but not between the two states 
>> depending on the charge.

(In answer to the question, yes, a faulty regulator can produce 'in-between' 
output voltage.)

As is typical for power supplies of this type and era, this power supply 
includes current limiting circuitry.

The current-limiting circuitry will throttle down the output voltage (not shut 
it off completely) as the output current draw goes above a design limit.
This would appear to fit the symptoms you describe.

The current-limiting circuitry works by placing a small-value resistor in the 
current path after the main regulator transistor(s) (aka pass transistors) but 
prior to the voltage-regulation sense point.
A transistor senses the voltage across this R.
As the output current increases, the voltage across the current-sense R 
increases, at some point the transistor starts to turn on, and the transistor 
is connected in such a way that as it turns on it reduces the drive to the pass 
transistors, throttling down the output voltage.

Arbitrarily using the "A2" heatsink half of the two +5 supplies in this power 
supply for component references, the current-sense R is comprised of a 
series-parallel circuit formed by the BE junctions of the 2 pass transistors 
(A2.Q1, A2.Q2), the two 0.1ohm Rs on the emitters of the pass transistors 
(A3.R10,A3.R11), the 47ohm Rs between B&E of those transistors, A3.R23, 
A3A1A1.R8, 376.R9, along with additional influence by 376.R8 and A3A1A1.R10.
The current sense transistor is inside the LM376 (see internal schematic), 
376.Q16 between pins 1 & 8, controlling the 1st-stage driver transistor 376.Q14.

There are various things that could go wrong on this circuitry.
Anything that upsets the current-sense resistance network to cause the net R to 
increase will lower the output current that can be drawn (that is, the current 
limiting circuitry will start kicking in too 'early').

A likely scenario is one of the pass transistors has failed open.
This would take out a parallel leg of the current-sense resistance.
All current would  be forced through the good pass transistor and it's emitter 
resistor, raising the current-sense voltage for a given output current.
The current-limiting circuitry would kick in at a lower current than the design 
intention.
This is beneficial inasmuch as it would work to save the good pass transistor.

The 0.1 ohm 9W emitter resistors are critical, although they're probably 
wirewound and fairly reliable unless quite overstressed.
One of these resistors being open would result in the same operation as an open 
pass transistor.
You'll have difficulty measuring them with accuracy but you could do some 
sanity checks for continuity around both the pass transistor circuit legs,
as well as checking the pass transistor BC/BE junctions.

(In principle, the 'proper' thing to do in this area is look at what the 
current-sense voltage is doing, but that requires knowing what the target V is. 
Could compare with the other half of the supply.)

None of this is to su