Re: DEC H7822 power supply

[Peter Coghlan via cctalk]

Hi Maciej,

Thanks for your input.

"Maciej W. Rozycki" wrote:
>
> Lying on a side would also permit leaking, I've seen an H7821 damaged in 
> storage that way.  Gravity only helps with the leads up.
>

I have lots of H7821s that were on their side for a few years and leaked a
lot but I also have H7822s that were stored the same way and did not show
any evidence of leaking until very recently.  I think I also have some
H7821s that were the right way up most of their lives and have leaked a
little.  It's getting hard to remember what happened to which :-(

>
> From experience Chemi-con SXF caps used with many DEC PSUs need to be 
> urgently replaced.  Other Chemi-con lines reported affected are LXF, SXE 
> and KME.  Products of the time from other manufacturers may be affected as 
> well.  I'd have to check what line were those that leaked in a Bel Power 
> PSU that I had to fix (I reckon you had a similar experience, right?).
>

I still have the leaky electrolytics I removed from the POWER-ONE PSU in my
Cisco IGS a while back.  I stored them with their leads up and goo seems to
be still oozing out of some of them despite their inactivity and orientation.
These ones are marked Nichicon PL(M) 4700uF/63V, 2200uF/16V and 330uF/35V and
also have markings like H8950, H9018 and H8946 - maybe these are date codes?
I also removed the smaller ones like 47uF/35V PF(M) H8952 for example but it
is less clear to me whether these were leaking too or just got leaked on by
the others.  There were only a few of them so I decided they were better out
than in.  They all have similar coloured brown sleeves like the faulty ones
in the DEC power supplies too.

There are also the leaky 10uF/35V axial electrolytics in my LK201 keyboard.
Those are in orange sleeves and marked "ESZ", whatever that is.  They have
date codes like 8612.  I thought this might be a widespread problem but
so far I have only found it in one keyboard.

>
> It was the composition of the electrolyte that was outright wrong, so I 
> doubt it's batch-related.
>

>
> Once the seal has broken I guess all odds are off.  I could imagine 
> capillary action to take effect.
>

Looks like I need to go back and recheck everything I thought wasn't leaking
last time I checked :-(

Thing is, to check them, they have to come out of the case and that involves
at least some change in orientation, except for contortionists...

>
> Heat dissipated by the cap itself under high ripple current never helps 
> and will surely speed up cap deterioration.  After all its service life 
> halvens with each 10°C temperature rise even with non-faulty parts.
>

When I was shopping for replacements, I was a bit alarmed to find that
the maximum specified "endurance" (whatever that is) I could find was
5000 hours.  This isn't much more than a long life incandescent light bulb.

>
> As a matter of interest what capacitance/voltage are those?  Are they of 
> the Chemi-con/SXF type too?
>

All the leaking ones in DEC H7821 and H7822 PSUs I have come across so far
are 1800uF/25V Chemicon with brown sleeves.  I think mine are all SXF
but I am not 100% sure of that.  There are lots of other electrolytic
capacitors in these power supplies but I've only looked closely at the
larger ones.  All of the reservoir capacitors attached to the mains bridge
rectifiers that I have seen look fine.  Maybe I need to go back and check
the smaller ones though :-(

I think I came across some LXF ones that seemed to be ok, I can't remember
where though.  I probably need to go find these and check them again :-(

Here's a thought.  Apart from the keyboard, all the ones I have seen that
are leaking are filtering the outputs of switch mode power supplies.  I
wonder does the higher frequency of the ripple they are dealing with have
a bearing on this?


I replaced the five leaking capacitors on the upper board in my H7822,
disconnected the input to the lower board and moved the LED connection to
the upper board.  The machine powered up nicely afterwards, the fans spun
and the green LED came on after a short delay.  However, the diagnostic
LEDs all come on and stay on so it appears the CPU is being made aware that
the lower board is not functioning, even though I don't need it.  I should
to do some comparisons with a H7821 and see if I can work around this.  Or
maybe I could fit some not quite to specification electrolytics from the
junk box on the lower board, just to keep it happy?

Regards,
Peter Coghlan.

>
>  Maciej
>

Re: cleaning up edge connectors

[Eric Smith via cctalk]

On Thu, Apr 28, 2022, 15:03 Peter Cetinski via cctalk 
wrote:

>
> TRS-80 guru Ian Mavric sells those gold connectors for the TRS-80.
>
> https://www.ebay.com/itm/164568343523 <
> https://www.ebay.com/itm/164568343523>
>

They're made by Sullins, and may be orderable from Digi-Key and other
distributors. I've bought them from Digi-Key in the past, but I think
Digi-Key may have stopped stocking them.

ASR 33 For Sale

[Marden Marshall via cctalk]

I’m moving and just don’t have enough room.

It is in great working condition having been professionally restored a few 
years back. The only issue is that someone dropped something onto the top cover 
and cracked the clear plastic window.

I’m looking to get $800.00 for it. Local pickup only (Boston area)

Thanks,

-Mardy

ma...@me.com 
(603) 264-1234

Re: DEC H7822 power supply

[Maciej W. Rozycki via cctalk]

On Tue, 3 May 2022, Peter Coghlan via cctalk wrote:

> > Would the system have been possibly stored upside down sometime?
> >
> 
> I don't think so.  It may have spent some time lying on it's side due to
> deteriorating rubber feet and for ease of access and but I can't see any
> reason for it ever being upside down.  Once I discovered this issue a few
> years ago, I checked all my power supplies, removed any leaking capacitors
> and changed to storing the machines the right way up in a vertical stack,
> with newspapers between them in place of the rubber feet.  I hoped this would
> prevent any capacitors which hadn't shown any signs of leaking from starting
> to leak.  (Now whichever machine I want to work on always seems to be at the
> bottom of the stack...)

 Lying on a side would also permit leaking, I've seen an H7821 damaged in 
storage that way.  Gravity only helps with the leads up.

> >  These nasty caps do leak even while in storage (and even if never used, 
> > not even soldered ever, according to one source, a repair professional).
> >
> 
> They are nasty and devious.  In my case, the ones that have been stored in
> any orientation but not used much seem to have fared better.  I only started
> using this machine with the H7822 for extended periods for the first time a
> few months ago.  One of the reasons I started using it more is because I
> thought it was immune to the leaky capacitor problem!  It never saw any
> serious use before that, even when it was new.

 From experience Chemi-con SXF caps used with many DEC PSUs need to be 
urgently replaced.  Other Chemi-con lines reported affected are LXF, SXE 
and KME.  Products of the time from other manufacturers may be affected as 
well.  I'd have to check what line were those that leaked in a Bel Power 
PSU that I had to fix (I reckon you had a similar experience, right?).

> I have at least two machines with H7822 power supplies.  Even though they
> have capacitors that look the same as the ones in the H7821, the ones in
> the H7822 power supplies didn't seem to be showing any signs of leaking
> when I examined them some time ago so I thought they might be from a batch
> that was unaffected by the problem.  It seems that this was not true :-(

 It was the composition of the electrolyte that was outright wrong, so I 
doubt it's batch-related.

> I unsoldered the other eight similar capacitors (four one each board) from
> the H7822 yesterday evening.  I found a small amount of leakage under most
> of them but it was was only evident after they were removed from the board.

 Yes, it's been a common case.

> In general, there was less damage visible under the ones on the lower board
> with leads facing down oddly enough.  I thought one of the capacitors from
> the upper board had not leaked at all.  I left the removed capacitors
> standing on the bench overnight with their leads upwards and they all have
> some signs of leakage visible on them today.  It's hard to draw any
> conclusions.

 Once the seal has broken I guess all odds are off.  I could imagine 
capillary action to take effect.

> The capacitor from the upper board that leaked enough for me to notice it
> might be under greater stress when operating than the others.  I think the
> same capacitor in the H7821 power supplies seems to leak more in those too.

 Heat dissipated by the cap itself under high ripple current never helps 
and will surely speed up cap deterioration.  After all its service life 
halvens with each 10°C temperature rise even with non-faulty parts.

> I don't have enough spare capacitors to replace the four on the lower
> board.  I am going to leave those out, leave the input lead to that board
> unplugged and plug the green LED into the upper board.  I hope it will then
> behave just like a H7821.  There won't be any power to the front disk drive
> connector but I am not using that so it doesn't matter unless the "power good"
> output is affected, in which case I will have to think of something else.

 As a matter of interest what capacitance/voltage are those?  Are they of 
the Chemi-con/SXF type too?

  Maciej

Re: DEC H7822 power supply

[Peter Coghlan via cctalk]

"Maciej W. Rozycki" wrote:
>On Mon, 2 May 2022, Peter Coghlan via cctalk wrote:
>
>> Thankfully, it doesn't seem to have been there long and didn't get a chance
>> to spread around the board.  Bizarrely this capacitor has it's legs pointing
>> upwards and managed to leak while there are similar capacitors on the other
>> board with their legs pointing downwards which don't seem to have leaked 
>> (yet?).
>
> Would the system have been possibly stored upside down sometime?
>

I don't think so.  It may have spent some time lying on it's side due to
deteriorating rubber feet and for ease of access and but I can't see any
reason for it ever being upside down.  Once I discovered this issue a few
years ago, I checked all my power supplies, removed any leaking capacitors
and changed to storing the machines the right way up in a vertical stack,
with newspapers between them in place of the rubber feet.  I hoped this would
prevent any capacitors which hadn't shown any signs of leaking from starting
to leak.  (Now whichever machine I want to use always seems to be at the
bottom of the stack...)

>
>  These nasty caps do leak even while in storage (and even if never used, 
> not even soldered ever, according to one source, a repair professional).
>

In my case, the ones that have been stored in any orientation but not used
much seem to have fared better.  I only started using this machine with the
H7822 for extended periods for the first time a few months ago.  One of the
reasons I started using it more is because I thought it was immune to the
leaky capacitor problem!  It never saw any serious use before that, even
when it was new.

I have at least two machines with H7822 power supplies.  Even though they
have capacitors that look the same as the ones in the H7821, the ones in
the H7822 power supplies didn't seem to be showing any signs of leaking
when I examined them some time ago so I thought they might be from a batch
that was unaffected by the problem.  It seems that this was not the case :-(

I unsoldered the eight other similar capacitors (four one each board) from
the H7822 yesterday evening.  I found a small amount of leakage under most
of them but it was was only evident after they were removed from the board.
In general, there was less damage visible under the ones on the lower board
with leads facing down oddly enough.  I thought one of the capacitors from
the upper board had not leaked at all but I left them standing on the bench
overnight with their leads upwards and they all have some signs of leakage
visible on them today.

The capacitor from the upper board that leaked enough for me to notice it
might be under greater stress when operating than the others.  I think the
same capacitor in the H7821 power supplies seems to leak more in those too.
Maybe it carries greater ripple current than the others or something like
that?  I can see that the other four similar capacitors make up PI filters
for the +5V and +12V outputs along with a pair of smoothing chokes, however
I can't quite figure out what the more leaky one is responsible for.  It
could be associated with the -12V output which might also be the supply
for the fans.  This part of the circuit is very hard to trace.

I don't have enough spare capacitors to replace the four on the lower
board.  I am going to leave those out, leave the input lead to that board
unplugged and plug the green LED into the upper board.  I hope it will then
behave just like a H7821.  There won't be any power to the front disk drive
connector but I am not using that so it doesn't matter unless the "power good"
output is affected, in which case I will have to think of something else.

I am hoping that the leaky capacitors were responsible for the odd
intermittent failures I experienced with this power supply recently.

Regards,
Peter Coghlan.

>  Maciej

Re: DEC H7822 power supply

[Peter Coghlan via cctalk]

"Maciej W. Rozycki" wrote:
>On Mon, 2 May 2022, Peter Coghlan via cctalk wrote:
>
>> Thankfully, it doesn't seem to have been there long and didn't get a chance
>> to spread around the board.  Bizarrely this capacitor has it's legs pointing
>> upwards and managed to leak while there are similar capacitors on the other
>> board with their legs pointing downwards which don't seem to have leaked 
>> (yet?).
>
> Would the system have been possibly stored upside down sometime?
>

I don't think so.  It may have spent some time lying on it's side due to
deteriorating rubber feet and for ease of access and but I can't see any
reason for it ever being upside down.  Once I discovered this issue a few
years ago, I checked all my power supplies, removed any leaking capacitors
and changed to storing the machines the right way up in a vertical stack,
with newspapers between them in place of the rubber feet.  I hoped this would
prevent any capacitors which hadn't shown any signs of leaking from starting
to leak.  (Now whichever machine I want to work on always seems to be at the
bottom of the stack...)

>
>  These nasty caps do leak even while in storage (and even if never used, 
> not even soldered ever, according to one source, a repair professional).
>

They are nasty and devious.  In my case, the ones that have been stored in
any orientation but not used much seem to have fared better.  I only started
using this machine with the H7822 for extended periods for the first time a
few months ago.  One of the reasons I started using it more is because I
thought it was immune to the leaky capacitor problem!  It never saw any
serious use before that, even when it was new.

I have at least two machines with H7822 power supplies.  Even though they
have capacitors that look the same as the ones in the H7821, the ones in
the H7822 power supplies didn't seem to be showing any signs of leaking
when I examined them some time ago so I thought they might be from a batch
that was unaffected by the problem.  It seems that this was not true :-(

I unsoldered the other eight similar capacitors (four one each board) from
the H7822 yesterday evening.  I found a small amount of leakage under most
of them but it was was only evident after they were removed from the board.
In general, there was less damage visible under the ones on the lower board
with leads facing down oddly enough.  I thought one of the capacitors from
the upper board had not leaked at all.  I left the removed capacitors
standing on the bench overnight with their leads upwards and they all have
some signs of leakage visible on them today.  It's hard to draw any
conclusions.

The capacitor from the upper board that leaked enough for me to notice it
might be under greater stress when operating than the others.  I think the
same capacitor in the H7821 power supplies seems to leak more in those too.
Maybe it carries greater ripple current than the others or something like
that?  I can see that the other four similar capacitors make up PI filters
for the +5V and +12V outputs along with a pair of smoothing chokes, however
I can't quite figure out what the more leaky one is responsible for.  It
could be associated with the -12V output which might also be the supply
for the fans.  This part of the circuit is very hard to trace.

I don't have enough spare capacitors to replace the four on the lower
board.  I am going to leave those out, leave the input lead to that board
unplugged and plug the green LED into the upper board.  I hope it will then
behave just like a H7821.  There won't be any power to the front disk drive
connector but I am not using that so it doesn't matter unless the "power good"
output is affected, in which case I will have to think of something else.

I am hoping that the leaky capacitors were responsible for the odd
intermittent failures I experienced with this power supply recently.

Regards,
Peter Coghlan.

>  Maciej