[cctalk] Re: Xerox 820II U07 Power Supply magic smoke....

[D. Resor via cctalk]

Best I can tell the diodes are Passivated Silicon, Bead diodes, of which there 
are three flavors.
 
https://pdf1.alldatasheet.com/datasheet-pdf/view/1073401/NJSEMI/A15A.html

On EEVBlog it was suggested that these were Sintered Glass Bead diodes.
 
I do believe they are still in okay working condition.  My thought process is 
that they are probably quite noisy.  Installing a modern type of diode would 
also I believe dramatically reduce generation of heat.
 
It is nice that a Power Supply board is laid out in a way that you can access 
all of the components.  Nothing like some of the small 5v switching supplies in 
which most of the components are shoved close together.
 
I downloaded the 1977 GE Semiconductor manual, but it’s not easy to find it 
without a part number.
 
Back when I was in my early 20’s a neighbor whom was an Engineer at Xerox in 
the power supply division at 701 South Aviation Blvd. El Segundo, gave me a 
bundle of those soft bound Motorola reference manuals, some RCA TTL manuals, 
Zener Diode reference etc.  The books sat on my shelf for many years until I 
ran out of room.  I moved them to my shed which at the time was safe from the 
weather.  After years of storage many of them were damaged from dampness etc.  
 
In the last 10 years I realized I should have taken better care of them.  I 
realize they are almost worth their weight in gold.  
 
I was able to find a few of those books used and purchased them at (luckily) 
reasonable prices.
 
I regret that and a home brew vacuum tube combo preamplifier/amplifier stereo 
unit. I was forced to part with.  My father referred to it as “junk taking up 
space”.
 
It contained 4 6V6GTs, 2 12AU7As, and a 5U4 Rectifier.  The front end was early 
GE (germanium I suppose) transistors.  They were of the metal oval shaped black 
painted metal can type with the pinched evacuation nipples.  
 
Don Resor
 
 
 
From: Joshua Rice  
Sent: Thursday, October 13, 2022 9:44 AM
To: D. Resor 
Subject: Re: [cctalk] Re: Xerox 820II U07 Power Supply magic smoke
 
 



On Oct 13, 2022, at 2:32 PM, D. Resor mailto:organlis...@sonic.net> > wrote:

A couple reasons I'd like to have a circuit diagram is to know what the RIFA 
capacitors purpose are.   The other is, a couple of the electrolytic capacitor 
are double covered with what appears to be rubbery heat shrink tubing, 
therefore I cannot read what their value are.  
 
Generally, though not always, these are simply “coupling” capacitors, that are 
used to limit RF interference from appearing on the mains supply. Most, though 
not all, PSUs will work fine without them. Some others won’t function right as 
they’re used for generating clock signals from the mains supply. I believe that 
some PDP-11 supplies use them for this purpose.
 
One of these two electrolytic capacitor appears to have a dried substance 
around the top.  The over-pressure venting cuts in the top of these two 
capacitors are not split.  At this point I cannot tell if it is dried 
electrolyte, cement to hold the sleeve on, or possibly paper.
 
Sometimes it’s just glue , but better safe than sorry, Cut off the sleeving 
(it’s used for electrically isolating the cap from other components), get the 
rating off of it, and replace with like. Probably worth heatshrinking them 
again as well.



Seems someone was in hurry on the day this PS was tested.  I cannot make out 
date, is it 1983?

 <https://www.dropbox.com/s/zlt2ocpqulil13j/pssticker.jpg?dl=0> 
https://www.dropbox.com/s/zlt2ocpqulil13j/pssticker.jpg?dl=0 
 
Looks like ‘85



What type are the diodes, their rating etc.?  I seem to remember this type with 
a black band were rated at 3 amps, but that's all I remember.

The TO-3 transistor/regulator has no P/N silkscreened on it.

Having a circuit diagram helps to cover many bases.  Apparently it's an Astec 
AA12070.
 
It’s unlikely that these would have failed. If they have, i would (as another 
person suggested,) just replace the unit with a modern Meanwell supply. At that 
point, it’s probably not worth the time and effort to replace all the parts. 



Placed the PS board back in the garage to continue airing out! 
 
Don’t fear the RIFA, but keep the windows open, just in case.
 
Josh.
 

[cctalk] Re: Xerox 820II U07 Power Supply magic smoke....

[Chris Zach via cctalk]

Side thought: I had one of those blow up on a BA23 chassis a few months 
ago. When I opened the supply it was full of aluminum paper from the 
inside of the cap; glad it didn't short out any other components.


Remove and replace.

C


On 10/13/2022 11:01 AM, Jon Elson via cctalk wrote:

On 10/13/22 08:32, D. Resor via cctalk wrote:
I do understand that these are common film capacitor types.  There is 
one more smaller .10ufa RIFA branded capacitor hiding near the center 
of the PWB.


A couple reasons I'd like to have a circuit diagram is to know what 
the RIFA capacitors purpose are.   The other is, a couple of the 
electrolytic capacitor are double covered with what appears to be 
rubbery heat shrink tubing, therefore I cannot read what their value are.


Cut the heat shrink with an X-acto knife and peel it off. it should 
leave the marking of the cap intact.  if there are 2 layers, it may be 
the inner layer is the original factory marked wrapper for the cap.  So, 
you might try to not cut through the inner layer.  But,, maybe don't be 
too worried, as the caps definitely sound bad.


Jon

[cctalk] Re: Xerox 820II U07 Power Supply magic smoke....

[Jon Elson via cctalk]

On 10/13/22 08:32, D. Resor via cctalk wrote:

I do understand that these are common film capacitor types.  There is one more 
smaller .10ufa RIFA branded capacitor hiding near the center of the PWB.

A couple reasons I'd like to have a circuit diagram is to know what the RIFA 
capacitors purpose are.   The other is, a couple of the electrolytic capacitor 
are double covered with what appears to be rubbery heat shrink tubing, 
therefore I cannot read what their value are.


Cut the heat shrink with an X-acto knife and peel it off.  
it should leave the marking of the cap intact.  if there are 
2 layers, it may be the inner layer is the original factory 
marked wrapper for the cap.  So, you might try to not cut 
through the inner layer.  But,, maybe don't be too worried, 
as the caps definitely sound bad.


Jon

[cctalk] Re: Xerox 820II U07 Power Supply magic smoke....

[Jonathan Chapman via cctalk]

If the PSU requires too much hacking, you may just want to replace with a 
modern Mean-Well switcher or two. The Aztec supplies used in those Xerox 
enclosures are OK but nothing stellar. I recapped mine (it also showed signs of 
electrolytic leakage) and it did work so I kept it, but if it'd had issues I'd 
have junked it.

Thanks,
Jonathan




--- Original Message ---
On Thursday, October 13th, 2022 at 09:32, D. Resor via cctalk 
 wrote:


> 
> 
> I do understand that these are common film capacitor types. There is one more 
> smaller .10ufa RIFA branded capacitor hiding near the center of the PWB.
> 
> A couple reasons I'd like to have a circuit diagram is to know what the RIFA 
> capacitors purpose are. The other is, a couple of the electrolytic capacitor 
> are double covered with what appears to be rubbery heat shrink tubing, 
> therefore I cannot read what their value are.
> 
> One of these two electrolytic capacitor appears to have a dried substance 
> around the top. The over-pressure venting cuts in the top of these two 
> capacitors are not split. At this point I cannot tell if it is dried 
> electrolyte, cement to hold the sleeve on, or possibly paper.
> 
> Looking at these two again, it definitely could be dried electrolyte. I have 
> seen it creep out and up into strange places.
> 
> https://www.dropbox.com/s/18hzfdqe96vmgsr/electrolytics.jpg?dl=0
> 
> Seems someone was in hurry on the day this PS was tested. I cannot make out 
> date, is it 1983?
> 
> https://www.dropbox.com/s/zlt2ocpqulil13j/pssticker.jpg?dl=0
> 
> What type are the diodes, their rating etc.? I seem to remember this type 
> with a black band were rated at 3 amps, but that's all I remember.
> 
> The TO-3 transistor/regulator has no P/N silkscreened on it.
> 
> Having a circuit diagram helps to cover many bases. Apparently it's an Astec 
> AA12070.
> 
> Placed the PS board back in the garage to continue airing out! 
> 
> Don Resor
> 
> 
> 
> 
> 
> -Original Message-
> From: Joshua Rice via cctalk cctalk@classiccmp.org
> 
> Sent: Thursday, October 13, 2022 4:43 AM
> To: General Discussion: On-Topic and Off-Topic Posts cctalk@classiccmp.org
> 
> Cc: Joshua Rice ric...@btinternet.com
> 
> Subject: [cctalk] Re: Xerox 820II U07 Power Supply magic smoke
> 
> 
> You shouldn't need a schematic. These thin film caps are a common failure 
> mode on a multitude of PSUs. Just replace like for like. Thin film X and X2 
> rated caps are easily found from your favorite electronics part retailer.
> 
> If it's gold and got RIFA on it, replace it, though. Just because it hasn't 
> popped, doesn't mean it wont pop in the near future.
> 
> I've learned now, to always check every PSU or other mains-powered vintage 
> equipment for these little stinkbombs. If they're present, i'll always 
> replace.
> 
> Cheers, Josh
> 
> -- Original Message --
> From: "D. Resor via cctalk" cctalk@classiccmp.org
> 
> To: "Classic Computer Mailing List" cctalk@classiccmp.org
> 
> Cc: "D. Resor" organlis...@sonic.net
> 
> Sent: Thursday, 13 Oct, 2022 At 12:24
> Subject: [cctalk] Xerox 820II U07 Power Supply magic smoke
> Where might I find a schematic diagram for the Xerox U07 8" FDD,HDD expansion 
> cabinet for the 820II, and/or the 105P80450 power supply?
> The Xerox Professional Computer Technical Reference Manual I downloaded from 
> bitsavers.org doesn't seem to have those particular schematic diagrams.
> For your enjoyment the part which smoked.
> https://www.dropbox.com/s/al9kx3yw9ypwp89/Xerox105p80450.jpg?dl=0
> https://www.dropbox.com/s/al9kx3yw9ypwp89/Xerox105p80450.jpg?dl=0
> 
> I certainly am glad I have the lid off while testing. Unfortunately these 
> capacitors which appear to be film type were hidden from view.
> The fuse didn't blow, but that .22uf 250v capacitor certainly stunk up the 
> house. It smelled like burnt popcorn, plastic and the bottom of a coffee pot 
> which has boiled dry, yech!
> I know that if I had pulled the power supply board first I might have seen 
> the physical cracks in these boxed capacitors.
> Wasn't it Marc V. that said in one of his videos, you don't need to shotgun 
> them all! Oi, lol It's when things like this happen that I most always worry 
> about not going over vintage equipment fine tooth comb.
> Don Resor
> 
> 
>

[cctalk] Re: Xerox 820II U07 Power Supply magic smoke....

[D. Resor via cctalk]

I do understand that these are common film capacitor types.  There is one more 
smaller .10ufa RIFA branded capacitor hiding near the center of the PWB.  

A couple reasons I'd like to have a circuit diagram is to know what the RIFA 
capacitors purpose are.   The other is, a couple of the electrolytic capacitor 
are double covered with what appears to be rubbery heat shrink tubing, 
therefore I cannot read what their value are.  

One of these two electrolytic capacitor appears to have a dried substance 
around the top.  The over-pressure venting cuts in the top of these two 
capacitors are not split.  At this point I cannot tell if it is dried 
electrolyte, cement to hold the sleeve on, or possibly paper.

Looking at these two again, it definitely could be dried electrolyte.  I have 
seen it creep out and up into strange places.

https://www.dropbox.com/s/18hzfdqe96vmgsr/electrolytics.jpg?dl=0

Seems someone was in hurry on the day this PS was tested.  I cannot make out 
date, is it 1983?

https://www.dropbox.com/s/zlt2ocpqulil13j/pssticker.jpg?dl=0 

What type are the diodes, their rating etc.?  I seem to remember this type with 
a black band were rated at 3 amps, but that's all I remember.

The TO-3 transistor/regulator has no P/N silkscreened on it.

Having a circuit diagram helps to cover many bases.  Apparently it's an Astec 
AA12070.

Placed the PS board back in the garage to continue airing out! 

Don Resor





-Original Message-
From: Joshua Rice via cctalk  
Sent: Thursday, October 13, 2022 4:43 AM
To: General Discussion: On-Topic and Off-Topic Posts 
Cc: Joshua Rice 
Subject: [cctalk] Re: Xerox 820II U07 Power Supply magic smoke


You shouldn't need a schematic. These thin film caps are a common failure mode 
on a multitude of PSUs. Just replace like for like. Thin film X and X2 rated 
caps are easily found from your favorite electronics part retailer.

If it's gold and got RIFA on it, replace it, though. Just because it hasn't 
popped, doesn't mean it wont pop in the near future.

I've learned now, to always check every PSU or other mains-powered vintage 
equipment for these little stinkbombs. If they're present, i'll always replace.

Cheers, Josh

-- Original Message --
From: "D. Resor via cctalk" 
To: "Classic Computer Mailing List" 
Cc: "D. Resor" 
Sent: Thursday, 13 Oct, 2022 At 12:24
Subject: [cctalk] Xerox 820II U07 Power Supply magic smoke
Where might I find a schematic diagram for the Xerox U07 8" FDD,HDD expansion 
cabinet for the 820II, and/or the 105P80450 power supply?
The Xerox Professional Computer Technical Reference Manual I downloaded from 
bitsavers.org doesn't seem to have those particular schematic diagrams.
For your enjoyment the part which smoked.
https://www.dropbox.com/s/al9kx3yw9ypwp89/Xerox105p80450.jpg?dl=0
<https://www.dropbox.com/s/al9kx3yw9ypwp89/Xerox105p80450.jpg?dl=0>
I certainly am glad I have the lid off while testing.  Unfortunately these 
capacitors which appear to be film type were hidden from view.
The fuse didn't blow, but that .22uf 250v capacitor certainly stunk up the 
house.  It smelled like burnt popcorn, plastic and the bottom of a coffee pot 
which has boiled dry, yech!
I know that if I had pulled the power supply board first I might have seen the 
physical cracks in these boxed capacitors.
Wasn't it Marc V. that said in one of his videos, you don't need to shotgun 
them all! Oi, lol It's when things like this happen that I most always worry 
about not going over vintage equipment fine tooth comb.
Don Resor

[cctalk] Re: Xerox 820II U07 Power Supply magic smoke....

[Jonathan Chapman via cctalk]

> If it's gold and got RIFA on it, replace it, though.

- snip -

> I've learned now, to always check every PSU or other mains-powered
> vintage equipment for these little stinkbombs. If they're present, i'll
> always replace.

Yup, always replace. These are not parts that can be rehabilitated. RIFAs are 
one of the few things we always bulk replace without any sort of testing.

Thanks,
Jonathan

[cctalk] Re: Xerox 820II U07 Power Supply magic smoke....

[Joshua Rice via cctalk]

You shouldn't need a schematic. These thin film caps are a common 
failure mode on a multitude of PSUs. Just replace like for like. Thin 
film X and X2 rated caps are easily found from your favorite electronics 
part retailer.


If it's gold and got RIFA on it, replace it, though. Just because it 
hasn't popped, doesn't mean it wont pop in the near future.


I've learned now, to always check every PSU or other mains-powered 
vintage equipment for these little stinkbombs. If they're present, i'll 
always replace.


Cheers, Josh

-- Original Message --
From: "D. Resor via cctalk" 
To: "Classic Computer Mailing List" 
Cc: "D. Resor" 
Sent: Thursday, 13 Oct, 2022 At 12:24
Subject: [cctalk] Xerox 820II U07 Power Supply magic smoke
Where might I find a schematic diagram for the Xerox U07 8" FDD,HDD
expansion cabinet for the 820II, and/or the 105P80450 power supply?
The Xerox Professional Computer Technical Reference Manual I downloaded 
from

bitsavers.org doesn't seem to have those particular schematic diagrams.
For your enjoyment the part which smoked.
https://www.dropbox.com/s/al9kx3yw9ypwp89/Xerox105p80450.jpg?dl=0 

I certainly am glad I have the lid off while testing.  Unfortunately 
these

capacitors which appear to be film type were hidden from view.
The fuse didn't blow, but that .22uf 250v capacitor certainly stunk up 
the
house.  It smelled like burnt popcorn, plastic and the bottom of a 
coffee

pot which has boiled dry, yech!
I know that if I had pulled the power supply board first I might have 
seen

the physical cracks in these boxed capacitors.
Wasn't it Marc V. that said in one of his videos, you don't need to 
shotgun

them all! Oi, lol
It's when things like this happen that I most always worry about not 
going

over vintage equipment fine tooth comb.
Don Resor