Best I can tell the diodes are Passivated Silicon, Bead diodes, of which there are three
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
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
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.
From: Joshua Rice <Rice43(a)btinternet.com>
Sent: Thursday, October 13, 2022 9:44 AM
To: D. Resor <organlists1(a)sonic.net>
Subject: Re: [cctalk] Re: Xerox 820II U07 Power Supply magic smoke....
On Oct 13, 2022, at 2:32 PM, D. Resor <organlists1(a)sonic.net
<mailto:firstname.lastname@example.org> > 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
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
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
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
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.