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
