Hey experts, I have here a System 1 power supply that I'd like to rebuild just for fun. The previous owner had replaced it with an aftermarket in an attempt to get the machine working. The machine is now working great with the new power supply but I wanted to fiddle with this one to see if I could get it going again.

Before I looked anything up online I hastily reassembled it and plugged it in just to see where it was at. The previous owner had it disassembled in pieces when I got it. I didn't realize that I was missing the insulators, so it went poof! Oops

So after actually reading a couple guides on these I replaced Q1, Q2, and LIC1 for obvious starters (with insulators!), CR3 and CR4 because they burned, and all the electrolytic caps. Now my low voltages (5, -12, 8, 4) are 5.58V, -11.92V, 8.72V, and 4.16V so the low voltage side seems pretty good. Are the 8 and 4 reference voltages close enough? Couldn't find how accurate those should be. I realize I can trim the 5V.

Now for the high voltage side, I was getting like 90V I think where 60V should be. I noticed R14 and R17 were pretty hot and looked cooked so those should be replaced obviously. For the cost of shipping it was cheap enough to simply order EVERY component for the high voltage side. I started with the bridge rectifier diodes but thought maybe I should stop to learn something here. So my question-

Is there a way to go about this systematically to find out where the issue lies or will I just cause more damage replacing some components and leaving others that are possibly bad?

My thought as an amateur was to replace Q3, Q4, and the burned resistors and see where I was at, but I'm afraid if something else is goofed I'll just smoke the new transistors.

Obviously I have a rudimentary knowledge of electronics especially passive components and am a skilled solderer of mostly analog stuff but when it comes to theory of transistor pairs and whatnot I start to get lost.

Thanks!

Cool, thanks for the advice. Yeah I ordered three of literally everything for the high voltage side for $13 shipped. I started a full rebuild but thought maybe I should try to only repair what was needed. It'll be easy to just replace everything though. I didn't have half watt resistors on hand so I ordered them as metal film, sounds like those will still be better than the original but metal oxide would've had the best properties for this application?

After the rectifier diodes I pulled C7 as it's been mentioned as a failure point as well as Q3 and Q4 before posting. Of those Q4 seems dead.

So let's say I didn't have all components handy or they were expensive. Would it be wise to replace the cooked resistors and Q4 then bench test?

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OK, I'm close now.

I replaced Q3 and Q4 (Q2 already replaced), zeners CR10, CR11, and CR12, R14 and R17.

Voltages are all good now except that I had to trim R16 almost all the way to get 60V. Then it slowly decreases. After about 5 minutes I had R16 maxed and 60V had fallen to about 55V. What would cause this?

I got 95V across C6 so it's in the circuit somewhere. C9 and C10 weren't replaced because I accidentally ordered 0.1mfd instead of 1mfd but I removed both and tested extremely close to 1mfd. Could it be a funky resistor failing with heat? I left most of them in because they checked fine with the transistors and zeners removed.

Okay now everything on the high side has been replaced except for the two tantalum caps and I'm still losing voltage slowly. Played 3 games and was down to 56V.

Any idears?

So if anyone ever has this issue and manages to find this thread, replacing the tantalum caps solved the dropping voltage issue. I realized the two caps I didn't replace were both related the trimmer circuit and I could just replace them with aluminum electrolytic caps I had from a radio shack grab bag. So now I have a solid 60v with the trimmer pot in the middle. Huzzah!

That's what I read, partly why I put them back in place originally. I just tested them again and neither are shorted and both show 1mfd on my DMM.

There's no reason I need tantalums there, right? They must've used them originally to save space?