I have an iMac G5 ALS 20" AcBel PSU I'm trying to repair. When I first got this computer it would run for a while and then shut down without warning. The computer's motherboard caps looked good and I tried the PSU in a different computer and it did the same thing. So I opened up the PSU and found one bad cap. I went and changed all the cold side caps, but when I put it back it would not power up at all. So I opened up the PSU again and changed out transistor Q1, it tested bad. I put the PSU back in the computer and it started right up. I went to shut it down and when I did LED #2 on the motherboard dimmed but did not go out on shutdown, like the PSU did not turn off completely. Weird I thought. I unplugged it and the replugged it in. This time when I went to restart it I got LED #1 but that's it. It would not start. So I put the PSU back on the bench. I jumped pins 15 and 16, but I only could read standby power, i.e. ~6 volts on pin 9 and ~25 volts on pin 22. I thought maybe ic3845 was bad, so I changed it out but it didn't help. I change a few other P1 transistors, but nothing. OK Has anyone else seen something like this, and might know what to try next? Thanks in advance.
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Re: iMac G5 20" Acbel PSU Looking for ideas
What caps did you change? What brand/series did you use? Double check all caps polarity.
You did make a cap map, correct?
What is the API # of the PSU board? The Apple P/N is essentially useless, but it would be nice to put that in here also. They use(d) the same model number with different boards
Shotgunning these supplies is the wrong approach. i.e. - replacing all the parts with the hope you'll eventually get the right one
Toastveritas odium parit
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