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  1. ahahthunder

    Loud Pop When starting Mac Classic, Performance Unaffected

    Yep, as soon as I read your post I checked those diodes and found DP3 to have failed. Replaced those and now the mac is back in working order! Still undervoltage on cold starts, but as long as it works I'm happy. Thanks for the help!
  2. ahahthunder

    Loud Pop When starting Mac Classic, Performance Unaffected

    I've finished replacing every capacitor on the AB now and it did not seem to improve performance. After a few days of continued function (under-powered on cold starts, otherwise OK) the computer suddenly died. The hard drive, fan, and display show no signs of life. Using a multimeter, I've found that not all capacitors are being charged. The big 220V ones seem OK, but the cluster near the speaker read 0V. I re-soldered that ZP1 transformer since it did seem kind of jank, and I re-soldered RP2. I guess it's time to start looking at diodes & transistors. Although I wonder if these symptoms could narrow down this problem. It's a rev. 2 classic 120V AB board with known good caps. ZP1 did a few arcs like a week before death. It's not blowing fuses. Could a single diode or transistor stop everything like this? I'm a little out of my area of expertise here but when I know everything else works I don't want to quit.
  3. ahahthunder

    Loud Pop When starting Mac Classic, Performance Unaffected

    The burned solder joints in question here are actually original; I didn't do them. There's a gap cut out of the board here to really separate those two points. Maybe they expected something like this was possible in design. Could a condition cause over voltage here enough to arc like that?
  4. ahahthunder

    Loud Pop When starting Mac Classic, Performance Unaffected

    Ok I think I found the problem. The protective paper on the AB has a burn mark and some solder is has soot on it. I'm touching the component where the short happened, but it seems like that paper is just shorting those two points. I'm going to go through with the cap replacement today. Is there something I can do to prevent this?
  5. ahahthunder

    Loud Pop When starting Mac Classic, Performance Unaffected

    I've heard the pop two times. Could a capacitor do that twice? Also, I've never heard of this 'safety capacitor' before; I am new here. Can you give/point me to some more information on this? Does it need replacing?
  6. I'm repairing a classic. I've so far washed and replaced all capacitors on the logic board, and replaced a few on the analog board. The machine almost works fine except cold starts usually have horizontal lines on screen for the first minute or so. I assume this is due to the capacitors I've yet to replace. However, now when I do a cold start, there's a small chance that I hear a very loud pop. I thought it must be a capacitor exploding so I switched it off immediately and later took it apart to inspect the boards. I found no blown capacitors on either analog or logic board. I plugged the computer back in and turned it on again and it started working again just like before, if not a little better. There was no horizontal lines it just started up perfectly. The next day I turned it on and it booted again perfectly. Then I moved it into another room and it made the loud explosion sound again, then proceeded to successfully boot. What is going on here?
  7. ahahthunder

    Macintosh Classic under-voltage

    I got a Macintosh Classic in decent but non-working state. After washing and recapping the logic board it worked great. A few days later I've noticed what seems like the analog board failing. The computer turns on with wavy horizontal lines for a few minutes until the logic board comes on. Then it takes another minute for the hard disk to start spinning. (I've plugged the hard drive into a known working power supply and it spins up right away.) However last time I used the computer, after warming it up and using it for a few hours it crashed into a restart loop. Now it won't ever get to start the logic board. I suspect this is a power supply issue or at least a known, common problem. How do I fix this?