RetroChallenge 2021/10 Entry: PowerMac G4 repair

Hi Everyone,
My entry for RetroChallenge 2021/10 is this PowerMac G4 that powers on, but no video.

I have already taken it apart this morning. Found some leaky capacitors. Photos to follow.

Google Photos


That’s great - would love to hear how you get on.

Worked out capacitors that went bad.
C193 22uF 35v
C940 330uF 16v
C937 100uF 6v
C3568 220uF 35v
C3570 220uF 35v
C3308 100uF 6v
C3307 100uF 6v
Google Photos
Google Photos
Google Photos
Google Photos


Bad looking caps swapped out. Reassembled everything. No change. Still chimes, and still no video. Next I will check voltages on the power supply (should have looked at that first).


Here’s the details of the WOzFests I’m holding - feel free to join via Google Meet.

And I might even be able to have 10 attendees at WOzFest 22!

hey Jon,
I’ve done similar repairs to a Mac Classic II. Those aluminium caps are the pits. Like you I had a lot of corroding stuff near to the caps that leaked. Luckily for me my Mac was still working when I last did this about 20 years ago. I think I lost sound on one of the Classic Macs I did and that was due to tracks being eaten by corrosion.
I was thinking of using SMD tantalum caps next time I do one of these repairs as they don’t die and eat the PCB tracks, although they might explode instead :slight_smile: However the Apple //e uses axial tantalums and I’ve only ever had one of those fail in 37 years so it’s not such a stupid idea.
good luck,
Mark C

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Spent the last few hours checking power lines. Here’s what I found: Power supply voltage lines are OK. Then I noticed that the mouse doesn’t “light up” (plugged into keyboard acting as hub).

On a known-good machine, the mouse lights up immediately after powering on. I suspected a fault in the USB 5v line (or some other voltages).

Took logic board out again. A previously repaired capacitor has fallen off. I have re-soldered this one. And nothing else stands out. Upon reassembly, plugged mouse directly into USB port, and it lights up on boot. Apparently it isn’t initialising the hub and/or keyboard as the mouse does not light up when plugged via the keyboard. So there is USB power, but not being initialised… hmm, the plot thickens.

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