Weird Power Issue Power Mac G4 MDD

[D-50 Dude]

Howdy! As the title says, I’m having a bizarre power issue with my MDD. I just finished rebuilding the Samsung 360W PSU (line filter cap, all other caps including the daughtercards, both MOSFETs, and the fuse) and the system seemed to be working fine. I successfully got Mac OS 9.2.2 installed as well. Before I get into the issue, here are some other things of note:

- the PRAM battery was replaced with a new one
- the monitor being used with the computer is an Apple M2454 Studio Display 15” ADC (LCD)

Here’s where the issues started happening. I put in a DVD movie to watch while I was doing something else and for seemingly no reason, the screen went blank and the computer powered off. When the screen went blank, the touch sensor for the backlight adjustment on the monitor lit up white (didn’t even realize it had a led behind it til that happened).

Puzzled, I turned the computer back on and it booted back into Mac OS just fine. Awhile later, I decided to test a game on it and all was going fine except for when I went to adjust the keyboard inputs, then the monitor did that weird thing with the indicator lights again, but this time it only made the computer lock up rather than power off (though I could still move the mouse cursor). The next event was when trying to shut down the computer, instead of it fully powering off, it went into sleep mode and when awakened, it froze at the desktop.

So here are my questions.

Though I’m almost positive it’s not the PSU, could I have done something wrong?

Could it be a faulty ADC monitor? (It makes a buzzing noise if you put your ear up to the top)

I’ve already:
- Reset both the PMU and the PRAM
- Tried different RAM modules

I haven’t tried a DVI monitor yet.

The Computer’s Specifications:
- Dual 1.25GHz CPU card
- 512MB RAM
- ATI Radeon 9000 Pro

Much appreciation for taking the time to read this lengthy post!

 

[Byrd]

I'd try another monitor (or unplug your monitor and continue to play a DVD perhaps) along with testing the +28V rail for ADC; the 15" ADC was pretty reliable but the 17" ADC often had issues with the inverter board, perhaps a similar issue with yours.

 

[D-50 Dude]

Thanks for the replay! I got around to testing it with a DVI monitor (not an ideal one since it’s too new) and the system is stable so far at least with DVD playback. Haven’t had a chance to try a game yet, but since the full power off was during DVD playback, I feel this was a good test. I’ll keep you updated on any further findings.

One other thing of note, I may just be imagining it, but with the DVI monitor connected instead, the system chimed a lot faster on startup.

About testing the ADC power output line, how would I go about doing that with a multimeter? Where would be the best place to probe the voltage and what should it be with no load on it?

Thanks!

 

[D-50 Dude]

Thanks for the replay! I got around to testing it with a DVI monitor (not an ideal one since it’s too new) and the system is stable so far at least with DVD playback. Haven’t had a chance to try a game yet, but since the full power off was during DVD playback, I feel this was a good test. I’ll keep you updated on any further findings.

One other thing of note, I may just be imagining it, but with the DVI monitor connected instead, the system chimed a lot faster on startup.

About testing the ADC power output line, how would I go about doing that with a multimeter? Where would be the best place to probe the voltage and what should it be with no load on it?

Thanks!

That was supposed to be “reply” lol.

UPDATE: I tried the game that was having issues, and it worked perfectly with no lock-ups or shut downs on the DVI monitor. So the fault is definitely ADC related. The question of what the culprit is still remains.