Dead G4 MDD

[Unknown_K]

I went to turn on the G4 MDD under my desk to burn a DL-DVD and it was dead (166 FSB DP 1.33ghz).

The machine has been running fine for years (maybe a few times a month), now no sighns of anything. I popped in a good working PS (my spare) and it just makes the door fan jiggle a little, no power, one of the motherboard lights flashes RED for a split second then nothing. What else could it be?

Switched the machine out with a DP 866 (kinda slow) for now, also have a 1.25ghz Single but I like that one for OS9.

Any ideas?

 

[Nathan]

Try testing the PRAM battery if you have a multimeter and see if it's substantially below the nominal 3.6v (less than 3v). If so, replace that and see if it starts.

 

[Unknown_K]

I tried that no difference.

 

[Nathan]

Obviously it's not new, but a spontaneous failure while not in use does seem odd. Have you looked at the capacitors? Do you always keep it stationary? If you've picked it up and moved it since the last time you used it then it might be worth opening it up and reseating the RAM and/or expansion cards. Assuming it could still boot with just one stick of ram you might try testing each stick separately.

There's a thread from quite a while ago here: https://discussions.apple.com/thread/1536467?tstart=0 They don't seem to come up with any answers, but someone suggesting looking at this: https://web.archive.org/web/20100722061358/http://docs.info.apple.com/article.html?artnum=95064  It's talking about a different G4 model but testing the voltage in-situ if possible might yield an answer as to whether your power supply is the problem or not.

A logic board failure probably isn't out of the question, but you may as well explore other avenues first.

Did you actually replace the battery or did it just measure as good? A brand new battery probably wouldn't hurt. You might also try resetting the PMU. https://support.apple.com/en-us/HT1939 Assuming that the PSU isn't dead and the logic board/motherboard isn't shot the power management clearly isn't working...

 

[Hrududu]

Have you got an ADC Cinema display?  I have a funky MDD that will ONLY come on when powered on through the ADC display power button.  I don't know what it is, perhaps drawing that power through the card, but mine will do exactly what yours does if I try and use the front power button or don't use a ADC display.

 

[Nathan]

Have you got an ADC Cinema display?  I have a funky MDD that will ONLY come on when powered on through the ADC display power button.  I don't know what it is, perhaps drawing that power through the card, but mine will do exactly what yours does if I try and use the front power button or don't use a ADC display.

https://discussions.apple.com/thread/6988411?start=0&tstart=0

It's suggested here in the above thread that the front panel board/power button can be an issue and if so that pushing the button in the "right" way can get it to work. They also mention the possibility of using the early imac keyboard with a power button to circumvent it. If using an ADC display's soft power mechanism works then that means the PSU is probably fine and the power button might be the faulty part.

 

[Unknown_K]

Well while looking for a space to store my iMac G4 I stumbled across another MDD PS. I knew I had one dead one and one tested working spare so this 3rd supply was a surprise. Anyway stuck this supply into the dead MDD and it bonged and works (must have been the working spare).

So now I am back to having 3 working MDD machines and now 3 dead MDD PS's. Just came back to my room to type this and get some labels to mark the dead ones as BAD and banish them to the garage for when I an desperate enough for a working MDDS supply that I will contemplate getting one or more of these fixed.

P.S. Anybody here have luck fixing these things?

 

[Nathan]

Glad to hear you found a solution and it was so simple a fix.

I opened PC power supply up once because it wasn't working. I haven't repaired any myself, but they usually contain an assortment of standard components (fuses, resistors, capacitors, inductors, transformers) plus a couple integrated circuits. Unless the IC chips themselves are toast, there are burnt or vaporized board traces or you have obviously damaged inductors/transformers can probably get away with just:

- checking for board damage including bad, damaged solder joints

- examining the wire harnesses/plugs/connector for obvious breaks, melting or short,

- replacing ALL of the capacitors and any resistors that appear burnt

- checking for blown fuses and replacing it if necessary

You would also want a way to test it on a bench disconnected from anything it could damage, probably with some kind of load (they make huge resistors you cna supposedly use for that) and at minimum check that you get the appropriate voltages. I've read that in an ideal world you want to test it under load and use an oscilloscope to verify that it's output stable, correct voltages.

 

[trag]

So now I am back to having 3 working MDD machines and now 3 dead MDD PS's.

P.S. Anybody here have luck fixing these things?

There are a few threads on the badcaps forums regarding fixing the MDD power supplies, along with parts lists.

http://www.badcaps.net/forum/showthread.php?t=8934

http://www.badcaps.net/forum/showthread.php?t=7165

And possibly more, but those came up without much looking.  You're probably in for a little reading to sort out the useful ones, from the "It no workee" threads.

 

[Unknown_K]

One I know blew a fuse so it would be more then leaking caps I assume. The other one I popped open and didn't see a glass fuse (could be a different type), that one could be bad caps because the PS would jiggle the side fan and briefly light up the power button.

Thing is there is so much stuff crammed into those supplies it would be a pain (and probably expensive) to fix. The last PS I bothered to fix was easy, an LC supply that just needed less then a dozen capacitors to fix. I didn't toss them because I know sooner or later replacement supplies will either have cap rot or be super expensive so I will need to tackle the problem sooner or later (unless G4's don't excite me enough anymore).

I wonder how many hundreds of bad caps I have replaced in the last 15 years just on my gear.