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View Full Version : diagnosing a iMac 400MHz no boot up....


Kyle Nerder
Dec 2, 2005, 12:27 PM
Hello,

I just got my hands on a junker iMac 400MHz. It powers up, but no "dong" chime sound and picture. The screen shows no activity. All I see is the power buton light up.

What is the first step into diagnosing this DOA? I just want this machine as a toy.
Thanks peoples!

Eidorian
Dec 2, 2005, 12:36 PM
http://forums.macrumors.com/showthread.php?t=164915

I'm having the same issues but on a PowerMac G3. Sorry for the lack of help. =\

yellow
Dec 2, 2005, 12:39 PM
No chime means it fails the POST (Power On Self Test).

First step, reset all connections and items inside. RAM, HD, Cables, Videocard, ETC. Open up the box and see what powers up when you power on. Light on the mobo? HD spins up? Fans start?

Eidorian
Dec 2, 2005, 12:50 PM
Ok this is going to be funny. I have a TON of Dell 17" LCD's in my office since is the repair room. I have several VGA cables laying around too. I had kept on plugging in a VGA cable that didn't go to the monitor. It powers on now has has video. Now to get a SATA controller card and some drives for my free server. :D

They gave away this machine to me for free. Yay!

Kyle Nerder
Dec 2, 2005, 01:15 PM
Get back to your own thread! haha:p Glad to hear you got your problems solved.

OK, so I checked this unit out.

Ram was plugged in fine. I switched slots. - Still dead - I have more RAM at home I would like to try in it

HD - It doesn't appear to spin up. Maybe it's toast, but you would think it would still fire up the screen and say the HD is NFG.

There are 2 lights that turn on. 1 at the power button and 1 at the ata drive plug on the main board.

Also I do not hear any fans, but I don't think these iMacs have fans.

This is a 350MHz unit. I said 400 earlier and that was a mistake. Slot loading cd.

biohazard6969
Dec 2, 2005, 02:36 PM
i have the EXACT same problem with a 400mhz imac slot loading and havn't gotten any farther with a diagnosis than you

yellow
Dec 2, 2005, 02:46 PM
Have we tried the age old zappage of the PRAM?

aquajet
Dec 2, 2005, 02:50 PM
Sounds like a bad analog board. This is the most common failure in these machines (in my experience), especially the 233-333 mhz iMacs.

Kyle Nerder
Dec 2, 2005, 04:15 PM
Sounds like a bad analog board. This is the most common failure in these machines (in my experience), especially the 233-333 mhz iMacs.
Is that the same as the "PAV" board on the 350MHz. I hear it is a common prob.

aquajet
Dec 2, 2005, 06:27 PM
Is that the same as the "PAV" board on the 350MHz. I hear it is a common prob.

Yes, that's the Power/Analog/Video board.

It's also possible that the PMU chip is corrupted. This could be caused by a dead backup battery. If you've got a multimeter, measure the voltage. It should read 3.3-3.7 volts.

Assuming the battery is good, reset the PMU chip by pressing the reset switch (only once), located at S1 on the logicboard. This is located to the left of the port cluster, and to the right of the memory slots.

Kyle Nerder
Dec 2, 2005, 08:21 PM
Yes, that's the Power/Analog/Video board.

It's also possible that the PMU chip is corrupted. This could be caused by a dead backup battery. If you've got a multimeter, measure the voltage. It should read 3.3-3.7 volts.

Assuming the battery is good, reset the PMU chip by pressing the reset switch (only once), located at S1 on the logicboard. This is located to the left of the port cluster, and to the right of the memory slots.
Ok I went through all that. I even got my hands on a repair PDF and got the volt meter out. Everything looks other then the voltages at J7 Down Converter. I didn't receive any voltage at pins 2,4 and 14. So I am assuming the Power Audio Video Board is NFG. I attempt to replace it as I have seen them on eBay for 20 bones, but the idea of removing the CRT/discharging sounds scary.

Unless there is another solution without sinking money into this junker, I am going to turn this machine into parts for some other iMac G3's I have at the shop.

Thanks for your help everyone.

aquajet
Dec 2, 2005, 08:39 PM
Ok I went through all that. I even got my hands on a repair PDF and got the volt meter out. Everything looks other then the voltages at J7 Down Converter. I didn't receive any voltage at pins 2,4 and 14. So I am assuming the Power Audio Video Board is NFG. I attempt to replace it as I have seen them on eBay for 20 bones, but the idea of removing the CRT/discharging sounds scary.

Unless there is another solution without sinking money into this junker, I am going to turn this machine into parts for some other iMac G3's I have at the shop.

Thanks for your help everyone.

You won't measure any voltage at pins 2, 4 or 14 unless the computer is actually on.

Have you checked the fuse at F901? If it's open, then the analog board is probably toast. Otherwise, it's probably the logic board. At least at that point, you can decide which parts are still good.

Kyle Nerder
Dec 2, 2005, 09:01 PM
You won't measure any voltage at pins 2, 4 or 14 unless the computer is actually on.

Have you checked the fuse at F901? If it's open, then the analog board is probably toast. Otherwise, it's probably the logic board. At least at that point, you can decide which parts are still good.
yeah it was on when I checked them when it was on.
Fuse F901 was good.

These machines aren't much more then paper weights anyways. I just wanted another junker for inter-webbing.

I got a Power Mac G5 not too long ago and I wonder why I spent 3 hours on the thing. LOL