iMac Power LED

Posted by: yann86

iMac Power LED - 01/20/06 07:23 AM

I have recently made a succesful conversion of an iMac DV 400 to make it 600MHZ with 16MB VRAM. Anyway since I have done the conversion, the power light on the front stays orange and is very faint. Also the first time I booted the machine the screen was all f***** up, this has just disappeared and now it works perfecly fine except for the power LED. Any ideas as to what is causing this?

EDIT: Language

Post edited by: yann86, at: 2006/01/20 16:33
Posted by: TCPMeta

Re:iMac Power LED - 01/20/06 07:29 AM

Sounds like you're straining the power supply. You maybe want to look into a ATX power supply mod for that very soon.
Posted by: yann86

Re:iMac Power LED - 01/20/06 07:39 AM

Should I be worried about this? And I don't think an ATX supply would fit in there, would it?
Posted by: maestro

Re:iMac Power LED - 01/20/06 08:22 AM

Not sure whats up with that. Maybe it is a power issue. You are running a high OC. Try backing the speed
down and see if that changes it. By the way, please watch you language, we have many younger readers and
people who are uncomfortable with the F bomb. Thanks.
-maestro
Posted by: yann86

Re:iMac Power LED - 01/20/06 08:34 AM

Sorry about the language. Anyways it's not overclocked, it's an original 600MHZ PPC750cx motherboard.
Posted by: Waragainstsleep

Re:iMac Power LED - 01/20/06 11:03 AM

The 600s had a different power supply to the 400s. The one I tried swapping wouldn't even boot. I would say TCP is spot on with his estimate of straining the PSU.
What you choose to do about it is up to you, but if you don't have the PSU form the 600 or its dead, or you simply don't wish to swap it as they are a pain to swap (Not to mention dangerous) then an ATX conversion would seem to be the easiest fix. If not the most elegant.
Posted by: yann86

Re:iMac Power LED - 01/20/06 01:38 PM

Waragainstsleep wrote:
Quote:
an ATX conversion would seem to be the easiest fix. If not the most elegant.

Do you mean putting the mobo in an ATX case? I'd prefer to keep my iMac the way it is. Plus it works better than ever with the new mobo, so unless there's some kind of danger that me or my mac are in at the moment I don't see the point of another mod.
Posted by: Waragainstsleep

Re:iMac Power LED - 01/20/06 02:34 PM

Its quite simple really. The PSU on the 400MHz is built to run a 400MHz chip and its various ancillaries. A 600MHz chip (if it is the same chip, which it is), will use more power than a 400MHz chip. Like I say when I tried it, it wouldn't even power on, and we have established that your PSU is very likely to be under more strain than it was designed for.

This is not unlike overclocking your PSU. It may well be fine. Or it may not work (as in my case).If it does work it will almost certainly shorten the life of the PSU, and these are the weak point on G3 iMacs anyway.
If the PSU fails, it may do so without event. Or it may melt. Or it may explode. Or catch fire. I'm not trying to worry you, this is unlikely to happen.

But its best to get into good habits. I would do something about the PSU if I were you.
I wonder if you could fit a 1U ATX PSU into the bottom of the iMac case...... That would be quite original. I've never seen it done.
Posted by: yann86

Re:iMac Power LED - 01/20/06 02:52 PM

Waragainstsleep wrote:
Quote:
it may melt. Or it may explode. Or catch fire. I'm not trying to worry you, this is unlikely to happen.

But its best to get into good habits. I would do something about the PSU if I were you.
I wonder if you could fit a 1U ATX PSU into the bottom of the iMac case...... That would be quite original. I've never seen it done.


You really freaked me out on fire/exploding part. And on the 1U ATX PSU, I really doubt that's a possibility as there's little room down there + cooling won't improve. I might just try to get my hands on an authentic 600MHZ iMac PSU.

By the way, the chip is different. The 400MHz one is a normal PPC750, the 600MHZ one is a PPC750cx. Don't know if there's much difference though...

Anyways thanks for the help and I'll kee you posted (if my mac doesn't explode in my face that is:blink: )
Posted by: Waragainstsleep

Re:iMac Power LED - 01/20/06 03:08 PM

Relax, if it was going to explode, it probably would have by now. Just keep an eye on the temperature. If the case is getting too warm, shut it down for a bit. Perhaps avoid leaving it running for long periods or while you're out of the house.

Even if it fails, it will probably just stop running. Don't panic, just show it some respect until you get to trust it. If it stays pretty cool, its probably fine.
Posted by: yann86

Re:iMac Power LED - 01/20/06 03:10 PM

Well, the top half of the casing gets warm and I can feel the warm air rising when I hold my hand over the top grill. It doesn't seem any warmer than before though. By the way, I was planning a cool light mod, do you think I can add another 10 LEDS, as far as I know LEDS use only a tiny bit of power.

EDIT: I was just wondering, what part(s) exactly are we talking about. Is it the little converter board attached to the mobo or the larger beige board in the 'high voltage compartment'?

Post edited by: yann86, at: 2006/01/20 23:22
Posted by: yann86

Re:iMac Power LED - 01/21/06 04:44 AM

Okay, so now the problem I mentioned in my first post seems to be back. The screen was blurry on first boot, then fine for about 6-7 hours and now it just stays blurred. I don't know for sure if it's the PSU, I've been checking part numbers and I'm absolutely sure the 'power down board' is the same on all iMac G3s, also the 'video analog board' (the larger beige one in the crt area) seems to be the same for all revisions. Could it be the CRT itself that's different in later iMacs (needing less power) or something else?

I've been thinking about replacing the CRT with an LCD as seen in the eye-mac mod on this site.
Posted by: yann86

Re:iMac Power LED - 01/21/06 06:32 AM

I've just tried connecting an LCD monitor to the built-in VGA, the screen was as blurry as the internal CRT. Can this be explained by the PSU overload theory? The LCD has its own power supply of course.
I'd really want to make sure this isn't a problem with the mobo.
Posted by: soward

Re:iMac Power LED - 01/21/06 07:30 AM

I would suspect heat before power anomalies. Any way you can run it opened up with some temporary extra cooling?
It could also be a bad connection somewhere, I haven't had an iMac open in a long, long time, so I don't recall and most likely points to check, but...
Posted by: yann86

Re:iMac Power LED - 01/21/06 07:45 AM

soward wrote:
Quote:
I would suspect heat before power anomalies. Any way you can run it opened up with some temporary extra cooling?

I would suspect so too if the problem occured a few minutes after booting, but the screen goes blurry right away.

Anyway I seem to have found some more information. The power down board is the same for all models but the video analog board has 3 versions.
661-2212 rev. A and B for 350, 400Mhz models
661-2465 for 450 and up.
There are only minor differences, so I feel kinda screwed over by apple at the moment :angry:

Replacing the video analog board doesn't seem an option as that would cost me quite a bit. So again, this leaves me stranded with the monitor replacement option. This would cost a lot aswell, I know but the difference is I actually get something out of this mod (a shiny LCD monitor).
Posted by: Waragainstsleep

Re:iMac Power LED - 01/21/06 09:25 AM

An LCD would need a whole lot less power....
Posted by: yann86

Re:iMac Power LED - 01/21/06 10:00 AM

Waragainstsleep wrote:
Quote:
An LCD would need a whole lot less power....

That's the whole point of the mod;)