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[nateman831]

So I acquired a FW800 1.42 off of eBay that looks very clean - and also included a Radeon 9700 Pro. But I digress...

It was booting just fine. Until I swapped the GPU with a GeForce4 Ti 4600. The machine no longer boots.

I put the original Radeon 9700 Pro back in. Still no dice.

I put the GeForce back in the MDD 1.25 I got it from and that machine still boots just fine.

I tried removing the battery, pressing the CUDA button, reseating the RAM, checked cable connections. Still no dice.

The power button lights up when I press it. And maybe a fan inside half spins for a split second, but no other signs of life.

Is there anything else I need to check? Or are the PSUs on these units THAT bad?

I'm hoping to not have to rebuild the PSU or buy a new one. But perhaps thats part and parcel for buying one of these...

*edit: I just noticed this machine has the 360W AcBel PSU. Meanwhile, my still-working MDD 1.25 has the 400W AcBel... Not exactly what I'd expect, but what do I know...

[IIO]

given that you already did a cuda reset, this sound exactly like a broken PSU.

not sure if it means that bad that something breaks after 20 years, but i´ve seen b&w and quicksilvers die before, and they are said to have better psu´s than mdd´s

[GaryN]

Welcome to the Wonderful World of Magic Mirrors…
I'm pretty sure you're the guy I recently commed with on FB. Your situation sux BUT it could be worse. You at least still have a complete working MDD.

Start here: http://www.jcsenterprises.com/Japamacs_Page/Blog/D275729F-09DA-4FBB-96B3-BEEEB2C04619.html
You use this guide to test the PSU pin-by-pin.
If you don't have a voltmeter, buy one. They're mandatory when using 20+year-old hardware anyway. It doesn't have to expensive.
If you find a PSU issue - and you very likely will - you can get it rebuilt here: https://www.ebay.com/str/baltimora2000?_trksid=p2047675.l2563

This guy has repaired many, many MDD and QS PSU's, is reliable and does good work.

HOWEVER, since it's the holidays, his turnaround time is longer than usual so you can:
1) Send it to him and wait patiently OR
2) Swap in the PSU from your 1.25 THEN Send the bad one to him anyway because your working one is just as old and they all can and do fail without warning.

If the PSU tests good

Did you get a monitor with that FW800? A bad monitor can fry the +25v out on a PSU (OR on the GPU card) and cause a no-start condition.
You can get fooled by that mess if you have say, a DVI monitor on the 1.25 and an ADC monitor on the FW800 because the broken one can sometimes continue to work via DVI.
…… just one of the little perks of Apple's ADC scheme.

Havin' fun now, right?

[IIO]

he also has atx cables? are these the one we know or does he make them?

[nateman831]

@GaryN Thanks! This is very helpful...

We def might have spoken over facebook - I posted the issue in the PowerMac group there...

An update: after leaving the machine unplugged for 24 hrs, pressing the CUDA button, then removing the battery for 5 mins, the machine has now booted again.

It should have a very low load as the only components besides the motherboard are the GPU, disc drive, and an SSD. No PCI cards at the moment, and no other drives. I don't use an ADC monitor or the ADC port - strictly DVI. With a DVI to VGA adapter into my 1080p monitor.

I've gone ahead and purchased an inexpensive (and well-reviewed) multimeter. I'll plan to investigate the PSU in both machines as they are old - thanks for sharing that link.

Does this still sound like a PSU issue now that its booting again? Or is there anywhere else you'd advise looking into?  Not sure whether I'll try swapping GPUs again...

But, most likely, in time, I WILL be swapping the 1.42 chips into the MDD. That machine is booting fine with the GeForce4 Ti 4600, and has the larger 400W AcBel PSU... It will be my OS 9 rig...

I stumbled across the guy who fixes PSUs - its good to hear that his work is reputable. I've gone ahead and bookmarked him.

[GaryN]

We def might have spoken over facebook - I posted the issue in the PowerMac group there...

An update: after leaving the machine unplugged for 24 hrs, pressing the CUDA button, then removing the battery for 5 mins, the machine has now booted again.

Does this still sound like a PSU issue now that its booting again?..

Yup. You were the Insignia TV guy…

The fact it's working again may still mean a failing PSU. There's a common symptom where you get just what you were getting - the button lighting up for a sec and all. Usually, you can make it work by simply unplugging the power for 10 seconds or so and it will start on the next try. You then have to do that each time. I once used a switched power strip to make it easy to do for almost 6 months. I advised others to try it and it worked for them as well. A rebuild solves it.

Note I said "may still mean a failing PSU." Checking voltages might not find a bad or missing voltage in this case. I think it has to do with the trickle voltage that supplies the power button on both the computer and on any attached Cinema Display. This is derived from the +25v main monitor supply for reasons probably known only to Steve Jobs and you can't ask him anymore.

Swapping the 1.42's straight across is no trouble at all. It just works. Be certain that you move the good copper pipe heatsink as well, that you use a good (Arctic Silver or equiv.) thermal goo and that you tighten it down medium-firmly and evenly.

Lastly… DO NOT sell, throw away, or otherwise lose possession of your now "extra" MDD. Rebuild the PSU and keep it all for parts.