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macosten

Quadra 950 PSU pains

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So, I recently got a Quadra 950 and had it shipped to me. Naturally, it was working, but shipping happened, and it's acting up a bit now.

 

I've surmised that it has a problem similar to that described in this post. If I let it sit, then try turning it on with soft power immediately after plugging it in, then I can either get it to turn on and boot normally, or I can get it to turn on and then off again right after that. In fact, the symptoms in the third post of that topic are basically identical to those in my machine. The main difference is that I have a very hard time actually getting it to get to that full boot and can't do it reliably - more often than not, I'll hear the speaker come on, and then the power will cut out again.

 

It's nice knowing that my other components work, since I did get it to boot once or twice, but I'd like it a lot if I could get it to boot consistently (and if I want to put more cards and/or drives into it, I'm going to want a reliable PSU anyway). I imagine it involves a recap of some sort, or I could alternatively replace it with an ATX PSU using Geekdot's method, or some variation of it. Whatever works, honestly.

 

What do you suggest? If it's a matter of replacing a few caps, which caps need replacing, and what values are they?

 

Finally, as a list of things I did that didn't change much, and observations about the machine I was able to make while it was booted up:

I cannibalized my CC's known-working PRAM battery, but that didn't fix it (it may have helped, but I can't tell).

I have given the machine a good dusting-off, but I have not reseated absolutely everything (I did reseat some of the VRAM, though, since it came with the full four sticks).

Minimizing the number of cables going towards the board didn't change anything.

The front-facing buttons are not stuck or shorted; they work properly.

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The 950 motherboard doesn't have any leaking type capacitors.

 

I would strip the unit of any cards cables and drives and see if it reliably boots to the cursor looking for a bootable partition. If not then take the motherboard out and look it over for cracks, broken bits, screws stuck under it, etc. Check the power cables for bent pins or something out of place. Make sure the RAM is installed in exact sets of 4 with two on the top bank and 2 on the bottom.  Limit the RAM to just 4 sticks to start. Re assemble and try it again.

 

Those power supplies are built like a tank and they would be the last thing I would think of replacing.

 

 

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Ive came across to a few Q900/950 - those PSU does fail as it'll need to replace the caps. I have one sitting there waiting to be recapped in the PSU.

Logicboard does not have any sort of leaky caps.

Cheers

AP

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16 hours ago, Unknown_K said:

I would strip the unit of any cards cables and drives and see if it reliably boots to the cursor looking for a bootable partition. If not then take the motherboard out and look it over for cracks, broken bits, screws stuck under it, etc. Check the power cables for bent pins or something out of place. Make sure the RAM is installed in exact sets of 4 with two on the top bank and 2 on the bottom. Limit the RAM to just 4 sticks to start. Re assemble and try it again.

 

Those power supplies are built like a tank and they would be the last thing I would think of replacing.

Just tried this again, just to be sure; I checked to make sure nothing conductive was under the board, made sure all the pins were normal, I removed all the RAM and replaced it with one bank of brand-new modules in Bank A, I removed the NuBus card it came with, tried with and without the VRAM, nothing connected to the PSU except the logic board, and...

 

Nothing. Not even a speaker pop, and no fan movement.

 

I couldn't see anything broken or burned out on the board. I did clean a discolored area near the 

 

I've got a multimeter set to measure VDC and even as I'm sticking the red end into the blue pin and the black end into a ground pin, even as it's plugged in, I'm getting literal zero from the blue pin to ground. I think that might be a problem (unless I'm really messing up how to use a mutlimeter...).

 

I think I'm about 98% sure that the PSU is to blame somehow.

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Many years go I had a dead Q950 and ended up going to Cleveland to snag one free (ended up with a trunk of goodies). Anyway I swapped the good supply into the dead unit and it worked, I put the dead supply into the new unit and it also worked. What the problem was I have no clue. I just chalked it up to a pin in the PS cable not making contact and went about my business.

 

 

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Loose connection talk has me thinking, especially given the fact that it was shipped. Are the key leads securely connected to the logic board? You’d need the top sled out to check properly.

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Alright, so what I've ended up doing is rewiring a PC power supply to match the Quadra's power. At first, I wasn't getting it to work... but it turns out that was because the brand-new RAM I ordered was messing it up. When it was in Bank 1, the machine didn't chime, and when it was in Bank 4, it chimed, and then gave me the Chimes of Death right after. Without that bad new RAM, though, it works normally.

 

My setup is a bit ugly (mostly because I didn't redirect any cables), and the PSU is just mounted to the inside of the old PSU box... but I'm just happy to have something working. :o)

Edited by macosten

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9 minutes ago, Unknown_K said:

So you gutted and rewired a Q950 PS because of bad RAM?

No; there was no point in time when the stock PSU and the bad RAM were both installed at the same time. I figured I'd do both things at once... you'd think I'd know that I should only change one thing at a time by now.  I realize now I didn't make clear in my earlier post.

 

In my defense, I posted that way too early in the morning after spending way too much time getting it working... :o) 

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