Quadra 950 Power on and Off after A Few Seconds

[techstep]

Hi All,

I recently bought a Quadra 950 from someone on these forums. The computer was packed by UPS in a good box with plenty of bubble wrap and arrived without any external damage. 

However, the computer just doesn't successfully power up. The seller says it worked perfectly before shipped.  When turning the key to the 'run' position or when pressing the soft power button on the keyboard, the power supply starts to engage, and the fan spins for 1-2 seconds, and then immediately turns off. I also vaguely hear a hissing from either capacitors or an internal transformer? 

Here's a video for illustrative purposes:

https://www.dropbox.com/s/0u2cc1kiici74e1/Video Dec 07%2C 9 59 50 PM.mov?dl=0

I've tried unseating all peripherals, removing/reinstalling all the removable memory/vram, disconnecting all cable connectors to the logic board, etc. 

I've measured the power supply voltages where I could. Soft power 5V is there, 12V is on target, but the 5 volt rail  coming out of the hard drive connector to ground measures 0.55 volts, leading me to believe the issue may lie in the power supply. 

Anyone seen symptoms such as this before? I'll see if I can borrow a Quadra 950 Power supply from somewhere to test my suspicions, but would appreciate any other troubleshooting tips/insights you guys recommend.

Cheers!

 

[Sir Foxx]

I would also like to see why this failed. More than likely the power supply is going to have to get opened up to find the issue.

I've had the computer fully loaded with nubus cards and it never missed a beat. Not sure what might have got jostled to cause this issue. 

The package has insurance on it. I would pursue that since it arrived damaged.

 

[cheesestraws]

Just a couple of general thoughts, since nobody else seems to be chiming in:

1. The Q950 power supply is known... touchy, at this point, I think is fair to say.  I've never had one die on me yet (touch wood!) but the stories I've heard from other people have made it one of the few large spare parts I keep one of on general principle and test regularly.  I'm also very careful about how I plug and unplug it.  I realise this is of little use as advice, but it is hopefully context, at least.
    
   
2. @Sir Foxx's comment on load got me thinking: could it be that the PSU doesn't think it's got enough load, for some reason?  I know that some PSUs will turn themselves off after a few seconds if they don't think anything is connected to them, and/or will misbehave generally.  Could something have drifted out of tolerance in such a way?  Can you try putting more load on it and see if that stabilises it?
   

 

[ArmorAlley]

You are not the only owner of a Q950 to have trouble with the power supply.

A member of these fora — @BadGoldEagle — has been doing something about it.

Have a look at this great thread:

 

[Sir Foxx]

Just a couple of general thoughts, since nobody else seems to be chiming in:

1. The Q950 power supply is known... touchy, at this point, I think is fair to say.  I've never had one die on me yet (touch wood!) but the stories I've heard from other people have made it one of the few large spare parts I keep one of on general principle and test regularly.  I'm also very careful about how I plug and unplug it.  I realise this is of little use as advice, but it is hopefully context, at least.
    
   
2. @Sir Foxx's comment on load got me thinking: could it be that the PSU doesn't think it's got enough load, for some reason?  I know that some PSUs will turn themselves off after a few seconds if they don't think anything is connected to them, and/or will misbehave generally.  Could something have drifted out of tolerance in such a way?  Can you try putting more load on it and see if that stabilises it?
   

I doubt that its a load issue. The video he posted, its making some sort of hissing sound that I've never heard before when I had it. 

 

[BadGoldEagle]

Sorry guys for the lack of content on the site recently (BTW thank you @ArmorAlley and @ktkm for pinging me).

My PSU had a similar issue before it eventually blew up (powering a defective power supply can only damage it further): The 5V rail was completely dead (mine didn't hiss though, are you sure it's not the camera??). When connected to the Quadra, it kept power-cycling every second or so. Powering it outside the Quadra (by shorting the blue and the white cables together) kept it "stable" but the rail was still dead. I suspect some regulator on the primary "input" board is causing this problem but I have no way of verifying this (schematics are nowhere to be found, the original manufacturer just doesn't care), and having PSUs professionally repaired is not viable economically ($500+).

That's why I came up with the QuadrATX mod (still work in progress). It lets you use a standard ATX PSU and retains the original features (soft power etc...). You need to know what you're doing though if you want to give it a try. Otherwise, you can get an ATX extension cable and re-arrange the pinout to get your Quadra working temporarily. 

 

[markfendley]

Hi All,

I recently bought a Quadra 950 from someone on these forums. The computer was packed by UPS in a good box with plenty of bubble wrap and arrived without any external damage.

However, the computer just doesn't successfully power up. The seller says it worked perfectly before shipped. When turning the key to the 'run' position or when pressing the soft power button on the keyboard, the power supply starts to engage, and the fan spins for 1-2 seconds, and then immediately turns off. I also vaguely hear a hissing from either capacitors or an internal transformer?

Here's a video for illustrative purposes:

https://www.dropbox.com/s/0u2cc1kiici74e1/Video Dec 07%2C 9 59 50 PM.mov?dl=0

I've tried unseating all peripherals, removing/reinstalling all the removable memory/vram, disconnecting all cable connectors to the logic board, etc.

I've measured the power supply voltages where I could. Soft power 5V is there, 12V is on target, but the 5 volt rail coming out of the hard drive connector to ground measures 0.55 volts, leading me to believe the issue may lie in the power supply.

Anyone seen symptoms such as this before? I'll see if I can borrow a Quadra 950 Power supply from somewhere to test my suspicions, but would appreciate any other troubleshooting tips/insights you guys recommend.

Cheers!

Mine is doing exactly the same after I fumbled to push in a power cord which was connected to a socket already switched on. It looks like it might be the transformer labelled 'T1' inside. I am going to start replacing caps...