Quadra 950 failure

[ZTEX]

Hello I have a quadra 950 that seems to be dead.

The symptoms are, fans run, drives spin up, no boot chime, no display, reset and nmi do nothing, and keyboard pram reset does nothing.

What I have done already in diagnosis, test the ram (they all passesd on my simmcheck), replace the processor, install VRAM, reset pram, use a different pram battery, both key switch positions, PPC upgrade card, no PPC upgrade card, Nubus video card, no Nubus video card, unplug everything except the power supply switch and speaker.

If anyone has a suggestion on what might be wrong or what I can try or what I can test with an oscope and or multimeter, I would greatly appreciate it.

 

[uniserver]

can you test the +5 +12 / -12 rails and see if the psu is putting out the correct voltages?

 

[ZTEX]

I will do that, I assumed that because the drives spun up those are fine.

 

[ZTEX]

Ok the +5v, +12v, and -12v are within range, the only concern is pin 13 (white) to DC Ground is 3.89 VDC (is this the trickle power for start?)

 

[ZTEX]

New symptom, I left the quadra 950 on the I switch position but did not push the power button on the keyboard for a few minutes, when I did the speaker made a wimpy ping noise that faded out, almost like it tried to chime.

 

[ZTEX]

Waiting even long results in the monitor flashing for a brief moment.

 

[Unknown_K]

Are you sure the RAM is in correctly? 2 SIMMs on the top row, 2 underneath (4 needed at a time).

 

[ZTEX]

Yes, the banks are 2x2. I found some corrosion on pins of what I believe to be the frontside and backside bus chips, I tried cleaning them up and took high res up close photos to look and see if traces or pins were disconnected.

 

[ZTEX]

I guess I'm going to have to scrap the mobo and sell the good parts, ugh I really wanted to add the 950 to my traveling museum.

 

[BadGoldEagle]

Before doing that you should at least try washing the board. 

Even if the Q950 has tantalum caps, these can go bad sometimes. 

From a n00b point of view (I don't own a Q950), I'd say those caps need to be tested because a single bad cap can cause voltage variations.

Since I(t)= C. dV(t)/dt, intensity is also changing. If intensity and voltage aren't right, it can't boot up, right?

The display could be damaged and the speaker as well maybe? Can you test the monitor on another mac?

 

[olePigeon]

Sounds like bad caps, even if they are tantalum.

 

[ZTEX]

Before doing that you should at least try washing the board.

Even if the Q950 has tantalum caps, these can go bad sometimes.

From a n00b point of view (I don't own a Q950), I'd say those caps need to be tested because a single bad cap can cause voltage variations.

Since I(t)= C. dV(t)/dt, intensity is also changing. If intensity and voltage aren't right, it can't boot up, right?

The display could be damaged and the speaker as well maybe? Can you test the monitor on another mac?

Which surface mount caps on the board do you recommend I test?

No the monitor is a good working fixture monitor used to test macs with.

 

[ZTEX]

Sounds like bad caps, even if they are tantalum.

It does but I hardly know which of the 100s of them to test...

 

[beachycove]

Actually, I once plugged a jerry-rigged molex power splitter into a drive in a 950, following which a drive component blew with magic smoke, the machine shut off, and it would not start again, with the symptoms described.

I was unable to get it going, try as I might, but it must have been pram-related. I left it in a 'to be revisited' pile, sans power, and then tried again on spec one day, whereupon the darned thing booted right up. It is still fine years after, though hours of fiddling could not cure it at the time.

 

[ZTEX]

Ahh well see mine has been in storage for years faithfully waiting it's turn to be tested and refurbished. So it seems like I had the opposite happen, worked before storing and now is a fussy baby.

 

[ZTEX]

Further testing resulted in magic smoke on some surface mount transistors which put that Mac on the beyond repair broken but do not chop area. (It sits in the corner of shame)

 

[billymade]

Why not; have the mobo repaired/rebuilt? The member; techknight seems to have a high success rate and you might ask if he is willing to tackle the job!  :beige:  There is nothing more annoying; than having one of the baddest Macs ever made; sit in the corner, broken!  [ !] If you are going that route; you might send the power supply with it, see if it needs rebuilt as well. Looking forward to a success storey with this!  [] ]'>