Quadra 950 Issues

[QuillOmega0]

So my Quadra 950 seems to have issues booting, especially when its cold in the room (I'm talking real cold like in the 50s). I can leave it running but after a while it'll power up, or I can heat up the room to the higher temperature and that'll allow it to bootup. When I run into this issue, it doesn't give any bongs or sad mac, the fans and drives do spin up though.

I suspect the reset and interrupt buttons as a culprit as when I even lightly touch it it'll trigger their respective functions and I had the interrupt switch get hit on its own.

I am right now checking the resistance on the interrupt switch while heating up my room to see if the mac will power up and if the issue is indeed that. I"m right now showing 10-20 ohms. Ideally I should be showing infinite resistance, but I don't have anything to compare that to so I'm not sure

For the people with Quadra's out there, can you please measure the resistance on the leads of the switch so I have something to compare it to?

To the others, what are your thoughts and suggestions.

And yes I do really keep the room this cold.

[Bunsen]

Sounds like an intermittent open circuit to me - a break in a trace, solder joint or lead that expands and makes contact when it is warm enough. Wild guess based on the behaviour you've reported. Intermittents are a bear to track down - if you have a hot air gun or hair dryer and a can of freeze spray, that can help you zone in on the general area, but in the end it'll be poring over the board with a good magnifier that'll show you the location of the fault - if that's what it is.

[QuillOmega0]

I jammed a piece of paper into the interrupt button and that allows me to boot the mac, I'm still doing some experimentation

[trag]

IIRC, the 68040 is socketed on that model. I would (very gently and carefully) pop the 68040 out of the socket, inspect the chip and socket, and then reinsert. It could be that there's a little bit of corrosion getting the way, and the rubbing of removal and replacement will probably take care of it.

It won't definitely take care of the problem, but it's a cheap and easy thing to try. Similarly with the SIMMs and VRAM, although problems with those should still allow for a good start up bong, followed by some kind of error or crash.

[dpny]

Back when I had my IIcx I would run into this problem, and apparently it was the drive: when it got cold, whatever was used to lubricate the drive mechanism gave a little too much resistance for the motor to spin up.

[Bunsen]

Hah. That would possibly explain the heating element I found in the bottom an old Prime Data mainframe/minicomputer disk rack case.

[dpny]

Yep,

The solution was to wait a few minutes for things to warm up.

[QuillOmega0]

FIxed it temporarily by wedging a screwdriver into the interrupt switch. Not the best fix, but it'll do.

[QuillOmega0]

Until now, I decided to do it proper and pulled the logic board out. Good news is as far as I can tell the logic board is fine, buttons are fine and responsive. I put it in the case and buttons feel much better now. I suspect the logic board's latch to hold it in place wasn't latched properly by the previous owner and the board drifted forward just enough to cause this issue. But I'll have to leave it until tomorrow before I confirm that theory.