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Macintosh Quadra 840AV Post Issues


Well-known member
The 840av PSU uses the same pinout as the IIci/Q800/IIcx etc I believe, so if you have any working ones of those that would be another way to test.
This isn't right, they use the same PSU as the 8100, and you can get away with an 8500 or 9500 PSU, by leaving out the secondary connector.


Well-known member
The motherboard is back with its owner. He's going to try with a power supply from the 8500. I wasn't able to figure it out but it was posting most of the time. Hoping it's the power supply.


Well-known member
First off, thanks to @jmacz for the repair work on this board. It's in WAY better physical and operational condition than when I first got it.

After a busy week at work I finally had a chance to spend some more time testing this board.

From a cold start (ie no power for over a couple hours) in 70F/21C weather , the board turns on with soft power and gets no chime and no display.

However, after I leave the board powered on for ~5 minutes and reboot it, I get a chime, grey screen, and blinking question mark 100% of the time I tested this. Any subsequent reboot thereafter instantly produces the chime/grey screen. Sample size of about 15 over 3 days. Trying an 8500 PSU produced the exact same results.

Anyone have further ideas why a cold boot could lead to the symptoms noted above? Once the machine boots to the grey screen when a SCSI2SD is attached, I can load Mac OS successfully and everything works great.


Well-known member
Hmm, that rules out the PSU.

Can you try this? After a cold start situation, try using a hair dryer to warm up the area around the VLSI (428631) chip (between the DIMM sockets and the CPU). And then try “cold starting” after that area is warm?

At this point my best guess is a slightly disconnected connection somewhere.