Power Mac 7600: Black screen after inactivity

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Level 1

21 points

Power Mac 7600: Black screen after inactivity

Hi all, this is a Power Mac 7600 OS 8.6 question…

This computer is starting to have video issues. I use a vga card instead of the standard video port (not functional).

Here’s what’s happening…

This is obviously a hobby computer which doesn’t get powered on every day, but I do leave it plugged in all the time. It is starting to give me the black screen at startup if it hasn’t been powered on for a week or so. New battery, zapped the PRAM several times to get the screen on. If I power it on every couple of days there’s no issues.

It’s as if this randomly occurs if it isn’t used for an extended period of time.

Thoughts or suggestions? Thanks!

Posted on Jan 1, 2026 2:12 PM

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Answer 1

Top-ranking reply

HWTech

Level 9

69,134 points

Jan 1, 2026 5:52 PM in response to beigebox

Have you tried resetting the CUDA chip?

I found an Apple Service Guide which shows the CUDA Reset button is located on the Logic Board near the ADB port & the Audio jack. Unplug the computer and open the tray like you did for replacing the battery. Press the CUDA Reset button. Personally I would wait 15 seconds before attempting to power on the system (just habit probably for later PMC/PMU Resets).

http://www.applerepairmanuals.com/the_manuals_are_in_here/PM7300_7500_7600_WS7350.pdf

This service guide should give you everything you need to know about trying to power on and boot the system. You may also want to review the PRAM Reset instructions as well.

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Answer 2

Jeff

Level 6

12,322 points

Jan 2, 2026 2:40 PM in response to beigebox

You should remove the PCI graphics card and inspect the gold-plated pins for discoloration. If you have a soft, white eraser, you can gently scrub both sides of the pins to restore a bright appearance. Be sure to blow off all rubber shavings before installation. Have you tried switching it to a different PCI slot? If the problem persists, the card might have an intermittent component failure on the PCB. Are you using an ATI card?

As for the onboard graphics, what caused it to fail? Do you have matching 1 MB VRAM cards installed in paired (alternating) slots?

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Answer 3

Limnos

Level 10

427,631 points

Jan 1, 2026 2:36 PM in response to beigebox

You're leaving it plugged in all the time too? To me it sounds like the battery. I didn't know they even still sold those.

The only way to test the card is basically swap it would for a known working one and see if the problem persists. The same for other components such as the cable and display.

The card is seated properly?

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Answer 4

beigebox Author

Level 1

21 points

Jan 2, 2026 3:24 PM in response to HWTech

Thank you for sending the repair manual link. I’ve completed the cuda reset, logic board reset and installed a fresh battery.

Working just fine at the moment. I think I will wait 2-3 days to power it up again to see if the black screen goes away

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Answer 5

beigebox Author

Level 1

21 points

Jan 2, 2026 3:27 PM in response to Jeff

Thanks Jeff. Turns out the video port works using a quality adapter. I’ve just been using the pci card because I didn’t have a good adapter until today.

I’ve cleaned the pins per your suggestion. Going to wait 2-3 days to see if the black screen issue is solved

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Answer 6

beigebox Author

Level 1

21 points

Jan 2, 2026 3:21 PM in response to Limnos

Thanks for the reply. Yes I checked and cleaned the gold contacts and seated it properly. It’s 1997 vintage so anything is possible here!

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