Performa 550 won’t boot (bad logic board)

[matj283]

I have a performa 550 that doesn’t boot. When I hit the power button, the led comes on and the fan and HD spin up, and there are 7 short beeps or clicks that I assume are from the hd, but there is no chime and no picture. I know the problem is in the logic board as it works with a color classic board. The board itself looks excellent. It’s been recapped and the battery has been replaced. Cannot see any signs of corrosion. I’ve got an oscilloscope if anyone has any ideas for testing.

 

[matj283]

Video of boot attempt: https://drive.google.com/file/d/1JUuOsrfCgbghXfd5S4OW6uJhquum3Sss/view?usp=drivesdk

 

[croissantking]

The HD sounds like a Quantum with stuck heads due to a sticky bumper.

 

[matj283]

The HD sounds like a Quantum with stuck heads due to a sticky bumper.

That’ll be an issue for another time. Right now I’m not getting anything on the screen and no chime

 

[matj283]

Through probing I found out that the 68030s reset pin is being held high indefinitely. Still don’t know what’s causing this.

 

[matj283]

All lines between cpu and rom are good, no broken traces

 

[matj283]

With ROM removed, address lines are "walking the bus" but with ROM installed, there is no activity on the address lines

 

[dkjones96]

Pin held high indefinitely on an 030 Mac is almost always leaky caps around the sound chip freaking it out.

The sound chip on these is in charge of reset.

 

[matj283]

Pin held high indefinitely on an 030 Mac is almost always leaky caps around the sound chip freaking it out.

The sound chip on these is in charge of reset.

68030 data sheet says reset is active low, so this wasn’t an issue. Dfac and cuda are clean. Absolutely 0 evidence of leakage or corrosion on this board