'Tis Dead, My Jr.

[cebuscapucinis]

I posted this in vintage-computers.com but maybe the users here will give me something else to try.

I recently purchased a Jr off eBay that is not functioning. Display plugged in, turn the system on, nothing. I get a white screen, nothing else, and a constant hum/beep sound. I have disconnected everything and tried "bare run" but it still does the same thing. Disconnecting the disk drive controller causes the drive to spin up, so I know that that peripheral is working. The machine has two 128kb sidecars on it with the additional 64k internal. Disconnected those. Still nothing.

I posted pictures on the other forum but there doesn't appear to be anything abnormal on the board. I don't have access to an oscilloscope and wouldn't know how to use one and a multimeter, although I know how to use it, is out of my reach for the time being.

Are there any fixes that might work short of running traces to see voltages?