Several weeks ago, I found an Apple IIe lying in a pile of trash and broken furniture on the curb a few miles from home. I took it home and completely disassembled and cleaned everything, and replaced the RIFA filter cap in the power supply just to be sure. Other than the keyboard, everything seemed to be in good shape, although there was some corrosion on sockets and internal connectors.
When I powered it up everything seemed to be working properly for a few hours. Then, it started to develop graphical glitches. In normal text mode, I sometimes see white bars creeping down the screen, solid at the top and intermittent at the lower part of the screen. These are intermittent and normally not present. In color mode, when playing games, I see black bars on the screen, although they only seem to affect some colors.
RAM test succeeds, so I am suspecting the problem lies in the video ROM or something connected to it.
I removed and cleaned all the chips and sockets and re-seated everything. This fixed the problem for a few minutes before it returned.
Any thing else I should check before I start ordering replacement parts?