I was wondering whether anyone had seen a screen display like this before. This is a later type Vic 20 (cost-reduced). There is a black screen for part of the time, then occasionally these staggered, dotted, horizontal lines appear and remain static for a while before disappearing again:
The tape drive motor runs, but runs continuously. Issuing blind sound commands does not produce sound, but there is a slightly perceivable change in the low-level white noise from the TV (although maybe I'm imagining this). Cartridges do not work.
I've swapped all of the ICs out to a test board, four in total were faulty, they were replaced so that now all of the ICs tested good on the other board. It is now 100% socketed, so a problem with the sockets cannot be ruled out.
I've had the computer in question since 1983. It was put into storage in about 1984 after it stopped working. When I started to investigate recently, it appears that the PSU went bad and this was responsible for the original damage. I'm just stating this in case that has a bearing on the probable cause.
Since I'm probably onto getting stuck in with a multimeter or scope at this point, is there anywhere in particular that I should look? Are any other components known to fail and cause this kind of display?
Thanks very much for any help.
Chris.