Defective C64 partially showing reversed characters

[nippur72]

Don't know wether to post here or in "other systems"...

Well, I have a C64 that doesn't show reversed characters in some zones of the screen. These zones are random in horizontal stripes. Some few locations are even blinking (switching rev on/off). This failure is very annoying because it causes the cursor disappear on most lines (because it doesn't blink). What could be the cause? I've opened the case and all seems ok. I removed the 6569 from the socket and put in it again, just to see if it was a failing contact but nothing changed. The failing locations sometimes change on power on/off.

Is there anything I can do to fix it?

This C64 was given to me by a friend whose uncle, a radio amateur hobbist and electronic repairman, sadly died last year. He also gave me two C64 home made cartdriges with radio amateur software and a "Noapack" packet radio unit that plungs into C64 user port.

[Richard James]

Is not the reverse bit for a character the highest bit in the byte? If so then maybe there is a problem with the memory chip or the connection to it?

You could test the memory with a small program.