I'm slowly going through the issues with my 7854, at the moemnt I'm chasing a problem where, after being on for some time, the mode selection switches stop working, all I get is a beep from the speaker and the readout flickers whenever I press a button. From cold it seems to work OK, although I also have a fault with the readout where all the characters are squashed vertically aalmost to a line. The CPU is still running as the bus is active, I'm struggling to figure out how the mode select works as it appears to drive the data bus directly, and the beep seems to indicate that the processor is seeing the button presses. Any suggestions where to start faultfinding this?
