Apple IIe Character Display Issue

[RHopple]

I recently received an Apple IIe from a friend who was cleaning out his house. It was decent condition but quite dirty, so I cleaned it well. My problem now is the display, specifically what it displays. The computer powers on to the basic prompt and beings displaying random characters. Eventually it will hit return and the computer will beep with a syntax error. At first, I assumed a keyboard problem. But after a few minutes, I unplugged he keyboard cable while the computer was on, and the random characters continued to appear. The issue, therefore, must lie in the circuit board or ICs. I have pulled, inspected and resocketed all the ICs carefully. I thought it may be a bad RAM chip or keyboard decoder.

In the picture below, the keyboard cable was left in for 5 seconds then removed. As you can see, it types characters without a keyboard even inserted. Any thoughts on what this might be?

View attachment 50507

 

[mwillegal]

I've seen this, with marginal I/O cards plugged into an Apple IIe. First thing to do, is to unplug all I/O cards and see if the symptoms persist.

regards,
Mike Willegal

 

[RHopple]

I actually determined that the AY-3600 chip was faulty and swapped it with one in another Apple II and the issue disappeared. Now the problem is the issue persists on the second machine. I'll have to look on eBay for a replacement part.