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Problems with Z80 DART serial

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I made a PCB for Grant Searle's Z80 CP/M computer.

I have had a problem I can not figure out. When I turn on and reset the computer from a cold start after not having applied the power for awhile, the computer seems to operate just fine. I can boot up CP/M and use it for about 2 or 3 minutes. However, after 2 or 3 minutes, CP/M starts to show BDos errors and directories appear with duplicated filenames. Shortly afterwards, the computer stops accepting serial input, though if I reset serial output occurs (it displays the "Press [SPACE] to activate console").

I have removed the compactflash card and all of the chips I added to the design and the problem still happens. I thought it might be that I was using the Z80A DART, so I bought a Z80B DART, but that did not help.

If I unplug the computer and allow it to stay unplugged for a few minutes, the computer is fine again for a few minutes. Maybe its a heat problem, but none of the chips get more than slightly warm.

If anyone could provide advice on how to track down such an intermittent problem I would appreciate it. The schematic for the Z80 computer is in the github project.


Andy Watson:
It does sound very much like a thermal problem. Is the power-supply holding up? Take a can of freezer, or other cooling agent (alcohol ?) and check each chip in turn.

Simple idea: Try putting an ice cube tray directly over/under the board.
If that helps it run longer, then definitely thermal.

Or, as Andy said, monitor PS voltages during that first couple of minutes, to see if anything changes.


Well, I placed a beer can on the Z80 processor and now it seems to work for awhile.

The conclusion is naturally, my processor wants beer.   ;)

Or, the beer can is cold and cooled the processor.

Well, a Z80 overheating? I don't think I've ever seen this.
Or maybe the board itself is heating for some reason, and in turns heats the CPU...


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