Lisa 2 Board Troubleshooting

No replies
Offline
Joined: Jan 19 2014
Posts: 59

Hi everyone,
I have two Lisa boards that are currently not working for unknown reasons that I would like to get working. One is a CPU board, the other is a 2/10 I/O board. These boards came from a Lisa 2/10, and do not have corrosion damage. I have a functioning Lisa 2/5, and by swapping cards around, I was able to test these two boards. They behave as follows.
CPU board (installed in 2/5): After the power button is pressed, there is no sound/"pop" from speaker. Originally, it looked as if the screen was dark, but when the brightness was increased well above normal level needed on a functioning Lisa, the screen showed a gray screen with transverse/diagonal lines. When the reset button is pressed, the lines move upwards for a second or two before resettling back down to their previous position. Once in a while, the screen comes up to a "garbage" screen of random pixels when testing this board. Clicking the power button to turn off the Lisa does nothing. I am aware of the potentially leaky capacitor problem by the 68000 that asserts an infinite reset cycle if broken; I have ruled out the possibility of this being the case.

I/O board (installed in 2/10 with working CPU and RAM boards): My Lisa 2/10's CRT power board has something wrong with it right now, so the screen doesn't "stretch" vertically (it's just a thin line in the middle of the screen). However, the symptoms now are the same as what happened before the power board went crazy. When the power button is pressed, the speaker does "pop", as per usual. However, a second or so after this, the speaker "pops" continuously, about four times a second. I don't quite remember what the screen did during this, but I think it showed the top bar and ROM version, but nothing else. Again, pressing the power button does nothing to turn off the Lisa.

Note that the RAM boards have been verified working. I have cleaned the edge connectors of the cards as well as the legs of the chips, which I have removed and reseated. I have attempted in the past to replace each removable chip on each board with a working version from my working boards, to no avail. I do have another CPU board and 2/5 I/O board at my disposal that are severely corroded, but still have chips installed that may or may not be working, in case I need to scavenge any chips. I will be happy to provide pictures, if needed.

Does anyone have any idea of what's going on here? Any help would be greatly appreciated!