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S-100 board testing with Z-80 ICE
  by Bill Degnan - 12/20/2008 21:58
I just finished testing a Cromemco 64KZ RAM board. I did this by using Bob Grieb's Z80 ICE, which is made to be plugged into the Z80 slot of computer or controller card. Bob created his own "PIC-based circuit that could emulate a Z80 for displaying memory, writing to I/O ports, etc. as an aid to troubleshooting..." Bob's modern version is based on the Nicolet Paratronics Z80 emulator called the Z80 NICE. I am fortunate to have been given a beta version of this device to test.

I inserted his Z80 ICE into a Jade CPU card, which is installed in my California Computer Systems 2200 Series S-100 computer. Using the ICE I was able to determine that the JADE controller was working correctly. Next I tested 2 64K RAM cards a Cromemco 64KZ and a SMS 64K. The SMS was 100% OK, but not the Cromemco. Here is a snippet from the program output after first-pass testing of the Cromemco RAM card; these are example address locations that the testing program was unable to correctly write/read back:

1A1F- W:40 R:50
1B9F- W:42 R:52
1C9F- W:01 R:11
1D9F- W:02 R:12
1E9F- W:04 R:14
201F- W:EF R:FF
219F- W:20 R:30
229F- W:40 R:50
241F- W:42 R:52
251F- W:01 R:11
261F- W:02 R:12
271F- W:04 R:14
289F- W:EF R:FF
2A1F- W:20 R:30
2B1F- W:40 R:50
2C9F- W:42 R:52
2D9F- W:01 R:11
2E9F- W:02 R:12
2F9F- W:04 R:14
311F- W:EF R:FF
329F- W:20 R:30
339F- W:40 R:50
351F- W:42 R:52
361F- W:01 R:11
371F- W:02 R:12
381F- W:04 R:14
399F- W:EF R:FF
3B1F- W:20 R:30
3C1F- W:40 R:50
3D9F- W:42 R:52
3E9F- W:01 R:11
3F9F- W:02 R:12
etc.

Lastly I tested a mod-ed Cromemco ZPU board, but it does not detect the presence of either memory card. I am not sure why but the wait state jumpers have been changed. My instinct is to revert the card to the original configuration. The M1 jumper to 0 has been cut and it's instead wired to pin 4 of IC40. The voltages I think are OK and the computer itself is OK volts-wise.

more to come...

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More testing, Cromemco 64KZ
  by Bill Degnan - 12/21/2008 11:28
How do I interpret this, and what would cause only the "7's" to fail? Note above that the failure addresses are all "F's". I believe that when you see this kind of thing, it's not the memory, its a component that is failing, but I can't say for sure.

Small range tests are OK.

OK ===> mt 4ef0 4eff

OK ===> mt 4e00 4eff

OK ===> mt 4a00 4fff

Finally when I broaden the test to the entire 4 page, I do get some errors in the read write test:

OK ===> mt 4000 4fff
4957- W:80 R:81
4BD7- W:02 R:03
4CD7- W:04 R:05
4DD7- W:08 R:09
4ED7- W:10 R:11
4FD7- W:20 R:21

OK ===>

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Somewhat similar memory failure.
  by William Dromgoole - 12/23/2008 11:08
I once had a similar problem with odd results from a memory test on a board that I wire wrapped for an Ohio Scientific Super Kit and it turned out that power was missing from some of the memory chips. Apparently they were getting some power leakage from the data lines. It depended on what the data input value was for the chip to operate or not.

Good luck, Bill #3

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ICE and RAM may vary in compatibility
  by Bill Degnan - 01/09/2009 21:21
I have been told that it RAM controllers differ, some are more suited to a specific manufacturer and will work correctly in their intended environment. I do have an IMS 32K board that passes the RAM flawlessly so I do know it's possible to pass the ICE RAM test.

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