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  Vector Graphic ZCB by Bill Degnan - 06/20/2010 12:08
The Vector Graphic ZCB is a S-100 single board computer. Not working at the moment. Here is an outline of the work done.

1. Set up a Northstar Horizon with standard cards, working drive, working CP/M disk, verified boot works, etc.

2. replaced N* CPU card with the VG ZCB. It actually worked once, but only once. The ZCB is supposed to send a dot prompt to the terminal. When one enters B, it looks for the northstar drive controller, and boots the disk.

3. set up a breakout box to the RS232, learned that the system was not sending a detectable CTS or DSR. These are the signals sent by the N1489 driver chip. The voltage is 10V, should be 12V.

4. There are two 1K ohm resistors in R22, R23 that are only measured to be .9K, so something is reducing the resistance. When I pulled these two, they returned to 1K, so the resistors themselves are OK.

5. Replaced the 1488 chip. No improvement

6. Removed the 104 m54 cap in C-20 near the 1488. no improvement in the measured resistance on R22 and R23 resistors.

7. tested the other resistors, they're all ok.

8. Built a new serial cable, tested OK.

9. Tried a new Z80 chip. no improvement.

10. Used an in-circuit z80 emulator to verify the ePROM is correctly writing code to E000.

Conclusion? Not sure. Do I try removing the 1489 see if that's the chip shorting the system? I need to find a 104m54 cap for C-20. basically there is a short someplace.

Vector Graphic ZCB User's Manual

  ZCB Update 10V too low for DTR/RTS by Bill Degnan - 06/27/2010 15:19
- replaced both 1488 and 1489.
- did my best to repair a cut trace from the UART DTR signal, not sure why the cut was there, perhaps previous owner was trying to find the short and cut the trace?
- Replaced cap in C20.
- Verified that the 1.0 K resistors in R22 and R23 are OK, but when tested on the card, something is causing them to only report .9 K

- Tried a different UART, no change.

I am not sure what to do at this point, but perhaps there is a short on the card that is too small for me to find and fix. So I will keep working on it...

  ZCB replacement by Bill Degnan - 07/10/2010 10:14
I was offered a replacement card, but it never materialized. This project is on hold at the moment...



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