- Joined
- Nov 29, 2005
- Posts
- 4,275
Hmmm...
In working on a 4 slot board (MV4F) I encountered a Z80 error.
The board had other issues (documented elsewhere) and when those were fixed and the board not yet reassembled, it gave a Z80 error.
The reset line was held high.
The reset line goes through the 74AS245 IC at location E11. It goes through the latch on pins 2 and 18. If that IC is bad the reset line could be stuck high or low, causing the Z80 CPU to never boot.
That reset line must transistion from low to high to reset the Z80 CPU and make it start executing commands.
In this case the problem came because the IC at E11 was pulled from the board as a step in troubleshooting. Once the IC was placed back in the board the reset line cycled normally and the Z80 booted. (This was also tested by jumpering the reset line on pin 15 of IC A9 to pin 26 of the Z80 before replacing the IC)
Enjoy!
RJ
In working on a 4 slot board (MV4F) I encountered a Z80 error.
The board had other issues (documented elsewhere) and when those were fixed and the board not yet reassembled, it gave a Z80 error.
The reset line was held high.
The reset line goes through the 74AS245 IC at location E11. It goes through the latch on pins 2 and 18. If that IC is bad the reset line could be stuck high or low, causing the Z80 CPU to never boot.
That reset line must transistion from low to high to reset the Z80 CPU and make it start executing commands.
In this case the problem came because the IC at E11 was pulled from the board as a step in troubleshooting. Once the IC was placed back in the board the reset line cycled normally and the Z80 booted. (This was also tested by jumpering the reset line on pin 15 of IC A9 to pin 26 of the Z80 before replacing the IC)
Enjoy!
RJ