Problem: ~RESET (6809 pin 37) is always low.
All the chips in this system work fine in another system.
R208, C228, C229, D201, and R201 are all good.
Everything in the schematic that is supposed to be on the RESET circuit is connected, and I've done a thorough search for shorts to anything in the RESET circuit.
The RESET switch has been temporarily replaced with a known-good switch.
So... If I pull the 6809 and power up the logic board, RESET behaves as expected although seems to be at 4V (need to compare this to another machine to see if that's expected--5V supply is a steady 5.0V). When the 6809 is present, RESET is "magically" driven low. I say "magically" because I can't find any frickin' way the presence of the 6809 should cause that. This CPU works in another machine, and I can see a valid 6mHz clock input, and 1.5mHz clock from the CPU. Maybe I've missed something in the 6809 specs?
Any suggestions appreciated!
(also posted on /r/Vectrex on reddit, but I think there are more technical people here)
All the chips in this system work fine in another system.
R208, C228, C229, D201, and R201 are all good.
Everything in the schematic that is supposed to be on the RESET circuit is connected, and I've done a thorough search for shorts to anything in the RESET circuit.
The RESET switch has been temporarily replaced with a known-good switch.
So... If I pull the 6809 and power up the logic board, RESET behaves as expected although seems to be at 4V (need to compare this to another machine to see if that's expected--5V supply is a steady 5.0V). When the 6809 is present, RESET is "magically" driven low. I say "magically" because I can't find any frickin' way the presence of the 6809 should cause that. This CPU works in another machine, and I can see a valid 6mHz clock input, and 1.5mHz clock from the CPU. Maybe I've missed something in the 6809 specs?
Any suggestions appreciated!
(also posted on /r/Vectrex on reddit, but I think there are more technical people here)