Dead Galaxian

Motoman202

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Donor 2021
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I have a Galaxian PCB that won't show anything whatsoever on the screen. Pin 26 on z80 is toggling so I jumpered the pads to disable the watchdog. I have good clock signal. I also swapped out the z80 and put in the Galaxian test rom. Only get a steady tone out of the speaker (which I think is normal with the test rom but can't remember) and still nothing on the screen. Not sure where to go with this one?
 
After swapping the 2114 ram out the board is no longer tripping the reset line. Still nothing on the screen. Activity on address lines with the acception of pins 37-40 and data lines are mostly high with pin 13 low. PIN 19 MREQ is active.

These lines are all high
17 NMI
18 HALT
20 I/O REQ
23 BUS AK
25 BUS RQ

This is with the Galaxian test rom.

Not sure where to start on this one.
 
After swapping the 2114 ram out the board is no longer tripping the reset line. Still nothing on the screen. Activity on address lines with the acception of pins 37-40 and data lines are mostly high with pin 13 low. PIN 19 MREQ is active.

These lines are all high
17 NMI
18 HALT
20 I/O REQ
23 BUS AK
25 BUS RQ

This is with the Galaxian test rom.

Not sure where to start on this one.

/NMI should be firing if it's not disabled by the '259.

The other lines aren't used.
 
The test ROM disables /NMI until it's completed the work RAM test so if it doesn't complete that successfully then /NMI won't fire.

That said, I don't believe code is running properly anyway. First off, re-enable the watchdog and see what the computer part of the circuit is really doing.
 
The test ROM disables /NMI until it's completed the work RAM test so if it doesn't complete that successfully then /NMI won't fire.

That said, I don't believe code is running properly anyway. First off, re-enable the watchdog and see what the computer part of the circuit is really doing.
Watchdog jumper removed. Cpu reset line low then stays high no longer reseting. Cpu activity same as above.
 
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