Trouble Shooting a Galaxian PCB

Dlsmith

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Looking for some input on trouble shooting a Galaxian PCB.

Where I am at:

I'm teaching myself how to repair arcade PCB Boards. I have purchase a Galaxian PCB as my test project.
I built a test bench with an CGA/EGA/YUV/RGB to VGA arcade converter to make the process easier.

The PCB had the ROM mother board and I converted it to the single 27128 Eprom Modification.

On the reset pin 26 of the CPU I'm getting a high signal but it stays there. when I hit the reset button, it's high, briefly low, then stays high. According to my manual, it should start high, then stay low.

Does anyone have a suggestion of were to start looking.

Also, I have +5vdc at the CPU and the ROMS.

Attached are pictures of my PCB and the screen I'm getting now.

Thanks for any suggestions.

David
 

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the single rom program/wiring correct

is there any activity on the address/data lines of the cpu. try another z80 to rule out a bad cpu.

have you tested the ram see if you have any stuck of floating pins on the main 2114 rams

look for any damage on solder side of pcb

a vaild reset should start low then go high and stay high if its stuck low or goin from high low all the time means cpu is stuck in watchdog so if you think its wrong go back through the reset line in the trouble shooting manual should help in that area
 
Last edited:
Update:

I tried another Z80 and get the same screen.

Checking with my logic probe, I can trace the High/Low signal back to location 6S, a 7474 chip. I need to pull up that chip specs to check it further.
 
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