1979 Atari Asteroids - RAM error

[Teh_Commanderer]

     I recently began working on my secondary PCB, It was missing the vector RAM, X-Stal, ceramic cap, when I bought it and I did notice that one of the 3 ROMs was a duplicate of the 2nd ROM. I installed a new crystal and cap and 'borrowed' the vector RAM and Game ROM from my other PCB for testing. I have reflowed the vector and sound area of the PCB and stopped there. This was a board that I used for parts for my primary, mainly all of the 2114's, I since ordered parts from Bob and decided to finally get this one working. The problem now is when I power it up I get the classic ROM error tones of 'beep-beep-BOONNGG!' which indicate that the RAM in area M4 has failed the test, however, I switched the first RAM with the 'failing' RAM and get the same error tones > So that rules out that the RAM in that spot is bad. I vividly remember having the same problem as before, but that had a R4 error instead, the next step I took was a reflow.

[TheGuru]

well think about it for a minute, your PCB is almost 40 years old....
probably you have a logic fault with the RAM address/data logic.
I think the schems are available so study the schems to find the chips connected to the RAM and start there.
work backwards checking input/output pins on the logic chips until you find the issue.