omegaman
Active member
I have another set for repair, from Member GoldenAge. This one looks very clean.....but don't let looks deceive you!! 
I pulled all the chips, all the Ram checked out good, apart from the BBU ram. The Roms and CPU were also fine. I could see by looking inside the sockets quite a few needed replacing. In the end i replaced 6 program Ram sockets, 1 Video Ram socket and 2 Video Rom sockets.
The board was now in a state to test
I powered the board up and it reported all Ram were bad
I checked the program Ram, selector IC at PN2 with the comparator.
sure enough it was bad!
Self test then passed the program Ram but failed the video Ram and Rom. I checked the 74245 at S1 (Video buffer) and that was bad as well.
I now had the Roms passing but all the video Ram were still showing bad. I checked the 7432 at R1, this is the selector chip for the video Ram. Again it was bad.
I pulled all the chips, all the Ram checked out good, apart from the BBU ram. The Roms and CPU were also fine. I could see by looking inside the sockets quite a few needed replacing. In the end i replaced 6 program Ram sockets, 1 Video Ram socket and 2 Video Rom sockets.
The board was now in a state to test
I powered the board up and it reported all Ram were bad
sure enough it was bad!
Self test then passed the program Ram but failed the video Ram and Rom. I checked the 74245 at S1 (Video buffer) and that was bad as well.
I now had the Roms passing but all the video Ram were still showing bad. I checked the 7432 at R1, this is the selector chip for the video Ram. Again it was bad.




