Received from Portugal a faulty Nemesis PCB for repair, actually a conversion from Konami GT on GX400 hardware.Set is made of a CPU board :
And a VIDEO board :
The game was full playbale with sound but the graphics were glitched as there were jail bars all over the screen:
The fault was obviously located on the bottom VIDEO board therefore first of all I ruled out all the custom ICs by swapping them in a good board, they were all OK.Then I focused on a couple of rows of 4164 dynamic RAMs (some were already replaced) :
They are 64K x 1-bit devices, here’s pinout :
On this board they are used as sprite line buffer like schematics show :
I went to probe them with my scope and I found one with an unhealthy signal on data output pin (good signal for comparison on left of below picture) :
It was the chip @5H which I prompty removed and replaced with a good one :
This fixed the issue and board competely.Repair accomplished.
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