No good at documenting these but putting this here for just for reference.
The background for this was intermittently appearing and disappearing and it turned out to be a dodgy turned pin socket housing a ls32 at U7.
The sprites were very corrupted only half the lines were being drawn(stripey sprites)and double images appearing briefly now and then. Initially I consider the problem to be the 8 x D2125 rams so they were removed and sockets installed. Unfortunately all these rams tested ok in another pcb. At this point I remembered that I'd had this before on a dd bootleg years ago.
In this case the ls157's at E11 and F11 next to the D2125's had both gone faulty and replacement cured the problems. I will confess that I determined this by the old piggy back method which changed the faults enough to suggest it was worth replacing these.
Not a clever way of fault finding but for a quick fix without schematics,scope I got lucky.
I will also say that my cheapy Chinese 1.5v ic tester passed a lot of my 'pulled' ls 157's which were actually faulty. I did use this opportunity to test all my spare ls 157's,ls32's and the few D2125's I have.Anyway a fully working exerion bootleg once again back on the shelf.
The background for this was intermittently appearing and disappearing and it turned out to be a dodgy turned pin socket housing a ls32 at U7.
The sprites were very corrupted only half the lines were being drawn(stripey sprites)and double images appearing briefly now and then. Initially I consider the problem to be the 8 x D2125 rams so they were removed and sockets installed. Unfortunately all these rams tested ok in another pcb. At this point I remembered that I'd had this before on a dd bootleg years ago.
In this case the ls157's at E11 and F11 next to the D2125's had both gone faulty and replacement cured the problems. I will confess that I determined this by the old piggy back method which changed the faults enough to suggest it was worth replacing these.
Not a clever way of fault finding but for a quick fix without schematics,scope I got lucky.
I will also say that my cheapy Chinese 1.5v ic tester passed a lot of my 'pulled' ls 157's which were actually faulty. I did use this opportunity to test all my spare ls 157's,ls32's and the few D2125's I have.Anyway a fully working exerion bootleg once again back on the shelf.