Jul 232014
 

A friend of mine sent me this really mint original Konami GT PCB saying it suffered from vertical stripes across most part of screen.

Konami_GT

 

Fired up the board and …he was right 🙂

Konami_GT_isue

 

Initial test said all RAMs were good so the problem was elsewhere.Without any schematics I started my visual inspection as usual.I noticed that the only IC replaced on this mint PCB was a 74LS157 @H13.Since a socket was installed, I removed this IC and all the part of graphics affected by stripes disappeared so I started to think problem was generated after this part of circuit.In particular I traced an output (pin 7) of this 74LS157 to pin 4 (RAS) of some TMM4164 DRAMs (there are 16 of them).Probing these DRAMs with my logic probe revelaed that on four of them pin 2 (DATA IN) was pulsing but the pin 14 (DATA OUT) was stuck high.So I desoldered (they were @G2, G3, H4, H5 position)  and test them in my Hi-Lo Systems ALL-07A programmer and the result was this:

TMM4164_testing

They all failed miserably.I was lucky since had  some good  4164 DRAMs taken from a scrap PCB in order to repair a Commodore 64 motherboard.Installed them and goodbye stripes for ever!Board 100% fixed.

Konami_GT_fixed

 Posted by at 10:18 pm