Dec 302018

I received for repair a quite rare original Spelunker PCB (on Irem M62 hardware).Board is a three stack one made of a top board (which carries most of sound hardware) :

SOUND board

A middle CPU board (specific for each M62 game) :

CPU board

And a bottom VIDEO board :

VIDEO board

The PCB had severe GFX faults, the sprites were only lines vertically stretched all over the screen:

All the sprites circuit lies on bottom VIDEO board which is the same for all games that run on M62 hardware.Looking at Kung-Fu Master schematics I could figure out that data bits from sprite ROMs are fed into the custom marked ‘KNA6034201’ :

Custom ‘KNA6034201’ in DIP40 package
Custom ‘KNA6034201’ schematics

The inputs were all active but most of outputs floating:

So the custom was most likely internally faulty.Luckily I have done a reproduction of this component some time ago.You can think of it like a 24-bit parallel to serial shift register:

I removed the custom and installed the reproduction:

‘KNA6034201’ repro

The sprites were back but not perfectly as they were lacking of lines and misplaced too:

Sprites not yet perfect…

The sprite line buffer consists in two 2k x 8-bit static RAMs (Toshiba TMM2018 used here) :

Sprite line buffer

Probing them revealed on both a floating address line (pin 1, A7) :

Address lines are generated by the surface mounted custom ‘KNA6074601’ :

Custom ‘KNA6074601’

Its pinout/implementation from Kung-Fu Master schematics :

I had no other choice than replacing this part so I asked the owner to look for a donor board.He found and sent me a Vigilante PCB which carried the ‘KNA6074601’ on bottom board :

Vigilante donor board

I removed the faulty one and soldered the spare back :

‘KNA6074601’ reworking

This restored the correct sprites:

Sprites and board finally fixed

Board 100% fixed.Job done.

 Posted by at 10:07 pm