Hammerin’ Harry (Irem M81) repair log

Received for repair an Hammerin’ Harry PCB on Irem M81 hardware (it can be found also on M84).

Set is made of a top CPU board:

And a bottom VIDEO board:

The PCB simply booted to a static garbage screen:

The NEC V30 (uPD70116) main CPU was active on its data/address busses but when I probed the program ROMs I found a couple of stuck address lines :

Looking at hardware I figured out there are some 74LS373 used as latches to address the program ROMs :

Probing the one @IC39 revealed some outputs were floating while inputs toggling:

Once removed the chip failed the out-of-circuit testing :

I replaced the chip and the board booted up but on self-test showed most of times  a ‘RAM NG 8’ message:

Then it entered in game which was playable with sound but background colors were wrong :

The ‘KNA91H014’ surface mounted IC on bottom board @IC1 generates the palette for this part of graphics:

Its pinout/implementation from R-Type schematics :

I made a visual inspection and found a couple of lifted pins on a row:

I reflowed the whole IC with result that self-test no longer complained and graphics were fully restored:

The last issue I had is that some inputs were not wotking but I quickly pinpointed it to a missing custom resistor array near the JAMMA edge connector:

 

Having no spare I replaced it with a reproduction of mine:

Repair accomplished.