Super Pang (Jamma) Repair

Received a dead Super Pang jamma board sometime ago along with a heap of other faulty boards. Had played the game on Mame a lot so was keen to try and get the board working again.

This board was one of Capcom's earlier attempts of a "Suicide board",  basically all or part of the ROM set was encrypted and the encryption keys stored on battery backed volatile memory so when the battery died you lost the encryption keys.
Thankfully much work has been done to bypass this, The Dead Battery Society has full details on the modifications needed to board as well as the decrypted ROMs needed.

Following their instructions I was able to get the board up and running again. However there were problems with the background colours, which got worse over time as the board heated up.

Not pretty but works

Background saturated with 'Red'

Was unable to find any schematics for this board but did find another repair log for a similar fault. Sure enough the same RAM at 8C was the problem as in the other repair. Swapped out the chip for another one resolved the problems with the colours.

New RAM at 8C fitted

Proper colour restored

Colecovision Repair

Got a Colecovision for repair which had not worked in a few years. Had never seen or worked on a Colecovision before so had to do a bit of research on the typical failure modes. 

Top of the list were a faulty power switch and the video RAM as possible suspects. The power switch had already been changed and the VRAM replaced on the unit, the older 4116 RAM chips upgraded to single supply 4164 devices.

Measured the 5V rail across various chips at ~200mV, so something obviously pulling it down. VDP TMS9929A at fault here, replace the VDP and signs of life at last. 

Where's the Kong ?

Unfortunately a bit of garbled mess still. Ran a continuity test on the VRAM address & data lines turned up a couple of broken tracks. 

The 4164 RAM was soldered to the board when the previous upgrade was carried out, decided to remove all the RAM to check out the tracks properly and refit the RAM in sockets. On inspection the board was quite burned under of the RAM chips, the original 4116 IC must have badly overheated at some point.

Repaired the broken tracks,fitted the RAM in sockets, replaced the RF output with AV output and the Colecvision lives to fight for another day :)

Ah there he is..

Double Dragon (Jamma) Repair

Picked up this faulty Double Dragon board, no audio was the fault description. Sure enough game played through to the end in perfect silence.

Quick visual inspection highlighted a couple of missing caps and the rest of electrolytic's looking a bit tired. So after the board was cleaned up the capacitors were replaced, still no audio so time to poke about further.

Once I read or heard somewhere that you should use all your senses when debugging electronics, so with that in mind I set off.

Touching the audio amp produces an audible hiss, good sign the amp is working then and the problem is upstream. Further poking about and noticed the 68A09 was running pretty hot, check on the schematics showed this as the audio CPU so good chance this is the culprit. Verified the CPU as knackered with a scope.

Desoldered the old part and fitted a new CPU along with a DIP socket. Result. We've got audio again :)

Played through the game again just to verify, but still not near the 1CC level yet !!

New 68A09 installed