PCB Repair Logs The Combatribes
OK Got this of Ebay as not working.
A thorough check of the PCB revealed a burnt track near IC104 (ROM near 3rd player connector) this was caused probably by the fact that two pins had bent over and contacted on the back of the PCB. This damage showed up on the screen as horizontal lines of black the white bars and thats it.
Also noted was the custom IC33 had a gouge on pin 61 cutting the track.
Its worth mentioning that both of these problems are more than likely from bad storage and not the fault mentioned next. This showed up as corrupt background data.
After repairing both the burnt track with patch wire and the cut track with a small piece of wire bridging the damage I powered up the PCB to see what was next for me.
The game now runs but the main characters on the title and the sprites are all missing graphics, test mode revealed that whatever was wrong affected all text as well as the display was all garbage with a feint hint of order in the layout.
I suspected ram for this type of fault and given that IC33 was responsible for background data and that was OK I decided that the other custome IC84 was responsible for the sprites and text. Probing all the outputs revealed that one of the three ram chips IC74 IC75 or IC93 was problematic but as they are linked together it made it hard to pinpoint.
I decided the quickest way is to desolder them is one at a time since I have a desolder station and insert a known good swap.
As it turns out the last chip I swapped IC93 was the problem, its also worth noting that total failure of any of these ram chips will probably result in solid horizontal bars from top to bottom of the screen. I make a point of noting PCB behaviour when certain ICs are removed for future repair references.
Anyway after replacing the ram the game now works perfect and since I have never played it before gave it a bit of a bash... seems like a pretty good three player walk n bash game... it is after all an offshoot of double dragon which is my all time favourite game of this type only beaten by the almightly Final Fight.
2 days later... As it turns out the game started to get bad sound, it would play then not play then screech ect.... There is not much to the audio circuit and after playing it for ages a few days before I was pissed that there was still problems.
Anyway since the audio still play but is garbled I figure the CPU is OK and the Audio Amp ciruitry is OK (It was) which left the ROM and RAM, after some thought I concluded that since the problem was cold boot related it must not have been obvious in the first place as the PCB had warmed up a few nights back when repaired, It had the air con blowing on it and was COLD.... To test I booted cold and the problems were there, I then heated the RAM and the game would run sound no problems for ages, hit it with a blast of freeze spray and the problem returns.
Repeated test three times to be sure and for different time lengths and still the same, so I will have to hunt down some more ram. 2 Days later... Ram taken from a junker CPS-1 PCB (same rame used for Audio) and now audio is restored no mater what temperature.