I got this game for a repair:
The game had some background problems ( unfortunately I forgot to take a pic ) and a sprite problem:
The background problem was fixed reflushing the custom chip 56.
As for the sprite problem, after some time checking the part of the circuit responsible for the sprites, I found a couple of 6116 sram @D5 and D6.
One of them had some weak signals on the data lines and tested out of circuit it was confirmed as bad
After replacing the sram the game was fixed
I’ve been sent from Ireland this R-Type II PCB for repair, actually a conversion on Major Title (Irem M82 hardware)
Board played fine but sound was completely absent:
Here is an overview of the sound circuit:
Someone previoulsy tried to fix the lack of sound by replacing many components.The analog part of the circuit was doing his job as putting my fingers on solder side of the amp produced some noise.Probing the Z80 sound CPU revealed /INT line was stuck LOW.While testing components something strange happened, I got sound fully working :
The IC I was testing with a logic comparator is a 74LS244 @IC13 whose ouptuts are tied to the 8-bit data BUS of the Z80/RAM/ROM/YM2151.Signals didn’t look fine to me:
But when I put the clip of my logic comparator on the TTL they correctly toggled :
Data lines are tristate, this means they can be in high-impedance state (Hi-Z) in addition to the 0 and 1 logic levels.When outputs are tri-stated, their influence on the rest of the circuit is removed, and the circuit node will be “floating” if no other circuit element determines its state. Usually pull-up or pull-down resistors are used to influence the circuit when the output is tri-stated.This even more when a same line is shared among different devices like in my case.The 8-bit data BUS of the sound circuit is pulled-up by a 10K resistor array:
When I went to measure it I got high resistance on half of its pins :
I pushed the array a little and this happened :
It was actually cracked in a not visible way (this explains why the logic comparator fixed the issue, it acted like a pull-up).I replaced it:
This restored the sound, board 100% fixed
Received a box of faulty PCBs to repair from USA.I started my work on them with this Teenage Mutant Hero Turtles by Konami:
PCB was in very good state and played fine with correct sound too but it had a color issue, the screen was yellowish simptom that the BLUE color was missing:
BLUE, as well as RED and GREEN, is generated by a custom SIL marked ‘052535’ (basically an R2R resistor ladder which acts as DAC , see my reproduction post here for more details)
Probing the custom revealed activity on all inputs (pin 2-3-4-5-6-7 ) but output pin 8 was stuck low:
So the component was internally faulty.I replaced it with same part taken from a spare board :
This restored the missing color.End of job.
Got a Black Tiger for a repair which had a colour problem on some graphics
It lacked some shades of colour
I decided to look around the palette rams @6C and 6D until I found a fixed address line
Tracing back I found an 74ls157 @5D with an output stuck low.
After checking the inputs I found one of them stuck low and according to its truth table, the output is always low.
Tracing back I found a 74ls273 witth Q3 output low and D3 input oscillating.
Piggybacking a good one restored the correct colours.
After changing it , the game was completely fixed
Received from France this mint Xexex PCB:
The board was bought from Japan as working but when arrived there was a noticeable sound issue, a loud buzzing noise present also at lowest volume level :
Obviously the culprit was the ‘054544’ audio module.Electrolytic capacitors on it were already replaced but this was not enough :
Most likely the probem was on the underneath of the module so I removed it and installed sockets:
There was some corrosion on underneath but nothing really serious:
I decided to test the module on an X-Men PCB and it worked fine, audio was clean:
The technical reason why it worked is that X-Men doesn’t use the pre-amplification circuit of the module (a LM358 OP-AMP is present externally on PCB) while Xexex does.So the problem was the 4558 OP-AMP on underneath of the module.I removed it and replaced with an LM358:
The buzzing noise was cut out:
Lastly I painted the module to finish the job:
