PCB Repair Logs – Page 29

Teenage Mutant Hero Turtles repair log #6

PCB Repair Logs Comments Off

Apr 152018

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.

Black Tiger repair log #2

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Apr 142018

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

Xexex repair log #2

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Apr 132018

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:

Psychic 5 repair log #2

PCB Repair Logs, Repair Logs Comments Off

Apr 102018

My beloved original pcb developed once again problems after the last repair log you can read here:

Psychic 5 repair log #1

This time, the overall colour palette was pinked and all text was missing

After some troubleshooting I found again a problem with a Fujitsu ttl 74ls08, same type and week/year of manufacturing of the one I changed on the old repair log!

After changing it, the game worked fine for some minutes and then it developed a new problem

Game lost sync and became bluish

Again I decided to concentrate on the only Fujitsu 74ls08 ttls which were present on the board until I found the faulty one.

Same week/year of manufacturing and same fault: dead outputs

In addition, I found another couple of Fujitsu 74ls08 which had dead outputs and I decided to change all of them with good ones.

Now the game is 100% fixed but there are 3 more Fujitsu ttl waiting to be replaced. I ran out of parts otherwise I would have changed them immediately.

Dogyuun repair log #2

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Mar 212018

Got from Portugal another Dogyuun PCB (after the one of some months ago), this was declared as ‘dead’ by the owner :

And it was so.All I got was a steady black screen, no activity on board, no clock on 68000 main CPU.I checked voltages on edge connector and there was no +5V so the board was actually not powered :

A quick inspection revealed corrosion on edge connector:

Once cleaned it the board booted and played fine but sound samples were muffled and some static noise was present :

Some sign of electrolytic capacitor leaking was present on sound section :

I fired up my ESR meter and started measuring capacitors.A couple of them, the 220uF 16V @C7 and the 10uF 16V @C9, gave no reading so out of range of my meter (0-99 Ohm)

I replaced them, this restored clear sound.No other issue were found so board 100% fixed.

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