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.
PCB Repair Logs, ReproductionsComments Off on Teenage Mutant Hero Turtles repair log #5 and Konami ‘007340’ reproduction
Mar182018
Got in a trade this untested Teenage Mutant Hero Turtles PCB:
At first test the board turned out to be faulty.Sprites were scrambled and some sound samples scratchy:
I launched a MASK ROM test which reported as bad all four 4Mbit devices storing sprites data:
Obviously the result didn’t mean the MASK ROMs were all bad, this was quite unlikely but for sure there was a problem in the sprites generation circuit.
Most of the circuit is condensed in two ASICs, the ‘051960’ which generates the address for the MASK ROMs and the ‘051937’ which reads their data:
Judging from type of fault, the ‘051960’ was generating wrong address, you can see its implementation in this snippet of schematics :
Also scope analyzing confirmed my suspicions :
This lead me to remove and replace the ASIC:
This restored sprites so the IC was really bad (it’s not the first time, see my past repair log of Block Hole)
Now the sound issue.A quick visual inspection revealed that one of the two components marked ‘007340’ was cracked in two:
As schematics suggest the ‘007340’ is a resistor ladder (R2R) used to convert into analog the digital bits outputted from the ‘007232’ PCM controller so I made a very rough replacement that worked fine:
Later I properly reproduced it :
Another PCB fixed and another (little) custom reproduced.
Most likely the component was internally faulty so I replaced it with a repro of mine:
Finally the board booted into game but the sound was barely audible also at maximum volume level:
After a visual inspection I found that the component silkscreened ‘PX4460’ was missing from sound section:
Board uses also another little sound custom, the “LPF6K”, here is a picture from another board for better understanding:
Actually you can replace them by installing the parts they are internally made of directly on PCB (there is silkscreening for them) but I wanted to keep the all-in-one solution the so I decided to have a look inside them in order to reproduce both (although the ‘LPF6K’ was not missing on my board).I removed the coating and did an Hi-Res scan;
On the left on the above picture it’s the naked ‘PX4460’ which, like its name suggests, embeds all the parts (minus the 1000uF 16V electrolytic capacitor, this is on the PCB) needed by the typical application circuit of the ‘LA4460’ amplifier as datasheet shows :
On the right of the scan, it’s the ‘LPF6K’ that contains an LM324 OP-AMP and all its required parts, its function is to pre-amplify the sound.
Given the simplicity of both customs it took few time to figure out schematics and route them to a replacement PCB.Here is the result:
Installed on PCB ready for the smoke test:
Success!Sound was restored and both repro worked fine as replacement.
