Another PCB from Olly. Not sure if this is a bootleg or not but it is certainly of lesser quality than the other Double Dragon boards I’ve had.
Anyway, on boot up we get this mess but at least it boots

I pulled all the ROM’s on the video board to start with and found the 4 tile ROM’s dead.

I replaced these with 27C512 EEPROM’s which then gave me this

Much better but all the sprites are missing.
Looking at the schematics I could follow them through testing from the ROM’s onwards.

I ended up at a 7425 where all the inputs were active but the output on pin 8 was dead

I replaced this and tested again. All the sprites were back on the title screen but the in game sprites had coloured blocks around them.

Seeing as though I had 4 dead ROM’s I decided it wasn’t too ridiculous a thought to think that some of sprite ROM’s were dead too.
After confirming that the sprite ROM’s were being selected correctly I pulled them all and checked them.
I found 1 dead ROM here

Again I replaced it and tested

All graphics now fixed, the sound however was a different story.

The sound effects were all messed up but I could hear the music was fine in the background.
I pulled the two PCM ROM’s and tested them. Both failed.
Replaced these too and tested

All fixed.
7 dead ROM’s and 1 TTL. Not sure whether the ROM’s are just getting too old now or if they were taken out by a voltage problem.

Received from Austria this Heavy Barrel PCB, a run and gun arcade game released by Data East in 1987 :

Board was in really good shape and game was fully playable too but lacked of sound :

Using an audio probe revealed no sound came out from analog circuit hence the fault was of digital nature.Audio system is ruled by a 6502 CPU located on top board :

Its pinout :

Checking it with a logic probe revealed that the /NMI line (pin 6) was asserted as well as two address lines were stuck low (A12 and A14)

A non-maskable interrupt triggered is usually due to some hardware failure hence for first I dumped the ROM containing the audio code (located on bottom board), it turned out to be good.Then I focused on the RAM accessed by the 6502, a 8K x 8-bit device (6116 compatible)

As soon as I piggybacked it with a good chip I got some random sounds played.The scope revealed weak signals on some data lines of the RAM (a good signal on the left of below picture for comparison)

I removed the IC :

And sure enough, it failed the out-of-circuit testing :

New chip fitted :

Sound was thus restored and another board fixed.

Got for repair this original Rapid Hero PCB, an obscure vertical shoot ’em up released by NMK in 1994 and a very sought-after board :

The board booted up but some sprites were affected by jailbars :

Besides, an entire music track was missing or sometimes corrupted as well as some sound effects:

 

The board had some sign of previous repair on solder side :

This is the area of the ‘CN1’ and ‘CN2’ connectors where the ROM board, which contains all the game code and data, plugs into the mainboard:

The repairs let assume a weakness and subsequent failure of the headers connections probably due to repeated disconnections and insertions of the ROM board.So I checked with a multimeter in continuity mode all the traces from the ‘CN1’ header and found another broken one that I promptly patched :

This fixed the graphics, no more jailbars on sprites :

Now the sound issue.

The audio circuit was previousy reworked, one of the OKI MSM6295 was likely replaced and one trace was repaired but this was not the culprit :

I noticed that if I pressed the ROM board on the ‘CN2’ connector some of the missing sounds were restored.I checked traces from ‘CN2’ to mainboard and found two missing connections to the ‘NMK112’ custom ASIC (responsible of  bankswitching the sample ROMs of the two OKI6295 ADPCM chips)

I patched the traces with some AWG30 wire:

Sound was totally restored and board 100% fixed.Repair accomplished.