Received from USA this Psycho Soldier PCB:

It was labeled as ‘DEAD’:

And it was so, all I got was a steady black screen but this was not a suprise to me since the boardset (a three stack one) was fully populated by Fujitsu TTLs.First thing I checked was the presence of clock on CPUs, it was missing on both main and sub Z80 (but present on sound one)

I traced the signal from CPU board back to a 74LS367 @10A on bottom board:

Input pin 6 was properly receiving the 16MHz clock from the nearby oscillator but output pin 7 was floating:

As expected the TTL obviously failed the out-of-circuit testing:

Board sprang to life but colors were mostly incorrect and also sprites wrong and garbled during moviments :

I focused my troubleshooting on the bottom board as it contains sprites and background data and circuitry :

For first I checked the EPROMs, some of them were oxidized and corroded:

Afer some cleaning I dumped them, they were all good.So I fired up my logic comparator to test TTLs in circuit and found a couple of them with floating outputs (that’s the way Fujitsu TTLs are used to fail)

This restored the correct sprites :

But colors were still wrong.This was confirmed also in SERVICE mode, none of the them were correctly displayed:

The RGB lookup tables are stored in three 1k x 4-bit bipolar PROMs (Fujitsu MB7122 used here)

Probing the devices revealed that two address line were stuck high, I traced them back to a nearby 74LS174 @1M whose inputs were missing.These came from the outputs of a 75LS153 @1P-The TTL didn’t look very good with rust and corrosion on its pins:

The scope confirmed that both outputs had no valid voltage logic levels:

I pulled it:

Obviously it failed the out-of-circuit testing:

Colors were finally good and game played fine but I noticed there were some horizontal lines on left of the screen during scolling (see from seconds 25 of the below video)

At first glance I thought it was a fault but then I’ve been told by the owner and my friend Corrado that it’s actually a bug of the PCB.MAME Testers site confirmed it too:

https://mametesters.org/view.php?id=2910

I was about to close this repair when during testing suddenly the board failed again.Colors went bad again and lastly most of graphics disappeared:

The affected area was again the colors circuitry.The 74LS174 @1M which was previously tested as good showed floating outputs :

It failed when tested out-of-circuit:

At this point I took the chance to replace all other Fujitsu TTLs in this area :

Some passed the out-of-circuit test but two 74LS153 failed miserably:

Hard work always pays off and finally I could restore this board in all its glory (game was the first to use a fully digitized, full-length vocal sountrack)

Received from Portugal this Bucky O’ Hare PCB for repair:

Board was failing the POST all the time showing a ‘SOUND SYSTEM BAD’ message

The sound system was previoulsy reworked : the YM2151 was socketed

and the ‘054986A’ audio module had electrolytic capacitors replaced with thru-hole ones:

The solder side of the module showed signs of repairs too :

I suspected a broken trace underneath the module so I replaced it with a good one taken from a parts board.The error on POST changed to this :

I looked at the board and found that actually the device @C4 is the custom ‘054539’ while the one @C5 is 32k x 8-bit SRAM (whose data/address bus is connected to the custom)

Probing the RAM revealed that data lines were all stuck high:

Piggybacking it had no effect so most likely the ‘054539’ ASIC was bad.I removed it:

Soldered back a spare :

Board booted up fine and entered in game with no further issues.Another repair accomplished.

 

Received from USA this Wonder Boy PCB for repair, actually the board was a factory conversion on Sega System 1A hardware:

When powered it up I got most of times a steady black screen, rarely an ‘ERROR ROM 4’ message:

I fired up my Fluke 9010A to perform a ROM test.On some devices sometimes a valid signature was returned but more often I got error and a different signature :

There are six program ROMs:

When I dumped them my programmer complained about some bad contact:

It turned out legs of some EPROMs were dirty and oxidized.After polished them the board booted up but  clearly a color was missing (the RED one) and GFX faults were present :

Doing a visual inspection I found a couple of broken 1K bussed resistor networks :

After checked connections I figured out they were used as resistor ladder in the palette circuit.I replaced them, this restored the three RGB colors and showed better the grahics faults:

Backgrounds had wrong colors and some sprites (like main character) had missing parts and vertical lines through.As for first issue I went back to the color circuit where @IC151 lies a TMM2016 (8K x 8-bit) static RAM (whose data bits are routed to some 74LS175 flip-flop and finally converted to analog by the above mentioned resistor ladders)

Probing it revealed a unhealthy signal on an address line (A10 ,  pin 19), here’s a comparison with a good signal on the left:

Sure enough I removed the RAM :

Device failed the out-of-circuit testing:

Now the sprites issue.Relevant data is stored in four 27128 EPROMs installed on a small piggyback board:

Devices were dumped as good.After a quick check with my multimeter I found a missing connection between a data line of a ROM and the header which goes into the sockets :

I restored the connection and this fixed board completely.Another repair accomplished.