Oct 152019

Got K1ngarth3r’s Mega-Tech PCB here.

On these boards there is a daughterboard present which houses the Z80 used for the menu.

This daughterboard is used for book keeping and isn’t really required so to save space I fitted the Z80 directly into the slot the daughterboard previously occupied.

The fault was the board didn’t see slots 4, 6 or 7 as shown in the picture he sent

Initial inspection showed the EPROM for the menu was fitted upside down but it wasn’t dead and the menu wouldn’t work at all if this were the actual fault.

Using the partial schematics I made a few years ago I could quickly pinpoint an area to start checking from.

Using my latest favorite tool, Slice, I could easily see that for some reason the 3 aforementioned cartridge slots were never being addressed.

This is a bit weird as on initial look at the disassembled code it seemed that it just counted through the slots.
A bit more code scrutinizing revealed that the CXD1095 chips are read back between slot addressing.
Using the Fluke 9010 I could now see that at certain output configuration on the CXD1095’s would lock up the chip and skip whatever it was doing.
I wasn’t really surprised at this because every single Mega-Tech PCB I’ve looked at has had issues with these chips.
I ordered a couple of these chips up and waited….. and waited……… and waited until I got hit with a lovely little letter from Royal Mail telling me I owed them money for customs fee’s.
I paid this and a couple of days later I received my items.
I removed the old and fitted the new

Pleased to say this board is now working again

 Posted by at 8:40 pm

Double Dragon repair log #10

 PCB Repair Logs  Comments Off on Double Dragon repair log #10
Sep 292019

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.

 Posted by at 5:42 pm

Xexex repair log #3

 PCB Repair Logs  Comments Off on Xexex repair log #3
Sep 222019

Got this board from Olly.

Board looks very clean and plays but has graphical issues

Initial visual inspection showed nothing. All voltages seemed fine too.
Next I started gently pressing down on the custom chips which made a lot of changes when I pressed on 053250

Found a bunch of pins on that were lifted.
I reflowed these and checked the rest of the chip which all seemed fine.
Next boot up test gave me a lot better results but there were jailbars down the whole screen sometimes.

Continuing pressing the custom chips I could make everything change again by pressing on custom 054157.

Found most of this row lifted

and few a few here

Reflowed those little guys and all is fixed in Xexex land.
Its a really nice game that I’ve never played before.

 Posted by at 4:40 pm
Sep 212019

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.

 Posted by at 10:31 pm

Rapid Hero repair log

 PCB Repair Logs  Comments Off on Rapid Hero repair log
Aug 292019

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.



 Posted by at 10:57 am