Recently, I picked up an ‘untested’ Twin Cobra PCB off of eBay. As most of us are aware, when something is advertised as ‘untested’, 9 times out of 10 its completely broken. This Twin Cobra was no exception to this rule.

 

Out of the box, the game booted up to a flat black screen, zero activity at all. When I see this on unknown condition boards, the first thing I do is give it a thorough visual inspection. I generally look for rust/corrosion, deep scrapes and gouges severing traces, physically damaged capacitors and IC’s, etc. Right off the bat, I noticed the the Koyo 28mhz crystal at X1 was hanging on by a thread! The other three had snapped off at the base of the crystal, so it was time to find a replacement. I was able to find a donor crystal in my parts boards.

 

I desoldered what was left of the original crystal, and then I installed the donor. The donor is slightly faster than the original, but it should be OK until a proper replacement arrives in the mail.

       

 

The rest of the board looked good – no gouges, no other damage so to speak. At this point when I powered it up, the game sprang to life!

 

Everything appeared to be working as expected, so I coined up and tried a game. Almost instantly, the next fault presented itself. Some (not all) of the sprite layers were incorrect. When the tanks aimed at towards 7:00, their turret would disappear completely. When larger tanks were destroyed, their remnants would take priority over my helicopter.

 

I knew something was at fault either with the ram or layer priority sections of the video board. From here, I started reading up on the mame driver, as well as the memory map for Twin Cobra posted on Toaplan.org. From what I could tell, it looks like sprite priority is controlled by the bipolar roms present on the TP-011 SUB (graphics) pcb.

 

I gave the 82S123’s a closer look, the bipolar rom marked B30-22 on the parts side of the PCB had a factory defect! There was a small solder bridge connecting pins 5 and 6. I fired up my soldering iron and removed the bridge.

 

Fired the board up, all faults were cleared! Game now works 100%. It’s mind-blowing to think that a game manufactured in 1987 has only played properly some 28 years later. This Toaplan masterpiece lives to fight another day! Until next time…

 

 

First of all, my apologies for the kilometric title but this seems be the correct one according to MAME which has emulated this game after my dumps 🙂

A friend of mine sent me this Battle Garegga bootleg PCB for a repair :

saying it had bad sound.Infact it was scratchy and noisy:

Besides, sometimes it muted completely.Regarding this last issue, I traced it to a bad YM2151 FM (actually a rebadged version marked ‘PD2001’) sound synthesis chip, once replaced it I got no more mutings.As for noisy sound, connecting the analog output (PIN12) of the YM3012 DAC (a ‘KA3002’ rebadged chip also here) to an external amplifier revealed that sound came out distorted.

Replaced it fixed the sound completely