Strange problem with Heavy Barrel pcb - Need Help

[rolins]

I have a weird problem on my Heavy Barrel pcb. The 2nd button on Player1 side is being held down for some reason. So when I go to the diagnostic screen, the 2nd button is constantly registered as 1 when it should be 0 because I'm not pressing it. Its definitely the pcb that's at fault here since I've tried it on 2 different superguns. I've tried cleaning the jamma edge and reseated some roms but that's about it. I'm not very tech savvy when comes to troubleshooting pcbs. I can use Player2 side without problems, but when my friends come over I want some co-op play. What do think I should try? Any help is appreciated.

[rolins]

   Anyone at least have a schematic for the DE-0297-0 pcb? This is the top board of my Heavy Barrel game. I'm having a difficult time tracing jamma pin23 (player1 button 2) since it goes underneath all kinds of components. Not to mention I think Pin23 is bridged to the common GND, so doing a continuity test doesn't work well unless I'm tracing it with my eye.

[Kevin Mullins]

Well, if pin 23 appears to be physically bridged to ground then that would cause it to stay on. (or do you mean a continuity check shows it goes to ground?)

[rolins]

Well, if pin 23 appears to be physically bridged to ground then that would cause it to stay on. (or do you mean a continuity check shows it goes to ground?)

Both really. I used a multimeter on the jamma connector, and definitely pin23 and GND are connected.

Heavy Barrel is a 2 layer pcb. The bottom pcb containing the game, and top pcb has the main CPU and jamma connector. The top board is model DE-0297-0 and I believe it's the culprit because even when I separate it from the bottom pcb, pin23 and GND is still bridged.

[Kevin Mullins]

I know it's probably a pain to trace, but I'd bet there's a simple TTL chip right close to the area of the edge harness that pin 23 leads to. That chip is most likely shorted.
I don't have one to look at to be of much more help without either the board or a decent schematic.

[rolins]

How can I tell if a TTL chip is shorted? Is measuring with a volt meter enough?

[Kevin Mullins]

I use a multimeter with continuity check.....

RED lead on ground.
Black lead for probing around chips.

Any chip leg that comes up as a dead short needs to be traced to see if it is physically tied to ground.
If it is NOT tied directly to ground somewhere.....it's probably bad.

Start with the first chip pin 23 leads to.

My $.02

[rolins]

Kevin thanks for all the help, I made some progress. Today I found a bad component at location NF6. The part# MTX222MB...not sure what its for but it leads directly to Pin23. I hope this is the only part that's bad. Now I just need to find a supplier I have feeling this going to be tough to find. As last resort I may have to salvage it from another broken Data East pcb.

[channelmaniac]

It's a small coil inside a package.

Desolder it from the board and see if the short to ground goes away on BOTH pins you desolder.

If one of the pins is shorted to ground then you still have to follow the trace back to find where the short is.

[Kevin Mullins]

I was just looking at my Captain America board and it uses the same exact ones.
The two outside pins will show like a short, but between the middle and either outside pin should not. Verify it against other on the board that are known working.

I noticed on mine that EVERY pin coming off the JAMMA harness has one in place, even though this particular game doesn't actually use them all. (i.e. it's only a two button game)
So if the Heavy Barrel pcb is the same situation, there may actually be an "extra" one on your board already if you truly find out that component is bad you can swap them.

[rolins]

It's a small coil inside a package.

Desolder it from the board and see if the short to ground goes away on BOTH pins you desolder.

If one of the pins is shorted to ground then you still have to follow the trace back to find where the short is.

I had a difficult time desoldering. I just tried removing the bad MTX222MB part and in the end I snapped the legs right off the board from frustration. The pcb absorbs heat like nothing I've encountered. :/ Is it because my 15w soldering iron doesn't generate enough heat?

I did find another bad component at location RA30 which also leads to Pin23. Not sure on the part# but it has RCDM-I1 written on it.

The last picture shows a burnt mark behind one of them. This particular one must be cause of it b/c it's shorted to ground.

I was just looking at my Captain America board and it uses the same exact ones.
The two outside pins will show like a short, but between the middle and either outside pin should not. Verify it against other on the board that are known working.

I noticed on mine that EVERY pin coming off the JAMMA harness has one in place, even though this particular game doesn't actually use them all. (i.e. it's only a two button game)
So if the Heavy Barrel pcb is the same situation, there may actually be an "extra" one on your board already if you truly find out that component is bad you can swap them.

Great idea! The parts meant for the 3rd buttons are still good.

[Kevin Mullins]

I meant to warn ya about soldering on those Data East boards, I've messed up a few traces on mine trying to remove components. They have through holes, which means the solder will attach itself to both the top and bottom of the board. Recommend using a dab of flux and solder wick or a heated solder sucker. But you don't want to apply toooo much heat as the traces on these board seem very delicate, more so than any other I've messed with.
If ya start to get frustrated..... back away from it. (trust me) 

That red component is a resistor pack, never seen one of those burn like that, especially for control inputs. I would continue tracing and find out where it leads to from that resistor pack trace.

My Captain America inputs seem to lead back to a fancy surface mount chip, hopefully yours doesn't. I don't have any other Data East boards to look at and compare to yours.

Still really surprised that only ONE input has been effected on yours.
 
Wish the schematics in the manual for yours were a bit better.....drawn the way they are makes it harder to figure out without printing the whole dang thing off to bounce from page to page. (for me anyways)
http://arcarc.xmission.com/PDF_Arcade_Manuals_and_Schematics/Heavy%20Barrel.pdf