Spy Hunter TECH - Guns Stuck on - Anyone know how to fix this?

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Spy Hunter TECH - Guns Stuck on - Anyone know how to fix this?

Was playing Spy Hunter. All works well. All of a sudden, the machine guns are stuck on and I'm not depressing the trigger. I re-seated everything and still they are stuck on. Swapped boards to rule out the trigger button. It's definitely a board problem. Anyone know which chip controls the guns and which board? Seems like some IC is stuck on. Or, could this be a flaky interconnect cable? Hope someone could assist.
 
Send the board to cdjump for repair? Probably the cheapest and maybe quickest way. :)

Does your shifter still work?

I looked over the schematics and traced the machine gun signal. It comes into pin 15 on connecter J4 on the super sound I/O board (http://www.arcade-museum.com/manuals-videogames/S/SpyHunterSchematicsPg1-2.pdf). J4-15 feeds into pin 13 on a 74LS244 at E2 (http://www.arcade-museum.com/manuals-videogames/S/SpyHunterSchematicsPg5-6.pdf).

If pin 7 on E2 and pin 7 on F2 are tied together (check for continuity) and your shifter still works, the problem is most likely the 74LS244 @ E2. It could also be the resistor or cap tied to pin 13 on E2 (C115 and RM4).
 
switch

Have you actually taken apart the controls and disconnected the trigger microswitch button? I recently replaced the buttons on my machine, the triggers are Cherry e33-00k parts.
 
Anyone know which chip controls the guns and which board? Seems like some IC is stuck on.

Looks to me like E2 on the Super Sound I/O Board. Machine gun button appear to go to pin 13 of that 74LS244.
 
i vote either the 244 or a bad interconnect cable. Without looking through the schems, the one referenced above sounds right. I had one that had a similar problem, but it was coin 2 that was stuck on.

edit - it was the 74ls244 that was bad, btw. I've also seen that stupid cap cause the same issue.
 
Update on repair

O.K.. Now I'm a bit stumped! I changed out E2 (74LS244N). No change.. Gun continues to fire on it's own. I then figured what the hell, change out CP15 Capacitor. Still same problem. Now moving on to RM4 (series of resistors). Changed this out.... Still have constant guns.

I can rule out the ribbon cables. I swapped the Super Sound I/O with another one from another board stack. The game works fine. This symptom is definitely limited to the Super Sound I/O board. There is another capacitor and resistor just before the RM4 series resistor. I'm going to swap these out tonight and will report back. Very strange. I changed all the suspected parts and still it's an issue. Any other ideas while I"m swapping parts tonight?
 
Check the voltage on pin 13 of E2. With the gun is stuck on, it should be low (at or near 0VDC).

Yep, the a short cap (C115) could pull the line down and cause continuous firing. I suppose it's also possible that the pull-up resistor (part of the RM4 resistor pack) isn't making connection and thus isn't pulling the line high.

If it's neither of those, and replacing E2 didn't fix it... perhaps there's a shorted trace somewhere? I don't really see how it could be upstream, as on the other side of the LS244 is a data bus... if it were jacked over there, I'd think you'd have more problems than just the machine gun.
 
Fixed!!!!!!!!!!!!

Cap at position C115 was shorted. I took it out of circuit and the guns fire normally as they should. Thanks for the help. This is one to document for the records. Can't believe C115 pulled the guns to keep them on.

CDJump and Darren you were both correct on this one. Can I keep this cap out of circuit? Is it necessary?
 
Caps

If your SH PCB has the original caps I would recommend replacing all of them. Most of the caps can be bought on ebay quite cheap.
 
Replaced Cap

I replaced C115. That was the culprit. I have a spare trashed sound board. It's great for pulling parts off of so I took a cap from it and put it right in. Works great now..
 
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