Midway Gun Fight

billyseven

Active member
Joined
Apr 29, 2006
Messages
284
Reaction score
65
Location
Mounds View, Minnesota
I've been working on a Midway Gun Fight where one of the cowboy's guns couldn't be aimed downward and the other gun worked intermittently.

It turns out that the 18 pin Molex connector was to blame for the intermittent aiming and some other problems with movement too.

Regarding the second gun problem I had to replace the H2 optocoupler and now the game works correctly but this chip gets pretty warm and the resistor network GH12 used for the H2 chip gets hot enough to burn you.

Due to the design of the games controls these gun inputs are always grounded unless one of the guns is moved to a different position. My board and some others pictured on the internet seem to have a minor black discoloration above this chip suggesting they may all get hot. Also If I pull H2 out of the circuit or even just bend up pins 2 and 3 nothing will even get warm. I have checked all of the wiring on the control panel and harness, both visually and with a meter but I don't see any problems.

I'm wondering if anyone else has noticed if their game board gets overly hot at this location as well?

One thing to note is that someone had already made a custom discrete resistor network for GH12 but since they had used a different value for the resistors then what is shown in the schematic I chose to replace them with the correct SIP resistor.

Thanks in advance for any thoughts or input!
Dave
 
I'm investigating exactly this symptom right now as I had someone send me a couple Gunfight boards to fix, one of which is missing the resistor pack at EF12 and I can clearly see on a different board its pretty baked. Both of these have custom resistor packs at GH12 which I'm starting to think is a factory mod.

Depending on what Opto you used for H2, if you used a ILD opto you may want to replace it with a MCT6 as it looks like they use a third of the current the older ones do, In addition I'd put back the custom as the sip resistor pack may be very low wattage compared to what it should be - the one I'm looking at here looks like it has 1/2watt resistors.

It may also have to do with the fact that the voltage going to those resistor packs is not regulated - power supply variations may mean some are fine and others are baking to death.
 
Thank you for sharing, this is most excellent info!

The repair looked relatively professional but yet I've seen enough "field repairs" to make me question it without any additional supporting information. The few photos I found on the internet only showed SIP's in all locations and there doesn't seem to be any service information out there regarding this possible issue.

I also appreciate the MCT6 suggestion since I'm pretty sure I used ILD's for this repair.

Thanks again!
 
I figured out why GH12 fries!

Look at the top left corner of the schematics...it runs 2 optos (4 leds total) off two legs! Cheaters! Each led should have its own resistor!

In reality it should be a bigger resistor pack with seperate resistors feeding each opto or at the minimum use 1 watt resistors.
 
Back
Top Bottom