Demon Front single game PCB P1 BTN1 not working. Diagnostics and repair help request!

[Kujako]

So out of the blue, my Demon Front board stopped registering player one button one presses. Everything else works fine. Pulled the board out, and traced pin 22 on the JAMMA connector and couldn't find a fault. Inspection camera showed no breaks etc, but I had a hard time getting a reading from the pin to the resistors. Just for arguments sake, I ran a new trace from the pin to the resistor pack. Still nothing. Thinking it could be a bad resistor pack, but not sure what the expected readings on it would be (RSEC3). Any ideas or input would be appreciated.




Did some hunting around, and found this schematic of the RSEC3 resistor pack.

I measured the pack in question, and my measurements match. So seems that's not the issue. Not sure where to check next...

 

[Arthrimus]

You probably need to look past the resistor arrays. Trace out where P1B1 goes next and let us know what it is. I've never worked on PGM hardware so I'm not sure what to expect, but it's bound to end up in some sort of IC, possibly a custom. Check for cracked solder joints at that point.

 

[Kujako]

You probably need to look past the resistor arrays. Trace out where P1B1 goes next and let us know what it is. I've never worked on PGM hardware so I'm not sure what to expect, but it's bound to end up in some sort of IC, possibly a custom. Check for cracked solder joints at that point.

Yeah it seems like it runs to the IGS custom chip to the left of the sticker in my first photo. But not 100% sure. One issue is that due to the funky design of the resistor pack there are two pins effected. But I'll see if I can trace it...

OK... so I think I see it. I could be wrong, but the fourth pin down there looks like it may be on a lifted pad.

Update: So good news/bad news. I reflowed the area, and even more inputs stopped working. I'm calling this good news as it means I'm in the right area. I reflowed it again, and I'm back to having just the player one button one not working.

So... clearly it is the IGS 026a chip, but there's no information about it that I can find. So not sure which pin to look at.

 

[Kujako]

Fixed it!

Turns out, I'm just an idiot and when I did my first repair I ran the wire to the wrong pin on the resistor pack.

Thanks @Arthrimus for trying to help, but I fear this one is totally a PEBCAK error.

 

[GC8TECH]

You might find my website helpful, Plus there resistor packs for inputs arn't straight resistors.. there are Caps inside them as well. IF you need spare packs.. i do have parts boards here i could remove for you to help repair your board.

T.

 

[GC8TECH]

Here is the drawing of the resistor pack with the caps shown. I need to find my LCR meter to measure the caps values.

T.

 

[Kujako]

Here is the drawing of the resistor pack with the caps shown. I need to find my LCR meter to measure the caps values.

T.

Huh... seems like that would create a feedback loop without some diodes as well. Weird PCBs. So much of them has so little documentation available.

 

[GC8TECH]

Huh... seems like that would create a feedback loop without some diodes as well. Weird PCBs. So much of them has so little documentation available.

Have you checked out my new website?? Probably the best site for documentation on the PGM system and games.

 

[Arthrimus]

Huh... seems like that would create a feedback loop without some diodes as well. Weird PCBs. So much of them has so little documentation available.

I'm assuming that the capacitors in combination with the 330R resistors form a low pass filter for debouncing the inputs. The 10k resistors would be pullup resistors for the inputs.

 

[Kujako]

Have you checked out my new website?? Probably the best site for documentation on the PGM system and games.

I have not, but will do so.

 

[Kujako]

Board back in the cabinet with all the adapters (JAMMA to MVS, H/V adjustment board, JAMMA switcher board). All up and running again.