3800 board "Door open C" problem

[Badbaud]

I was told this a 3800 board. This is an older GK machine and the MPU board has no surface mount chips and has a I/O tray above the MPU.

I got everything working except a constant "Door Open C". The game recognizes all other door open / close actions but the "C" door reports open and I can't find a "C" switch that would cause this. Also U71 (74HC240) on the board keeps blowing it's output pins 5 and 18 and shorting out the power supply (pulsing).

Any suggestions as to what could be causing this? Where can I get a schematic for this older system? I checked the downloads section and no mention of schematics for this older system were found.

Any help would be appreciated.

[Tilt]

Usually the C door is bypassed with a jumper. Here's what I have for schematics for the older 19in GK cabinets, the 13in cabinet is pretty much the same if that's what you're working with.  U71 is a SENET buffer, so it's probably something related to the I/O cards.  Pin 5 of U71 isn't connected to anything according to the schematics, so not sure what the deal there is. 

[Badbaud]

Thanks! Those diagrams should give me a fighting chance.

[Badbaud]

Usually the C door is bypassed with a jumper. Here's what I have for schematics for the older 19in GK cabinets, the 13in cabinet is pretty much the same if that's what you're working with.  U71 is a SENET buffer, so it's probably something related to the I/O cards.  Pin 5 of U71 isn't connected to anything according to the schematics, so not sure what the deal there is.

Where is the C switch normally located inside the machine?  What function does it relate to?

[Tilt]

In my 13" machine the harness is bundled up behind the bill validator and has a red jumper with a tag installed.  I believe the purpose for it is to run to the coin drop door (hopper overflow) in the stand so the machine alarms if the stand door is opened.  Here's a picture of mine and where's it's located on the schematic diagram.

[Badbaud]

Thanks, I'll take the pix to work and try to match it up. Stay tuned.

[Badbaud]

In my 13" machine the harness is bundled up behind the bill validator and has a red jumper with a tag installed.  I believe the purpose for it is to run to the coin drop door (hopper overflow) in the stand so the machine alarms if the stand door is opened.  Here's a picture of mine and where's it's located on the schematic diagram.

Found the jumper but didn't believe it was really making contact so I un-plugged the jumper and put it back in a couple of times and the "C" open error went away.

The games came up and it took bills but there were no buttons working or lighting up so I reinstalled U71 on the MPU board and swapped the I/O tray with a known good one.

Buttons and lights worked fine. This project is done. The customer has picked up the machine. Thanks for your help.

[Tilt]

My pleasure.  Glad you were able to get working again.