Jamma wiring question....Another ?, what am I missing ?

[mike boss]

FIRST OFF : Thanks for the info/tips guys. I've almost got my bartops completely wired.
I have another question, and for the life of me cant figure this out. I know its something simple,
my mind just draws a blank. I noticed that one of the jamma harnses was a little screwed up.
The test and service wires (as per standard jamma color) were on the wrong pin, as well as
the wires for the monitor. Blue was where red should be, red where blue should be, etc.

On the 1st 4 pins where the ground wires are I have all these extra connections. I cant figure out
what they are for. A ground wire is indeed going to the joysticks and buttons, the monitor has its ground,
yet I have all these extra connections. I cant think what they are for.

I've included some images. I got three harnesses from the same supplier, yet one of them did not have these extra wires.











Perhaps a stupid question, but I'd rather get some confirmation.
Providing I have no other use for a jamma harness over and above the existing cabinet it is in,
can I simply cut off the un-used wiring ? The harness is used in a bartop that only requires
1 player controls. Space inside the cabinet is minimal, and the extra wiring is taking up the space.
Any harm in simply cutting these off ?

I ask because I also have an existing keyboard encoder I got from Hong Kong.
Some of the wires pull double and  triple duty. For example one wire might be used for
P1 U/D/B1 & B2. I was hoping I could remove the un-needed wiring from the harness,
and use the wires for this application.



Thank you

[WhereEaglesDare]

why not just wind up the cables and then use a zip tie to keep them tight

why would you want to cut the harness up and fix it to where it can never be used again.

but if you want to you should be able to

[Ken Layton]

Common in the game industry is to coil up the unused wires with a wire tie. You never know what wires you might need in the future and it's nice to have them already there.

[RayB]

I'm also in favour of keeping the wires, but I understand that some harnesses have really long wires, so a coil of wire might take too much room in a small bar-top.

Also, a bar-top has no room for 2 players right? So in that case I'd say cut off all the 2nd player wiring, keep the remaining loose wires as short as possible but still long enough for future use, and then coil/tuck away those.

[mike boss]

With the harnesses so inexpensive I figure should I need one again, I'd just buy it new.
Ray B - correct, no player 2 in the bartop. I actually like the idea of simply cutting off any/all wires associated with player two.
I think that would work best, and make a lil extra space.

[M.Lanza]

I just push the unused pins with the wires still attached out
of the jamma connector with a small screwdriver.

It ends up looking neater that way and I can add the wires
back into that, or possibly another jamma connector if I want
to add controls or something later on.

[Kevin Mullins]

I just push the unused pins with the wires still attached out
of the jamma connector with a small screwdriver.

+1
If you are going to remove them, why not remove them properly so that they can be re-used elsewhere at a later date?
I don't know how many times I have wired up a JAMMA harness for a game that needed say a fourth button or something, like a Neo Geo for example. (JAMMA slots 25,26,C,D)
If you buy a new "standard" harness, those slots will be empty.
Or just in case you screw something up somehow and need to replace a wire, much easier if you have some spares laying around ready to go with connectors already on them and such.

My $.02 

[mike boss]

What am I missing? (see above)

[BobA]

"I ask because I also have an existing keyboard encoder I got from Hong Kong.
Some of the wires pull double and  triple duty. For example one wire might be used for
P1 U/D/B1 & B2. I was hoping I could remove the un-needed wiring from the harness,
and use the wires for this application."

It sounds like your encoder is multiplexing some of the buttons so you have to use the proper ground to get them to work.  You cannot use the common grounds in a jamma harness if the encoder has multiplexed buttons.

[mike boss]

The encoder I showed to a friend who was an electrical engineer in his home country.
He was able to help me out, and as I thought it was OK to have the wires preform double and triple duty.
No function would share the exact two wires, making each function unique.
I'm yet to test the encoder but "fingres crossed" think it will work flawlessly.
It's no iPac, but it also wasn't the $66 I paid for an iPac.

I'm just confused as to what all these extra black wires are for.
The last four pins of the harness are grounds and run to the joysticks and buttons.
A wire is bridged from the last 4 pins to the first 4 pins, and a wire traces back to the monitor.
Everything appears to have the propper ground.
So why the extra wires, what am I missing ?

[MonMotha]

JAMMA uses a "common ground" approach which is incompatible with the matrix arrangement the encoder you have seems to use.  If you could post a wiring diagram for how your encoder is supposed to be wired (should be provided by the manufacturer), that would help.

More info:

On JAMMA, the first and last 2 rows of contacts are "cabinet ground".  Where exactly they all run is somewhat ill defined.  On many cabinets, the ones at the lower numbered positions (near the other power wires) run back to the power supply as power common, and the high numbered positions (near the joystick and button wires) are used as the common lines for the switch inputs on the buttons and joysticks, but some cabinets wire it other ways.  Midway, for example, tended to put 2 wires from the power supply on positions 1/A and all the way down on 28/FF, using 27/EE for control common and 2/BB to daisy chain power common to other things in the cabinet.

Since the function of each individual "ground" position is not defined, it's also somewhat common for the cabinet side to connect them all together.  Most arcade PCBs do this on the PCB, anyway.  Since the "ground" line for each individual switch is not available, you can't use JAMMA with a matrix configuration that requires a defined pair of wires to be used for each switch.  It can only be used with a true dedicated input/common ground encoder.

The "ground" wire running to the monitor is "video ground".  To help keep out interference patterns, there is a dedicated pin for this on JAMMA (14).  It should not be connected to any other "ground" via external wiring.  The arcade PCB will connect it properly for you, or you should connect it to your video card's "ground" lines if you're using a PC with a breakout cable.

[mike boss]

Thank you once again for all the info.
I should clear something up.
My issues with the encoder have been solved.
Some of the wires do pull double and triple duty.
However no connection will use the exat two wires.
So each combination of two wires will preform a
unique function.
Thanks again.

My new question is with respects to a JAMMA harness
and standard wiring. To me it appears the harness
has extra wiring, and I cant for the life of me
figure out the placement.

Pins 1 & 2 (including both top and bottom row) go to
the power supply. There is a wire that goes from pins
1 & 2 and is bridged over (better term ?) to the last
two pins on the harness. The last two pins got the
joysticks and buttons, and have a dasiy chain attatched.
Also from the last two pins a wire is again bridged and
run to the monitor connection (as the monitor ground).

Now this basic set up seems to be standard on all the
harnesses I have. And as far as I can tell (remember)
that is all that needs to be grounded. Yet from the
first two pins on the harness several other connections
are attached. They are the images posted above.
I can't for the life of me think of me think what they
are for. One connection (as shown) is a partial daisy
chain with two connections. Any help would be great.

Thanks