Jamma Extension Harness Mod Write-Up

zenomorp

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Hey guys. I know there are a lot of us here that use/need the Jamma extension harnesses and from what I can tell, they are all the same. I have purchased a few from all different suppliers and I always get the same ones. There are a few issues with them. They will not work for most games right out of the box because there is no video ground on pin 15 of the component side of the connector as well as the 5v, 12v, and grounds missing from the same side....

Before2.jpg


So you have to solder a wire onto the ground wire at pin 28 of the solder side and jumper it over to pin 15 of the component side to provide a ground for the video as well as jumpering the 5, 12, -5, and grounds from the solder side over to the component side because they are only on the solder side of the connector...

Solder side...

SAM_0433.jpg


Component side...

SAM_0428.jpg


There's also no -5v. If you are going to use this extension harness for any of the 90's Midway fighters or any game that needs the -5v, you have to install a jumper from the Jamma connector to the edge connector at the appropriate locations...

Before1.jpg


After1.jpg


Hope that makes sense because if you don't do thee mods, your board MIGHT work, but your colors will be wrong because of the missing video ground and your audio might not work because of the missing -5v. Let me know if you have any other questions and opinions are appreciated!

Thanks!

:)
 
What suppliers have sent you this cheap harness? I, personally, hate the solder tab harnesses, I have seen them break too often to trust them. Add to that the fact that so much is missing from this harness it just doesn't seem like something worth buying...
 
What suppliers have sent you this cheap harness? I, personally, hate the solder tab harnesses, I have seen them break too often to trust them. Add to that the fact that so much is missing from this harness it just doesn't seem like something worth buying...

I got them from TwistedQuarter, but it's not really their fault. I've bought these from Jammaboards and a few others and they are always the same. I've NEVER purchased one that DIDN'T need to be modded like above. Not saying they don't exist, just saying I've never come across one.
 
I build my own with the parts I prefer or I buy them from Bob Roberts if I am in a hurry. These must be the cheap Chinese ones available for a couple of dollars.
 
I build my own with the parts I prefer or I buy them from Bob Roberts if I am in a hurry. These must be the cheap Chinese ones available for a couple of dollars.

same, I've got a ton of spare harnesses, just needed to pick up some nice thru hole boards
 
That is near the worst new harness I have seen. One wire for +5 and one for GND, wth?

I know your mod get's the harness working and the information you provided is very useful, but I wouldn't suggest doing it that way. You need to add a wire from the jamma plug to the PCB. One wire carrying all of +5 and GND will eventually result in something getting burnt. You might get away with it on the low powered multi boards.
 
I just make my own. It takes about 1 1/2 to two hours to do and it looks kind of goofy in the middle but what I do is take two jamma harnesses that are fully stuffed, lay them on a long table across from each other end to end and strip the ends of each wire on both harnesses with my wire stripper and then tie them together -- A to 1, B to 2, C to 3, etc.

I've done it a few times with no problems (except my first attempt when I put A to A and 1 to 1).

I use duct tape as I tie them together individually and finally a couple of strong rubber bands in the middle to fold it over.

It takes a couple hours but, if you use two harness that are four feet each, you end up with an eight foot harness.
 
That is near the worst new harness I have seen. One wire for +5 and one for GND, wth?

I know your mod get's the harness working and the information you provided is very useful, but I wouldn't suggest doing it that way. You need to add a wire from the jamma plug to the PCB. One wire carrying all of +5 and GND will eventually result in something getting burnt. You might get away with it on the low powered multi boards.

Makes sense and you are probably right. The mods I did and describe will at least get the person going as they are pretty much useless when you get them. That's a good point.
 
Makes sense and you are probably right. The mods I did and describe will at least get the person going as they are pretty much useless when you get them. That's a good point.

Also, just to be clear I didn't meant to say your harness was crap, just the original one for not having all that stuff already done.
 
These must be the cheap Chinese ones available for a couple of dollars.

OZ is right. I got a JAMMA harness from someone who gets them from China on the cheap and it was the same thing. Try popping a wire out and look at the cheap pins they use. Pretty much just a flat piece folded over, no structural strength built in at all. I wouldn't be surprised if the pins stop making contact with the edge connector after a fairly short time.

The one I had was so bad I just cut the wires off to reuse and tossed the rest. I don't think the money saved is worth the potential trouble a bad harness can cause.
 
That is pretty much what my builds look like. I can't tell by the pics but I assume it is populated in all necessary areas.

If I buy another and not build it myself it will be this one from Bob:

jammaext.gif


Honestly, I will probably just buy a JAMMA Harness off Bob and combine it with a JB-1 Fingerboard.

The main reason is because I hate buying the wire, I don't mind soldering.
 
If I buy another and not build it myself it will be this one from Bob:

jammaext.gif


Honestly, I will probably just buy a JAMMA Harness off Bob and combine it with a JB-1 Fingerboard.

The main reason is because I hate buying the wire, I don't mind soldering.

get me a few of those fingerboards and i'll give you a harness. hell get a bunch of them and i'll make you one.
 
If I buy another and not build it myself it will be this one from Bob:

jammaext.gif


Honestly, I will probably just buy a JAMMA Harness off Bob and combine it with a JB-1 Fingerboard.

The main reason is because I hate buying the wire, I don't mind soldering.

How much does that one run? I bought one of the cheap ones, so I am guessing it will have to be modded to work with a 1315 in 1 board, correct?
 
How much does that one run? I bought one of the cheap ones, so I am guessing it will have to be modded to work with a 1315 in 1 board, correct?

Most likely. That thing definitely will draw a few amps so adding some extra power wires from the Jamma end to the finger board will probably be a wise move as well.
 
great writeup, but jamma spec says video ground is on pin 14
 
great writeup, but jamma spec says video ground is on pin 14

Thanks. Yes, but the grounds are technically all the same. As long as the video ground is going to a ground, whether it's on pin 14 or not, it will still work. I know you are saying that the video ground is supposed to be on pin 14, but it will still function as advertised as long as it's grounded.
 
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