Questions on modifying a Jamma harness

dukesilverfan

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I have several questions in regards to this Chinese Jamma harness I bought. I want to make it work for a supergun/test rig I am doing, so first the questions, then the pictures of it. Let me know if I can clarify at all:

1. What is the best way to add wires to the pins, simply solder directly to the pins and then shrink wrap? I want to add in -5V for my Midway games.

2. The video ground is missing on this harness, should I add that, or can I just use another ground? The video connector from this harness is currently connected to pin A on the Jamma connector.

3. What should I do for pins e, f, 27, 28. I know they are marked as grounds, but they are currently not on my harness. Do I need those? If so, do they ground to anything specific, or just loop back to the power supply ground?

I hope that all makes sense. Attached are the pictures from my harness:
 

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I have several questions in regards to this Chinese Jamma harness I bought. I want to make it work for a supergun/test rig I am doing, so first the questions, then the pictures of it. Let me know if I can clarify at all:

1. What is the best way to add wires to the pins, simply solder directly to the pins and then shrink wrap? I want to add in -5V for my Midway games.

2. The video ground is missing on this harness, should I add that, or can I just use another ground? The video connector from this harness is currently connected to pin A on the Jamma connector.

3. What should I do for pins e, f, 27, 28. I know they are marked as grounds, but they are currently not on my harness. Do I need those? If so, do they ground to anything specific, or just loop back to the power supply ground?

I hope that all makes sense. Attached are the pictures from my harness:

1. yes that is the only way to connect to those is solder and shrinkwrap.
2. i would personally add the video ground wire.
3. i would add but probably not necessary.

i would never buy another one of those jamma harnesses from where you bought it because when i used to sell them they always had every one of those wires your missing populated and mine had 18awg power and 22 signal . you need to watch out for all that cheap crap out there. they won't last especially on a test bench with all the on/off of the pcbs.
 
Yeah, I would never buy one of these again, I had no clue the quality was so bad. I went through Holland Computers for it, but it's clearly just a cheap Chinese connector. It should work fine for my needs now though, especially for $11 shipped.

Anyways, I will add the video ground and the -5 via solder. Can you explain how the bottom 4 grounds should be wired please. I haven't found a good description or photo of them. Some people loop it back to the power supply, some use them for the microswitch grounds, etc.

Lastly, where would you recommend purchasing harnesses in the future, it sounds like you don't sell them anymore?
 
Run wires from the far side grounds to GND on your power supply (same as the ones that are wired up). I strongly recommend doing this, many JAMMA PCBs won't work unless they're wired up — none of the controls will work.
 
But, There are also Jamma boards that you should not ground pin 27 or e as that is for button 6 on a few boards, like my vector multi..so ground f and 29. Mike
 
I spent a good part of the morning fixing up this harness, and building my test rig. Thank you for all of the help, I will post up a few pictures of what I did this evening. I may still look into getting a better harness later for longevity, but this should be a good start for testing boards.
 
Just a word of advice, if you get too low +5v on the pcb when powered on, replace the +5v and GND cables. These Chinese harnesses barely have any copper within the cables and this is especially important for +5v and GND. Replace with something with more copper in it. The cheaper cables might work for some games but are likely to cause problems with others.
 
I feel your pain on this purchase. I bought one a while back and had to chuck it and go with a better quality one. Just picked one up from a US seller, and it's great quality (heavier guage for the power lines), and the label is in English.

As for the grounds in question:

Video ground is continuous with all other grounds, so in theory, you should be able to pull ground for video from any grounded point that is continuous with the rest of the ground system. However, it is probably best practice, as was said, to just create the ground point on the correct pin.

On the new jamma harness I got, f and 28 are not continuous with the rest of the grounds on the harness. I then noticed the wiring for those pins end in quick disconnects. That got me curious. I found that those points on the jamma edge connector of a game board ARE continuous with all other ground points on the edge connector. So, ground apparently loops through the game board, and can provide an equipment ground from those pins.
 
But, There are also Jamma boards that you should not ground pin 27 or e as that is for button 6 on a few boards, like my vector multi..so ground f and 29. Mike



Those boards aren't Jamma even if they are advertised as such.

I believe some have started advertising them as Chamma .
 
I tested all 4 of my Mortal Kombat pcbs with this test rig, and it worked out quite well! Here is a quick shot of what I did with the harness, and how I mounted it up so far. I still need to add in the ground wires on e, f, 27, and 28, but that should be easy. The harness is cheap, but I think it will hold up for a while. It was definitely worth while removing the unused pins and adding what I needed. I re-did some of the shrink-wrap as well.

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Looks nice and clean! :thumbsup:

Question: have you measured voltage on all the rails, and what are you getting? My setup is very similar, with the same power supply. I set the pot on the power supply so +5V is at +5.1. However, -5V is at -5.85V, and +12V is at +13.5V. Those values are under load. Do you see similar results?
 
Looks nice and clean! :thumbsup:

Question: have you measured voltage on all the rails, and what are you getting? My setup is very similar, with the same power supply. I set the pot on the power supply so +5V is at +5.1. However, -5V is at -5.85V, and +12V is at +13.5V. Those values are under load. Do you see similar results?

I will check and let you know!
 
On this test rig, with my MK1 board on, I measured 5.00v, -4.68v, and 14.18v. So similar to your value ratios.
 
And because I am proud, the test rig is coming along great. Today I soldered up 2 DB15 connectors to the NeoGeo/Supergun standard. All that is left is to come up with a good solution for the test/service wires, and then probably add in provisions for an extension harness using the DB9 connector method you see on a lot of Superguns. This was my first attempt at one of these, and I am learning a lot. I will probably add in a Jrok next, as this VGA encoder looks horrible.
 

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