Jamma harness ground connections?

[kingtreelo]

Hi, so i need to tie all my ground connections together on my jamma harness and other than running a little wire, is there an easier way to do this?

I would guess there is a connector that you can put one ground wire in that bridges the 2/4 pins?

Does something like that exist, and if so, what is it called?

 

[John Bennett]

The idea really is to have separate cables back to the PSU for every ground pin, and in the same way have separate cables for every 5V, 12V and -5V pin.
This reduces the voltage drop across the cables.
Otherwise you risk different voltages being applied to different games, depending on their power draw, unless you're going to twiddle the PSU dial every time.

 

[favouredson]

As JB stated, the more the merrier.
If your cabinet loom is properly wired it will also make up for deficiencies in any JAMMA adaptors you might use.

 

[kingtreelo]

i'll take a look, there arent any loose wires from the wiring loom that i can see, but TBH, i havent really looked that much

 

[kingtreelo]

so ive had a look today and cant see any spare wires at all to hook up to the harness, i was expecting to see a few ground wires on the loom that were loose but nothing...

any ideas?

 

[favouredson]

Ideally, you would add wires from the PSU to the connector.
If you are unable/unwilling to do this then you could always do a bodge and make up a JAMMA to JAMMA adaptor with all the ground pins interconnected.

 

[kingtreelo]

Ideally, you would add wires from the PSU to the connector.
If you are unable/unwilling to do this then you could always do a bodge and make up a JAMMA to JAMMA adaptor with all the ground pins interconnected.

could i not just connect the grounds that are already wired to the other pins?

im not even 100% this is going to fix my problem but its worth a shot

 

[BigP_BigP]

could i not just connect the grounds that are already wired to the other pins?

im not even 100% this is going to fix my problem but its worth a shot

Totally agree with all the above posts. Commonly grounding issues stem from poor quality wire (too little copper). This is a particular issue on some of the eBay/Aliexpress JAMMA harnesses. I restored(?) a Chinese clone blast city a year or so ago to make a dedicated DDPDOJ cabinet. In doing this I had to totally remove the gnd and 5v wires (apart from the thinner button grounds) and upgrade the wire thickness to 16awg. Typically the cheaper harnesses look like 18awg but when you cut the wire it only has the copper of a 20-24awg wire the thickness comes from the shielding. Something similar may help in this situation. (Excuse the cab pic post... any excuse)

 

[kingtreelo]

so im revisiting this, had a busy few weeks, so are people suggesting i should have all 8 of my ground pins on the harness wired back to the PSU?

apologies if im being a bit stupid here, but im not sure how i would fit 8 wires onto the PSU single ground connection, really want to get this up and running with my pi2jamma rather than being limited to just the PCBs that came with them

 

[qjuk]

You don’t need 8 ground wires running back to the PSU.

I normally have 4 decent quality ground wires from the PSU to the JAMMA edge. 1 wire to connect both pins A+B, 1 wire to connect pins 1+2, 1 wire for pins 27+28 and 1 wire for pins e+f. I solder the ground wire in the middle between the 2 pins and cover with heat shrink tubing. You can also bend the JAMMA connector solder pins slightly towards each other to make to soldered bridge connection easier.

 

[kingtreelo]

You don’t need 8 ground wires running back to the PSU.

I normally have 4 decent quality ground wires from the PSU to the JAMMA edge. 1 wire to connect both pins A+B, 1 wire to connect pins 1+2, 1 wire for pins 27+28 and 1 wire for pins e+f. I solder the ground wire in the middle between the 2 pins and cover with heat shrink tubing. You can also bend the JAMMA connector solder pins slightly towards each other to make to soldered bridge connection easier.

so i have wires on about 4 or 5 of the pins, on all 3 of my jamma connectors(they are all identical harnesses and wires from the 80's), they seem pretty tightly crimped on, i just dont know where to begin to bridge them or take the current ones off and replace them with some sort of adapter that connects the earth to 2 of them at a time

the problem is that my wires are connected up to just one pin..and not both of them

 

[qjuk]

I’ve just pulled out a scrap connector and a scrap piece of wire to show you where I mean the wire is soldered (bridged) between the two pins.


A solder blob should bridge the two pins nicely.

Another technique is to strip the wire back a bit more so you have more of the copper exposed. Bend the copper end of the wire into an “L” shape. solder first on one pin, then the end onto the second pin.


Tidy up with some heat shrink tubing and you should be all good.

 

[kingtreelo]

i guess the worst thing that can happen is i will need to buy a new harness and wiring, which may be the easier option, i'll give the solder thing a crack and see how i get on