Thursday, 3 May 2012


Hi all,

So I left the last post where I'd mounted the rear components ready for the JAMMA harness to be soldered to it all.

Here's Part 2 :

I'd been thinking a lot about what I wanted my Supergun to be like. For me it needed to have the colour channels adjustable, scart connection because I'm in the UK and don't have to mess about with using video encoders which I was extremely pleased about. I don't like the idea of using a video converter processing the signal to make it S-Video or something. Its not the same signal by the time it gets to the TV that the arcade originally produces, and what I wanted is the closest to the arcade experience that I could get.

I took my time scouring the net for a cheap harness but not too cheap and that it would be as fully loaded as I could get. I did contemplate making the whole harness myself with an edge connector but I couldn't be bothered to sort out what wire I would need and getting it all ordered.

I ended up getting my harness from Ultra Cabs. They have a harness that's wired to the Neo Geo MVS standard, which I didn't realise at the time and it comes with a neat edge connector cover.

When it arrived I took an evening seperating and organising the harness wiring so it would make it easier for me to get it all wired into the case. None of the wires come labelled and some of them are bunched in a way I didn't really want them grouped. So it was a matter of seperating all the tie-wraps that were around the bunches and then re-grouping them all and labelling them for easier recognition when I came to building it all up. The Edge connector is also all in chinese so you have to do some counting of pins and figuring out which side is the Component side / Solder side so you can start figuring out which wires go where.

The nervous system of the Supergun
I think the JAMMA harness looks like the nervous system of a human with the brain being at the top. Which in essence is what the harness is. The game board is the brain which connects to the top and it distributes signals to all the components around the Supergun.

Because the harness came wired for Neo Geo MVS it didn't have a line for the -5V voltage which I had to add in because I wanted it to be JAMMA compliant. It was also missing the JAMMA service and Test switch lines as well which I added to the harness.

I really wanted my Supergun to be as compatible as possible with the different types of 'standards' available in the arcade world. The main 2 being JAMMA and Neo Geo MVS for me as these are the systems that ran the games I loved the most as a kid. So adding in these extra lines to the harness were a must.

Once I got the harness sorted out I began feeding it into the case through the hole I made for it in the rear of the case, and started measuring up how much cable would be needed to reach all the components comfortably. I've seen a load of Supergun's on my research searches that look a complete mess, like the person has just jammed all the wires in there and slammed the lid shut. I really didn't want it to be like that if I could help it and wanted it to be easy to route the cables around and find any potential problems if I got any. The neater the job the better I think in a project like this.

Figuring out which wires are going to go where
It really is quite daunting when you have all the wires in your hands and thinking you have to keep track of them all so you get it wired right as first go as you can get.

After putting the harness into the case I put the PSU back in and wired it up to get a real sense of the space available then set about measuring, cutting and soldering to the components on the back panel.

Rear panel from the inside showing speaker, scart and colour adjustment
Its quite tight in there but thankfully the rear panel slides out and gives you a bit of room to get the soldering iron around without burning the insulation on the wires. The scart socket is a little bit of a tricky solder (and working out) because of all the grounds needed to be soldered to the pins which are very close together and the 2 resistors. Again I tried to make the wires as neat as possible in the space I had available.

The rear panel wired up and ready to test
I wired up the rear speaker with an attenuation circuit shown on one of the wiring diagrams. If you are planning on routing the audio out through your Scart connection you need to make an attenuation circuit to lower the amped audio otherwise you will blow the speakers on your tv. Because arcades aren't the most graceful of technology and with the arcade cabinets having biggish speakers with no volume control the game boards output really loud, generally non-adjustable audio. So you need to lower the volume so it will not kill your tv.

For me I didn't want to run the risk of blowing my tv speakers but didn't want to mount a speaker inside the case, I opted for an audio out socket to connect some external speakers. Because I was a little worried I would blow my external speakers I made the attenuation circuit to protect them a bit.

The Supergun all wired up with audio and sound I eagerly ran up to our Hobby room and plugged in the one JAMMA arcade game I had to see if my wiring had all worked.

I plugged everything in, tentatively switched the power on and the standard scart channel blue colour on the TV switched over to black. Woo! The tv was recognising a video signal! But where was the picture?!? Crap! First thing I thought was, I'd done it wrong. I was going to have to re-wire the scart socket. I turned it all off and quickly checked over the JAMMA connection on the board, scart cable correctly seated in both Supergun and TV and flicked the power back on. Again, black screen. Poo! I slumped down to a seating position on the floor and out of the corner of my eye I saw some very very faint writing on the tv screen. What an idiot!!!! I'd turned my RGB adjustment dials all the way down, a quick turn on them and the screen burst into life and the game was playing! :D

Scart connection wired up first go! I gave myself a congratulatory High-five. It was a reality!
The Supergun's first test with my only arcade game, Teki-Paki
There was no audio though. That shouldn't be too hard to fix. I headed back to the kichen, cut the attenuation circuit out and wired the audio wires straight to the speaker output. Went back up stairs and what do you know?! Audio now works too!

Also you might be able to see on the last photo that there is a little green light on the front of the Supergun. I wired a green LED to the +5V output on the PSU with a 220k ( if I remember right ) resistor so that I would have some indication that the power was on and working when the rear switch was flicked. Otherwise there is no knowing the power was on and from the get-go I would be wondering if it was powering up or fallen down at the first hurdle.

For me this test was a massive MASSIVE achievement. A few months ago I hadn't got the faintest clue how to solder and was too scared to even try it. After a very short time where I've only done some console mods in my kitchen I'd now built an arcade machine that works!

I decided to leave it on a high and put the soldering gear away and wait for my front components to turn up for the next step of the Supergun's creation.

To say I was itching for the stuff to turn up was an understatement!! :D

I'll get writing up the next part in a few days.


No comments: