Loom Making Pictorial Guide

Firstly, we need to get our equipment ready.  So, turn on the soldering iron (250oC should be adequate if you've a temperature controlled iron) and wet the sponge.  It's always a good idea to give the tip a wipe every now and then while you're soldering and especially before you've even started - solder burns and leaves black burnt bits behind which will effect the conductivity of the joint.  You'll see what I mean about burnt bits after the tip has warmed up and you wipe it!  For those without a temperature control - you shouldn't let the tip get too hot else the solder will 'cook' and your connections will be grey instead of silver, these connections WILL fail over time, so keep wiping it on the sponge.
Also, you shouldn't carry solder to the connection on the tip, the smoke you see is flux evaporating, which should normally clean the joint - you should however 'tin' the tip for good heat conduction (this means putting a small blob of solder on the tip of the bit).
Now there's two ways to do this...  Firstly, the way I do it in that I cut my wires all one length and as long as they're long enough you won't have a problem.  If they're too short then the ones which have to go from one side of the edge connector to the other side of the fingerboard won't stretch that far!  I find it easier to just snip them all one length because the next method takes too long.  Right!  Well, the next method as you can probably guess, is to measure out each separate piece of wire individually.  Now I don't mean by tape measure, just do it as you go along one piece at a time.  Hold the wire across the connection (or even solder in one end) and cut off as much as you need.  You'll need to strip about 0.5cm/5mm from each end of every wire too.
Now here's the important bit, especially if your new board is a bootleg.  Check that the pinouts you've got match the board.  Usually quite easy to do as you can nearly always see the larger tracks which are for the power connections.  As in the example opposite which is a Falcon Crazy Kong board, you can see the 3 large GROUND connections which are all 'blocked' together, they match up to the pinouts exactly.  Also, you can see the +12v connection quite clearly attached on the 5th pin going to two diodes, and then the +5v on the 9th pin also connected via two diodes.  See easy this isn't it!
Just to prove I'm not lying to you about being overly cautious!  Here's a Falcon Crush Roller board, which is supposed to use the same pinouts.  Notice that the 4 GROUND connections are on the opposite side? You have to plug the loom in 'upside-down' to get it to work!  i.e. PARTS->SOLDER SIDE and vice versa! It works though, using the same loom - which means one less loom to build phew!
Now we can start making the loom  It really is as simple as dot-to-dot to make the connections, but first we have to prepare the wire, called 'tinning' it.  This means we coat the bare wire with solder (give it a little 'twist' first to make sure all the strands are nicely together, stray strands may cause short circuits!).  When heated, the wire 'sucks' up the solder, it kind of absorbs it and makes connections more solid/ easier to make.  Now we need to tin everything else!  Put a moderate blob of solder onto each of the pins of the edge connector (or if you're lazy like me, just the ones that have connections) also tin the JAMMA fingerboard connections as well.
Now we simply join up the connections.  Do them all in order so you don't get confused, its also a good idea to stick to 'known' colour codes for wiring.  Black for ground, red for +5v, yellow for +12v, white for -5v and whatever you have left for the rest!  Although, you really should use red, green and blue for the colours!  I use yellow for sync and audio +, and all my player inputs are purple just because 100 metres was on offer that day!
The method we're using here for the connections is called 'reflowing', it may be necessary to add a little more solder to get a solid joint though... The idea is that you are coating everything in solder first and then 're-melting' the solder to form a connection, if everything is hot enough the solder should flow freely between the wire and pin. Once the connection is completely coated, remove the soldering iron but don't move the joint for a few seconds to allow the solder to cool. If you do move the joint, you will get what's called a "cold joint", this is where the solder does not make good contact across the connection.  If you're worried just look at the joint...  If its grainy and dull grey in colour, you can measure the resistance across the connection - if its any more than a few tenths of an ohm, then consider redoing the joint. This is done by first removing the old solder with a desoldering tool or simply by heating it up and flicking it off with the iron, you can then just try again.  Cold joints make a really bad electrical connection and can prevent your circuit from working.  Practise makes perfect!
Some games have what's called a 'cocktail mode'. This is where there is more than one cabinet version of the game - a normal upright, and a tabletop version. The cocktail cabinet is a two player cabinet where each player takes it in turns for their go. The controls are located on opposite sides of the cabinet and when its the next players go, the game 'flips' the screen upside-down so the other player can see it properly. Now obviously on an upright the second player doesn't need their screen flipped as both players play facing the screen in the same direction. So, rather than produce different boards for the cabinets (which wouldn't be very cost effective) the boards work in both but have either a DIP switch to set them in the different modes or have a pin on the edge connector GROUNDED. Switches work (usually) by being held 'high' meaning they are at +5v, to then be turned on they are connected to logical ground (i.e. pulled down to 0v). The reason I'm telling you about this is that for boards that have an edge connector pin that needs to be grounded to enable cocktail mode it may be an idea (if you HAVE a tabletop!) to incorporate a switch to turn this connection either on or off so you can use the PCB in either cabinet. In the example opposite, I have used a normal table lamp type switch which either 'makes' or 'breaks' the connection, therefore the pin is either grounded (connected to ground) or left high at +5v to change between the different game modes.
Another thing to watch for, which will be documented in either the manual or the pinouts - is whether the PCB outputs the correct signals for JAMMA. In some games such as classic Nintendo ones, ALL video outputs are negative and will need to be inverted to become JAMMA friendly, the picture opposite is what you'd get if you hooked Donkey Kong up without inverting the colours! Some games also do not have an onboard amplifier, and output sound at line level. This means you will have to provide some amplification of your own (see Improvements and Other Circuits).
That's kind of it really, just take it slowly and after you've finished just run over it quickly to check it against the pinouts.  Its very easy to make a mistake...  One handy thing NOT to do is not to flatten the wires against the connections, this may be a problem if you ever need to remove one for any reason.  Now's tidying time...  If you like, wrap insulation tape around the joints on the edge connector (or heat shrink tubing) its not important, but it will prevent accidental shorts - and besides it looks more professional!  Its also a good idea to label all your looms something like "Sega 16 - PARTS" so you can see what they are and which way is up!)
Lastly, when all the connections have been made - plug the completed JAMMA loom onto your board making sure that the pins on the PCB are aligned to the pins in the edge connector. This is most important especially on bootleg boards such as the Frogger opposite, notice how the edge connector has plenty of space to move and be misaligned?? We've already discussed the dangers of sending voltages where they shouldn't go! So be careful!
Now, visually check that the power connections look like they're in the right place, this is why its helpful to have them 'known' colours, makes them easily identifiable - you should always do this before turning the power on anyway, it's VERY easy to plug a loom on upside-down and damage boards. Notice in the picture opposite that there are two tracks joined in a 'U' shape? (2nd and 3rd from the left) Well, the two wires coming from the loom from those pins are black and hence GROUND, looks good to me!
Anyway... Turn the power on!  And... BINGO!!! Now don't you feel clever??!!

A couple of handy hints: