Picked up this change machine at the Belleville Superauctions with the intent of modding it to dispense tokens for free, by adding a button. Ultimately I decided to rig up a switch internally that activated everytime the drawer was pushed in, thereby retaining the original look of the machine, and allowing for the machine to easily be converted back to normal operation with the simple removal of the switch.
First things first, I had to convert all of my quarter mechs to accept tokens. I would go into detail in the process, but there is already an excellent tutorial at RotheBlog.com written up by fellow KLOV'er Cadillacman.
Cadillacman's quarter to token mech conversion
Side note, I highly recommend his suggestion under optional tools, this can be a lengthy process if you have a lot of mechs to convert :)
Back to the change machine...
I was fortunate enough to not only get a good deal on the exact machine I was looking for, it also came with all relevant manuals, and lots of extras, including the calibration cards for the DBA...

So lets get Started, shall we :)

Fullsize versions of the photos below are available on the ArcadeCrusade.com webpage here
First things first, we check the manual and find that there are instructions to "test" the function of the acceptor, this is the principle we are going to use to convert this to freeplay. According to the manual, by shorting the brown wire in the 2 pin plug that connects to acceptor amplifier board, to the white wire in the 4 pin acceptor plug, it will result in the mech going thru the cycle to dispense 4 quarters. For this bill changer, it also has the option of dispensing for $5 (20 quarters). While I chose to do 4 at a time, it is simply a substitution of the brown wire for the black/white wire to make this change.
Please note these instructions are specific to the Ardac changer that changes $1 and $5. The same test can be performed on one of the $1 only changers by shorting together the brown wire and the white wire which are both located on the 4 pin plug that goes into the acceptor.
Using the testing method, we are able to make a quick modification to the changer. This simple modification is to splice into the brown wire in the 2 pin plug and to the white wire in the 4 pin plug and run those new wires to a cherry type microswitch, so that when the switch is closed, the wires "short" and the changer dispenses quarters. This is exactly what I have done.

So lets get to work and open this thing up to see what's inside:

Here I've spliced into each wire, to run a line into our switch
Here's the first 2 pin harness that I spliced (circled in red):

The red wire was cut and a wire was spliced into it.
Here is the second harness that was spliced (circled in red):

In this 4 pin harness, the white wire needed to be spliced into, so I cut the wire and made the needed connection
Taking the splice from the brown and white wires, I attached them to a slightly modified joystick cherry switch like this one:

Bent:

(you will see later why the switch needed to be bent...)

Second issue is where to mount the button to activate the changer.
While some people choose to add a button to the changer by drilling through the front and mounting a "credit button" I wanted to keep the machine as authentic looking as possible, so I did not go this route. If you do choose to go this route, there is a page in the op manual that specifies locations where the changer can be cut/drilled, and where it cannot. My solution was to mount the joystick switch to the side of the DBA such that when the drawer is pushed in it activates the switch, and dispenses the quarters.

Here is a pic of the mounted switch:

The switch is mounted on the DBA, using an existing hole. The switch is circled in blue, and the plastic piece that activates the switch is circled in green. This is attached to the DBA Drawer, when the drawer is pushed in, the plastic pushes against the metal trigger on the switch, circled in red, and closes it.

And a couple of close ups, first one open

second one activated,

To convert this to dispense tokens is a relatively easy process. For some hoppers, you will be able to just add the tokens and the hopper will function just like it is dispensing quarters. For this particular machine, there are 2 types of quarter dispensing hoppers, one that dispenses quarters and smaller (standard hopper) and one that dispenses quarters and SBA Dollar coins (SBA hopper) if you have tokens larger than a quarter (.980, .984, 1.00 etc) you will want the SBA hopper. For tokens smaller than a quarter (Namco size, .900, etc) the standard hopper will be fine.
I was stuck with the dilemma that I wanted to use .984/25mm tokens, but had a standard hopper. Fortunately, there was very little jamming in the mech, as it looks like someone already filed down the coin chute (probably due to issues with the quarters jamming), or it may have worn down on its own from years of use, it's hard to say. So for the most part, other than a little extra filing to solve the remaining jams, I didn't have to do anything to get this to dispense the tokens properly, but as always YMMV...

The final result, An Ardac C-Series Change Machine that dispenses quarters by pushing in the DBA Drawer.
If you have any questions on this modification, please email me at the contact email on the main page.