Repairing the audio on a Pac-Man arcade board

I got this knockoff JAMMA Ms Pac-Man arcade board many years back.  It’s got two ROMs instead of the authentic board’s 6 (9 for Ms Pac), and is substantially smaller than the “real thing”.  The only issue is that the audio is poor… REALLY poor.  It makes sounds but they’re… wrong and noisy.

I took over some desk space at Interlock and got to work.  (I should note that the beverages you can see here are other people’s, not mine. ;)

I traced the audio circuit on a real Pac-Man schematic (seen on my laptop’s monitor), and buzzed it out on the Yenox board to try to corrolate the two.

I had to trace four similar paths from a quad flip-flop, through a quad bidirecional switch, to the audio output.  It got really confusing at times, and took me probably a bit longer than it should have.  For the most part, they were pin-for-pin correct as far as how they were wired.  These chips have the same device (eg, a flip flop, or a logic gate) repeated 4 or 6 times.  In some cases here, the Yenox board had a different one of these devices hooked up, which added to the confusion.

This portion of the circuit uses 8 resistors to make a digital-to-analog converter. These generally work by having different resistance levels, usually something like multiples of eachother, eg,  10k ohm, 22k ohm, 47k ohm then 100kohm.  I traced out all of the lines on the Yenox board and I found out that not only were the resistors in the wrong order on the board, but they were also wildly wrong (47 ohm instead of 4.7k ohm), which you can see in this table I made:

 

You can see these resistors here on the Yenox board, right next to the JAMMA connector.  They start from the left with R1 (my notation.)  The printing on the board completely matched the resistance values that sat on them, so it’s obvious that the engineer who made this board seriously screwed it up in the design stage.

I replaced resistors R3 – R7.  I put them in with the gold band closer to the JAMMA connector, rather than the other way around.

And now it sounds near-perfect.  There’s a little bit of popping left, but I was getting tired and decided to head home for the night.  I’ll hook it up to an oscilloscope at some point and see if i can figure out which line is causing problems.

For what it’s worth, I also did the same as this on the video path DAC, seen in the above picture as the next three groups of resistors.  In the above, the group of four and then the group of five are for audio, then the next group of three is for the “red”, next three for “green”, next two for “blue”, and the remaining two are for the sync.  Again, there were some 47 ohm resistors mixed in, and notice two of the three in the “green” section are identical (red-red-brown)… which is surely wrong.  Color is now perfect on the board too!

from on February 12th, 2014Comments0 Comments

Updating my JAMMA test rig

Many years back, I hooked up a spare JAMMA harness to an old PC power supply, a monitor and some repurposed joystick pads.  (JAMMA is a standard connector size and pinout to hook up arcade game boards into arcade cabinets.  Most of my arcade game boards are either natively Jamma (Mortal Kombat, Klax, Block-out) or I have adapters to hook them up using JAMMA.  (Dig-Dug, Pac-Man, etc)).  One board that I’ve been using with it recently is a knockoff Ms. Pac-Man board, seen in these photos.

Being that I’ve been wanting to work on arcadey projects recently at Interlock, I decided to make this thing a lot less janky.

The harness/rig I have was always kind of a hack.  The video and audio wires terminated in a small box with some knobs which were meant to attenuate the signal but never really worked right.  The power switch was on this cord that came out and was weirdly fastened to the side of the power supply.  I decided to clean this up while at Interlock for open night.

 It turns out that I happened to have the right 6 pin DIN connector for this old RGB monitor (basically a Commodore Amiga 1084 clone).   So I wired up Red, Green, Blue, and Ground directly to the correct pins on it.  JAMMA spits out composite video, but this monitor takes in Horizontal and Vertical sync.  I knew that some monitors would take in composite sync on their Vertical Sync line, so I tried that… and it worked! Huzzah.

The only video issue now is that the game boards put out video that’s slightly too hot/too high a voltage, so I should put attenuation resistors inside the din connector or something…

Even though the JAMMA interface spits out amplified audio, I decided to hook up an RCA plug on the audio lines anyway, to plug it into the line-level in on the monitor.  As long as I’m careful it will be fine.

And here it is being driven by my Yenox Ms Pac-Man board with the “Horizontal Ms Pac” rom hack.  You can see the power switch sticking out of the side of the power supply there.  It’s not the most optimal thing ever, but it’s substantially cleaner than before.  Perhaps I’ll replace that switch with a nice carling switch in the future.  I’ll need this test rig for the next task, which is fixing the audio on this board.  It sounds horrid…

from on January 30th, 2014Comments0 Comments

Hackerspace In Review: 4 Year Anniversary

This last Saturday, we had a members (and friends of members) only annual meeting. Normally this is a time for everyone to hang out, eat, drink, and give presentations. Previous years, I give my personal presentation about things I wanted to do, things I failed at, things I succeeded, and things I’ll be attempting the coming year. We invited everyone this year to give a similar style presentation and the results were pretty interesting.

Our Past

A quick review of where we’re at. The organization started in September-ish of 2009, where we met in coffee shops around Rochester, to try and come up with whether or not we should make a hackerspace in the area. We came to the conclusion that we wanted to do everything from the ground up, receiving no outside financial help. At the time, we were pretty adamant about not having it called a “Makerspace” because the membership had a much wider range of interests than just making (software development, hardware reverse engineering, network security, radio, art, etc). So our bylaws stated that we will create a space focused on the interests of the members at that time. This gave us a lot of flexibility to interpret what the space would be used for. We received our New York State articles of Incorporation just about January 1st of 2010. From there we have expanded spaces starting out at a meager 200 sq ft temporary space, moving to a 500 sq ft space, and eventually to our current home which is over 1200 sq ft. Our mission statement has been the same since its inception, to provide a space to its members and the community, as well as be an organization that helps individuals developer their skills in science, art, and technology.

Our Present

As always, we had a wide range of accomplishments from our members. Here are a list of things have been working on recently:

  • Reverse engineering Ms. Pac-Man
  • Using thermite and tannerite in fun ways
  • Take EdX, Coursera, classes together: Cryptography, in-line power supplies, calculus, basic electronics
  • Creating a high power antennae with low amounts of money
  • Security research using open source intelligence
  • Using a Raspberry Pi and home sensors to graph and monitor temperature changes in your fridge
  • Artistically building a gigantic light bulb array (without burning down your apartment)
  • Converting your Perl scripts over to BASH (as an excuse to hang out with your kid)
  • Skip’s Adventures in 3D printing

This might give you an idea of the completely different background that our members have, but with the common denominator of expanding and learning more than they do right now.

from on January 13th, 2014Comments0 Comments