Mario Bros -> JAMMA Board Modifications This document describes how to put a Mario Bros PCB in a JAMMA cabinet without a video inverter or external sound amp. This requires making some simple and easily reversible modifications to the PCB itself - only a few seconds with a soldering iron is required to restore the PCB so it can be played in a normal Nintendo cabinet. Note that I do not cover how to make a wiring adapter to convert the Nintendo pinout to the JAMMA standards, as this is covered in depth elsewhere. Inverting Video --------------- As you are probably aware, Nintendo PCBs (Donkey Kong, Donkey Kong Jr, Mario Bros, etc) generate inverted RGB signals - if you build an adapter to run these games in a JAMMA cabinet, the colors will turn out inverted (black areas are white, white areas are black, red areas are cyan, etc). There is an excellent document at http://www.spies.com/arcade/info/NewNintVidInv.txt that describes how to invert these RGB signals using modifications to the PCB board. As described in that document, Mario Bros has an extra set of inverted graphics data in its graphics PROM. There is a solder pad labeled CL2 at coordinate P4 on the board - if you cut this pad, the board will use this inverted palette, and will generate video that can be displayed on a normal JAMMA monitor. Sound Amplification ------------------- All the Nintendo PCBs generate unamplified sound, which is amplified by separate circuitry on the monitor. JAMMA monitors have no such facility, so typically a separate audio amplifier is required to play Nintendo games in a JAMMA cabinet. It turns out that the Mario Bros PCB already has circuitry on-board to produce amplified sound - if you look at the section of the board at coordinates P5 - P6, you'll see an unpopulated section of the board with some silk-screened white rectangles showing where the missing parts should go. If these parts are installed on the board, the board will produce amplified sound which can be used in a JAMMA cabinet. Here are the list of parts that you'll need, along with the part number that is silkscreened on the board: Electrolytic Capacitors: Part Qty Location 4.7uf/25V 1 C47 220uf/16V 2 C48, C49 47uf/16V 2 C51, C52 NOTE: There is a polarity marked on the board and on the capacitor - make sure that you install the capacitor in the correct direction. Also, you can substitute a higher voltage capacitor, as long as the capacitance value is the same (e.g. you can install a 4.7uf/50V capacitor in C47, but you shouldn't install a 4.7uf/16V cap there, or a 220uf/25V cap). Polyester Capacitors: Part Qty Location 0.1uf 2 C53, C42 NOTE: If you can't find these (they have them at www.mouser.com) you might be able to substitute a ceramic cap. Variable Resistor (Potentiometer): Part Qty Location 10K pot 1 VR1 Audio Amp IC: Part Qty Location MB3712/NTE1424 1 No part number on the board, but it's pretty obvious where it goes, in the 8 holes right next to C51. NOTE: I installed the more modern NTE1424 chip here - if you get this chip, install it so the silkscreened portion is facing towards C51. It's easy to install the chip backwards, because it's a SIP, and the NTE documentation is misleading. So, install the parts on the board. I socketed the IC, which made it easy to turn the chip around when I mistakenly installed it backwards. You probably won't find a potentiometer that fits exactly, but you can extend the leads by soldering wires to them to make it fit. Finally, there's a solder pad labeled SL1 (at M4 on the PCB). It's initially unconnected, and you'll need to close that connection by putting a blob of solder on there. Now, you are done. The board will now generate amplified audio on Pin 19 on the component side (an unmodified board will produce unamplified audio on pin W on the solder side). NOTE: I recently purchased a Donkey Kong PCB, and it has the same audio amp circuitry. I haven't installed the parts and tried it out, but the above procedure should also work on Donkey Kong. The circuitry is slightly different, and there is one fewer cap needed, but the basic procedure and parts are the same. If anyone tries this and gets it working, please let me know. Undoing your changes -------------------- In the unlikely event that you need to put the PCB back in a Nintendo cabinet, it is very simple. You will need to once again close solder pad CL2 by putting a blob of solder on it - this will cause the board to generate inverted RGB signals again. You will also need to remove the blob of solder on solder pad SL1 - this will prevent the audio signal from being fed to the amplifier circuit. It's possible that removing the blob of solder on SL1 is not necessary - I think the board still generates unamplified audio on pin W even with the amplifier circuit in place, but I haven't verified this. If anyone has any comments or questions, feel free to email me at drews-arcade_AT_aqualion.net.