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The Commodore Max Machine was designed to be an entry level game machine. The Max was available only in Japan. Plans to market to Germany and North America were cancelled. Not very many were sold, with units commanding large sums on ebay when they show up. The Max is semi-compatible with the Commodore C64. Or, should I say, the C64 is semi-compatible to the Max Machine. The C64 has a "Max" mode built in that lets it run Max cartridges. There are less than two dozen cartridges made specifically for the Max.
If you don't live in Japan you'll soon realize that there is no easy way to get a picture from the Max. It was designed to connect to Japanese TV sets via an RF modulator. Interestingly there is a separate audio output but NO composite video output. Most non-Japanese TV's cannot tune to the correct frequency although some newer multi-format monitor/TV's may be able to. Lukily, buried inside is everything we need, and this is my project to get composite video out of the machine.
The Max machine was designed slightly before the C64 and there are some differences. Note that the Max will work with a standard C64 power supply. The Max has only 2K of general RAM plus 1K (nibbles) for colour RAM. It has no serial connection to allow a disk drive or printer. And also more importantly, it has NO ROM. This means the machine will do nothing without a compatible cartridge installed. I also find the cartridge port is physically slightly off, and C64 cartridges may not work if inserted too far in.
The Max has a standard SID chip for audio, and a 6510 CPU just like in the C64. The Max PLA chip is different. The VIC-II chip is actually an earlier revision numbered 6566 and is designed to work with static ram (SRAM). The C64 VIC-II chip is the 6567 (NTSC) or 6569 (PAL) and is designed to work with dynamic ram (DRAM). They are not interchangable! The Max has a cassette port, power switch, power jack, RF port, channel selector, and cartridge port all on the back of the machine. There are two joystick ports... one on each side of the machine. The keyboard is a membrane type.
The trick is finding the right signals. The Max has an RF modulator designed to convert the video from the VIC-II chip to the TV. The VIC-II produces chroma and luma signals and both are fed to the RF modulator and combined to composite video, combined with audio then converted to RF channel 1 or 2 (Japanese channels). Luckily these signals are available on the motherboard and we just need to tap into them.
The Max Machine has an audio jack on the back. The SID chip in the Max only outputs mono, but the jack is actually stereo. Only one channel is connected. The other is unused. So... now we have a use for it. It's simply a matter of connecting ONE wire from the composite video output of the RF modulator, to the unused pin on the audio jack. There are no messy wires to feed out the case and the Max works and looks just like it did before. Now all you need is a stereo 1/8" jack to dual RCA connectors in order to connect the Max to a composite monitor.
Before doing this modification I would suggest you first verify that YOUR Max is the same as mine. I have a motherboard labelled "325565 REV A". If you have a newer revision see additional notes below! You will need an OHM meter. Check that the audio jack pins are not connected together. There are 3 pins: LEFT, RIGHT and GROUND. Check between each to make sure they are separate. Plug in your stereo cable and check again from the plug end. If none of the pins are connected then it's safe to proceed. Check that the LEFT pin outputs to one of the RCA jacks on the cable.
Below is a picture of the bottom of the Max board, showing the Audio jack connections (click pictures for a bigger view). The TOP is ground and the RIGHT is audio. The one on the LEFT is unused:
These are the RF modulator connections. There are two groups of 4 pins. The right-side group has the composite video output on the first pin on the LEFT, PIN 5:
This is the wire you need to add:
That's it! Now you have a standard NTSC composite video output on the Audio jack:
Note: My machine seems to have a problem with the video near the centre of the screen on some monitors. I'm not sure why that is. It's possible that some other component is failing, or that the VIC-II chip is flaky or the signal is slightly non-standard. If you try this mod on your own Max please let me know if this is the same for you!
Important Note: The VIC-II chip that is in the Max Machine is NOT the same as the VIC-II that is found in the C64! Do not try replacing the Max VIC-II with a different type or damage to the Max may result!
Composite video gives a better picture than RF, and most TV's have a composite input. The Max also has Y/C video (also known as S-VIDEO). The Y/C signals are LUMA and CHROMA and are the same as in the C64. If your TV or Monitor supports S-VIDEO input then you can get an even better picture using these signals. You won't be able to use the audio out jack on the Max, you will need to run the cables from the board out another opening like the cassette area. The LUMA and CHROMA signals are also available on the RF jack PINS 6 and 7 as shown.
After posting this page I got some feedback from Rob Clark. When Rob attempted to perform this mod he found however that his Max Machine was a newer revision. My Max Machine is a 325565 REV A. Rob's machine is a REV B. Rob found that both audio pins were in use, the second being used for "Audio In" to the SID chip. If you have a REV B board you will need to remove capacitor C74 or break the trace going to the connector. The "Audio in" feature is not needed to play Max cartridges, and there are no known add-ons that might need it.
If you have a REV B your audio connector area will look like this:
Here are the Max Machine reverse-engineered schematics for 325565 Rev B boards.
Project was started and completed on Nov 16, 2012
The following cartridges are compatible with the Max Machine:
Page created: Nov 16/2012. Last updated: Jan 30/2013, 4:00pm EST
Send comments or feedback to Steve Gray(sjgray@rogers.com)
