If Galaxians looks fine, and Frog looks fine, but many of the other games have totally wrong graphics, then the chances are that you have the cables the wrong way around on the CPU board.
Most of the problems experienced with the multigame so far have been down to these cables and connections. Check the installation page and make sure that you have them connected the right way round.
If, after installing the multigame, the missiles and shells are not very bright. check out the three resistors at R58, R59 and R60 (near the dip switch) – these should be 100 ohm (brown/black/brown) but other values seem to have been used. I have found 200 ohm, and one early mutligame user had a board with 270 ohm installed. Replacing these with the correct 100 ohm returns them to normal.
Not a common occurrence, I’m glad to say, but I have seen one multigame board that was totally dead, and the user just received a screen of random graphics on power up. After talking to the user, he mentioned that the CPU board may have been plugged in back to front. If you have done this, you will need to replace three of the IC’s – the two 74573 latches and the logic chip (a GAL16V8 programmed with the code provided in the download)
There is a modified version of the galaxian memory test built into the menu code. This memory test also tests that the NVRAM IC fitted to the main multigame board is functioning correctly. If an error is detected, then rather than display a ‘RAM ERROR’ message, which is easy to miss, it instead fills the screen with a single number.
1 : Program ram failure (7N / 7P)
2: Video ram failure (3F / 3H)
3: Object ram failure (4F / 5F)
4 : NVRam failure (Multigame board)
Moon Cresta Memory Map
Some boards have had memory mapping hacks done to them and will not be compatible with the multigame. The most common of these is the change to run Moon Cresta (or Eagle).
This usually involves a couple of changes.
The first of these is at position 8E (74LS139) and affects pins 4 and 5.
For Galaxian, the track should go to pin 4 (visible on the bottom of the board) whereas for Moon Cresta the track goes to pin 5 instead. This change moves the memory and IO up $4000.
This can be done either by cutting the track and using a wire link instead, or I have also seen it done by cutting pin 4 on the chip, and then soldering pin 4 and 5 together on the solder side. If this has been done, you need to re-build the broken pin (in extreme cases you will need to replace the chip) –
The other change is to the interrupt enable and is controlled by 9N (74259) – in this case instead of pin 5 being used, pin 6 is instead (moving the interrupt to $x002) – it is likely to have been done in the same way as the previous hack, and will need reversing to normal before you can use the multigame.