In normal mode, just had a blank screen. Enable test mode and you instead get an error message showing that the ROM test had failed (even though the rom itself checks out OK with correct content)
This is because the custom Atari SLAPSTIC chip is not functioning correctly. It is used to page banks of rom into program space depending upon accesses to particular addresses.
Of course, finding a replacement for this is near impossible (although you can get after market slapstics for most of the other games), so instead I looked at ways around this.
Tetris only uses two ROM banks, so if the code could be altered to use a latch instead, then this would allow us to remove the slapstic.
There is a latch on board the PCB already, which is used for the coin counters. I don’t use these in my cabinet, so I altered the code to allow this latch to be used to page the rom instead.
To patch the PCB you will need to add three wires … starting at IC 30 C (74LS257)
- Connect pin 13 to pin 14
- Connect pin 10 to pin 11
- Connect pin 2 to IC 15 E (74LS74) pin 5
Remove the SLAPSTIC (IC 40 F) and replace the Eprom (IC 45F) with the image from this zip file.
If you use a coin counter in your cabinet then you need to remove R43 (the 1k resistor near pin 21 of the POKEY inline with the 4 dips)
So, with new version of code fitted and three wire patches, we have life …
It has been tested for a while on a couple of PCBs and we have not experienced any problems so far, but with all changes like this, there are no guarantees.