I recently restored a Euro Robotron, but the boardset I had kept giving me a RAM error at 1,7 -although I replaced the socket, and replaced the RAM, it made no difference.
I had heard that a Stargate board could be converted to run Robotron, so I looked into it. It's covered in the Robotron manual:
I don't pretend to understand much of whats involved, but it appears to boil down to needing to invert the signal that goes from the chip at 6F to the header board that the ROM board cable plugs into.
Inverting this signal is a pretty straight forward affair. You use a chip at 5A to do the job.
The signal comes from pin 3 of 6F. You first need to cut the trace on the under side of the board - so that it no longers travels to the header board. I used a Stanley blade and just hacked at the trace for a bit ...
The next step is to get the signal from pin 3 all the way over to the chip at 5A, so a simple jumper needs to be constructed. Here's a wire soldered on to pin 3 of 6F:
This wire then gets soldered on to pin 3 of the chip at 5A. Pin 3 of 5A is the input. Pin 4 of 5A acts as the output (i.e 5A is inverting the signal it receives at pin 3 and spitting it back out through pin 4). Here's a pic of 5A with both input and output wires soldered in place:
Forgot to say, pin 3 of 5A is grounded, so again it's just a case of cutting the trace from that pin.
All that's left to do is to get the inverted signal that 5A will now output from pin 4 over to the header board. Thankfully there's a convenient spot on the board that makes this a simple job.
Here it is, with jumper soldered into place:
Here's a couple of pics of what the board looks like now all the work is done:
And that's it. The added bonus is that with the right ROM board this will now also play Joust, Sinistar, and Splat!
Not all good news though as I'm now getting CMOS errors. Hoping to sort that out with this:
It's a Williams NVRAM adaptor which is an internal battery backed SRAM chip. It should retain the memory for about 10 years, thereby doing away with the need to use the original AA battery holder (or lithium coin cell) on the game PCB.
To install it, you just replace the original CMOS chip. It includes a 2-pin header which is for a jumper which can be used to switch between lower and upper banks of memory, so two sets of high scores and settings can be stored and accessed on the same chip.
For example, install the jumper and set the game for "tournament" settings; remove the jumper and set the game for "marathon" settings – you can then use the jumper (or wire up a toggle switch) to easily switch between the two modes and the high scores associated with each.
It's also useful because the original CMOS chips are a pain to source. Will hopefully solve my problems, be good for 10 years, and do away for need for batteries.
