forums.nabu.ca

Hi
Does anyone have issues with an F18A video board (ie plug-in replacement for the TMS 9918A VDC) working reliably? I got my Nabu about 3 weeks ago and everything worked fine, but I wanted to use CP/M in 80 column mode, so I ordered an F18A Mk1, ie the chip-sized version of the original design from Arcade Shopper (see image below). I installed it, and it doesn't boot reliably. About 3/4 of the time it doesn't boot at all (the LED on the board doesn't illuminate), and when it does boot, about 80% of the time it goes into a mode that appears to be it waiting for info from the NABU (2nd photo). Only maybe 1 power up in 20 does it actually boot to the correct display, as shown in the last photo, which looks amazingly good on an old 17" Dell LCD. When I reinstall the TMS 9918A, the NABU boots as normal.

I haven't had time to check voltages or signals coming to the F18A yet, but wondered if this was a common problem or just me , or if anyone has any suggestions as to what is wrong.

I went to all the effort of checking the jumpers on mine to make sure they were the same as yours. They are. Crucially jumper 4 must be off.
Mine works flawlessly. Perhaps double check the thing is seated firmly in the socket and then maybe reflow soldier joints. Intermittent issues can often be something like a cold solder joint.

I do have another socket between my F18A and the socket on the motherboard.

Yeah, I gave the socket a good Deoxit bath and that didn't do anything, so I am going to start by going through the usual - reflowing joints, verifying proper contact, checking the dip switch bank is working properly, checking the voltages, looking for dodgy caps etc. I don't have another NABU to check the F18A in, but I have a TI99/4A, so I may check how well it runs in there too.

Did you get this sorted? I had an F18A here that needed the head pins re-soldered. I had the same issue in a Coleco Adam. All fixed.