forums.nabu.ca

Hello! Happy new NABU owner here. Happily replaced a video memory chip (and socketed the rest of the memory since I was already in there. No I don't value my time), but now I'm just realizing I've got a keyboard issue.

Modifier keys (and CAPS) appear to be non-functional. It did work very briefly, but I haven't been able to replicate it.

SYM works fine. Every key works normally. It's just when trying to SHIFT/CTRL/CAPS any keys, only the default key character is produced. I haven't made a joystick yet so I haven't tested this functionality.

I've checked the switches themselves with a multimeter on continuity mode and they work fine.

I've looked in the Scan Code Viewer as well, of course it's the same with just the default key code being produced. <removed section about the Key/joy and Status lines in the Scan Code Viewer after reading more of the technical manual>

<removed section about the NABU spitting out 12v, measured on the keyboard PCB while plugged in and on, got 8.5v>

At this point I'm not sure what to check next to diagnose the issue. I'm assuming also that if the ROM, cable, ribbon cable, or a solder joint weren't making contact that there'd be a more obvious or wide spread issue.

If there are any other technical documents I've missed, I'm more than happy to read through them. I didn't see a schematic for the keyboard's logic board in the technical manual, and frankly I'm not 100% certain I'd know what to do with it if I did!

Thank you to anyone who can offer any assistance. I'd love to be able to use the original keyboard fully.

---

An aside: I was confused by the microcontroller. In my keyboard is an MC6803, which the datasheet I found for it says it can operate only in modes 2 and 3, vs the MC6801 which can operate in all 8 modes. But, the technical manual says that the keyboard uses an MC6801 in mode 1, and has only 3 operation modes. I'm sure this isn't my issue, I'm just curious about the discrepancy.

Well, it might end up being as simple as a bad ribbon cable or solder joint -.- I had the keyboard plugged in, and when I lift the plate with the keys to a vertical position, I get my modifier keys working again.

It was the ribbon cable! I ended up having to solder 3 wires in place of the derelict pins. I'd prefer to fully replace the ribbon cable, but right now that's a pain in the butt. I had initially avoided this because I didn't want to rip off the plastic sheet. And I was justified for that opinion, the adhesive used is almost like some kind of silicone epoxy. Absolute pain in the butt to remove. I didn't even fully remove it in most places. I couldn't get the original plastic sheet off nicely at all so I'll have to find a replacement for it.

Because soldering was a mess with the adhesive, I fully expect to need to go back in there to fix it at some point... I already had to redo one pin when flipping the PCB back over. But for now it works and that's all I'm asking for.

Good find! I had to discard a dishwasher after only a few years because they used iron rather than copper wire in the ribbon cable, and the plastic around it wasn’t steam proof, and it rusted through! Next one was a different dishwasher brand.