exxos's Atari, Amiga & retro forum

So I decided to test every key on the keyboard, and found that 2 work.

Key 7 stops the screen flickering, though I have no idea why, and the - key causes it to drop into what looks like a monitor mode with four zeros top left and a hex value to the right of it, a bit like this:


0000 3B

All a bit odd.

rubber_jonnie wrote: 20 Mar 2024 15:55 So I decided to test every key on the keyboard, and found that 2 work.

Key 7 stops the screen flickering, though I have no idea why, and the - key causes it to drop into what looks like a monitor mode with four zeros top left and a hex value to the right of it, a bit like this:


0000 3B

All a bit odd.

EDIT: What happens when I press the - key is what should happen when I press the M key at the start menu.

Also I just nearly got to boot to basic, and I got as far as memory size? but hitting return only gave me a - sign, but other keys were working. It's odd that I wondered if my shift lock switch was causing issues and since I removed it the flashy screen has gone and it's solid as a rock, but none of the keys work again!!! Grr.

Annoyingly I didn't get pictures!!!

I think this is now just a faulty keyboard issue, and the KBD logic is just 4 chips so I'll have a look at the soldering and make sure nothing is wrong.

OK, well that was annoying. I decided to reflow the sockets for the LS125's and flipped it back over, powered on and got a screen full of garbage again! Whaaat!!!

Some troubleshooting later I find that if I take U4 & U5 out (These send some of the keyboard data onto the data bus) and the machine boots to the D/C/W/M ? prompt again.

So I test the 2 74LS125s I just took out and bothe are bad. Whaaat!!! again.

So I need to order some more and see what happens when I put working ones in. Maybe it'll work. Perhaps, fingers crossed.

Would explain why the keyboard wasn't working though.

EDIT - One of the LS75's is dead too :pullhair:

Oh, that's annoying! You've not been rubbing your feet on the carpet before touching the board whilst playing with a Van de Graff generator have you?

stephen_usher wrote: 20 Mar 2024 21:42 Oh, that's annoying! You've not been rubbing your feet on the carpet before touching the board whilst playing with a Van de Graff generator have you?

I don't even own a Van de Graaf Generator (Note to self: Buy Van de Graaf Generator)

I think something else hinkey is going on with the KBD side of things, but need the spares before I can start to look into it. Hopefully they'll be here soon.

You do seem to be having a high TTL death rate somehow.

stephen_usher wrote: 20 Mar 2024 22:08 You do seem to be having a high TTL death rate somehow.

Yeah, it's not good. Need to go through the whole kbd circuit and see if I can figure out what the heck is going on.

Bloody hell. I just tracked the /RKB line from U20 to where it sends an enable signal to the LS125s and LS75s that form the KBD circuit.

That's dead too...

No signal on the LS138 and subsequently none

More ordered.

WTF is going on?

If I swap with one of the other LS138s I get a good signal. This is all rather annoying.

It does sound like a power supply issue. I bet all those logic chips shared the same GND or +5V

PhilC wrote: 21 Mar 2024 11:28 It does sound like a power supply issue. I bet all those logic chips shared the same GND or +5V

I don't think so, it's a bench PSU with the voltages and OCP dialled in. Maybe just crap chips. Probably re-branded MOS ICs :fire1:

And of course I don't have any spares in stock...