exxos's Atari, Amiga & retro forum

Given that the output of the chip goes directly to the internal and external floppy ports this is facinating. Because the other input to each of the NAND gates should be VCC the chip is acting as an open collector inverter. You don't have a broken pull-up resistor do you?

P.S. Just checking the schematic, /MTR0 not only goes to the floppy but it also goes to the keyboard connector via Q503 (controlling the floppy access LED). What happens if you leave the keyboard disconnected?

P.P.S. Hmm... shouldn't matter there should be 4.7K resistor (R504) to the transistor and another 10K (R506) to +5V.

Presumably that is to illuminate the FDD light on the A500 keyboard?

alexh wrote: 07 Feb 2025 13:39 Presumably that is to illuminate the FDD light on the A500 keyboard?

Yeah.

Just a silly thought.... You've not got the floppy cable connected the wrong way up? ;-)

Did you try swapping the two cia's?

Maximilian wrote: 07 Feb 2025 14:12 Did you try swapping the two cia's?

I did and it got worse, as in wouldn't boot to the insert WB screen, however Diagrom says they are good...

Nevertheless I have ordered a pair of spares.

stephen_usher wrote: 07 Feb 2025 13:44 Just a silly thought.... You've not got the floppy cable connected the wrong way up? ;-)

No, if you do that the Gotek tells you on the OLED screen. Plus on the real FDD it's keyed and will only fit one way. And just to say, the FDD connector, though not keyed, has a large friendly 1 to mark pin 1 :)

alexh wrote: 07 Feb 2025 13:39 Presumably that is to illuminate the FDD light on the A500 keyboard?

Which does indeed illuminate.

stephen_usher wrote: 07 Feb 2025 13:32 Given that the output of the chip goes directly to the internal and external floppy ports this is fascinating. Because the other input to each of the NAND gates should be VCC the chip is acting as an open collector inverter. You don't have a broken pull-up resistor do you?

I don't think so, but I'll have a look. What's weird is that this all started when I pulled Fat Agnus out of it's socket. Socket is now replaced, but everything else is the same.

stephen_usher wrote: 07 Feb 2025 13:32 P.S. Just checking the schematic, /MTR0 not only goes to the floppy but it also goes to the keyboard connector via Q503 (controlling the floppy access LED). What happens if you leave the keyboard disconnected?

No change with the keyboard disconnected.

stephen_usher wrote: 07 Feb 2025 13:32 P.P.S. Hmm... shouldn't matter there should be 4.7K resistor (R504) to the transistor and another 10K (R506) to +5V.

Understood.

rubber_jonnie wrote: 07 Feb 2025 14:22 I did and it got worse, as in wouldn't boot to the insert WB screen, however Diagrom says they are good...

Then you have at the very least one defective CIA (or defective sockets??)
Diagrom can only check a few things.

IMHO, I would wait for the CIA replacements or..
If you have a 1581 drive it also uses the same CIA...
You could probably use a C64 CIA (6526A) for testing, Diagrom will probably complain about the time tho...

You are having some bad luck with this one, normally these Amiga's are quite easy to fix.