exxos's Atari, Amiga & retro forum

stephen_usher wrote: 06 Feb 2025 15:51 /DKRD goes to Paula pin 37... So that may be the place to look.

Indeed. 37, 38 & 39 are all interesting from an FDD PoV, but read is a great starting point.

OK, so I decided that it was time to break out Diagrom and see if I could get any deeper into what's wrong.

First hurdle was not having any ROMs suitable to install it on, then I remembered I have a couple of Boo Bip 27C400 emulators. A quick refresh of how to program them later, and I have a working DiagRom :)

So far it's passed all the tests, so RAM, IRQ, CIAs etc report good, but it doesn't see the trapdoor RAM, but the RTC is visible as per my ATK tests.

Diagrom has an FDD tester, though it does say experimental, but I can step the heads, however there seems to be an issue with motor control. I should be able to turn the motor off and on and I can't

In the meantime I've ordered some replacement sockets for Gary, Paula, the CIA's and ROM. I have also ordered a spare set of CIA's plus Gary, Paula and Denise (It won't be Denise but handy to have spares).

Something is bugging me about the sockets even though they've had a scoosh with contact cleaner, so out with the old.

I still can't shake the feeling that Gary has left the building...

I need to go through the schematics again to follow the motor on flow, but struggling for time as work has become super busy.

U36 is buffering the motor, it's a 74LS38.


It may be useful to scope the inputs and outputs of the chip. Of course, no input would mean a Gary issue, either the chip or the socket.

rubber_jonnie wrote: 07 Feb 2025 10:05 I have also ordered a spare set of CIA's

That's a good call. The CIAs are chips from an even older computer re-used for Amiga and are I believe extremely susceptible to ESD (put it this way they break a lot, especially when hot-plugging things). At least one CIA is used (with Paula) to make up the Amiga FDC.

stephen_usher wrote: 07 Feb 2025 10:33 U36 is buffering the motor, it's a 74LS38.


thingy.jpg


It may be useful to scope the inputs and outputs of the chip. Of course, no input would mean a Gary issue, either the chip or the socket.

That is on my to do list as it goes, perhaps I can try at lunchtime, should be a quick job.

Oddly when I use my thermal camera, Gary is oddly cold compared to the rest of the custom IC's

alexh wrote: 07 Feb 2025 10:36

rubber_jonnie wrote: 07 Feb 2025 10:05 I have also ordered a spare set of CIA's

That's a good call. The CIAs are chips from an even older computer re-used for Amiga and are I believe extremely susceptible to ESD (put it this way they break a lot, especially when hot-plugging things). At least one CIA is used (with Paula) to make up the Amiga FDC.

I do take ESD precautions, but you just never know and I'd really rather have some spares handy.

stephen_usher wrote: 07 Feb 2025 10:33 U36 is buffering the motor, it's a 74LS38.


thingy.jpg


It may be useful to scope the inputs and outputs of the chip. Of course, no input would mean a Gary issue, either the chip or the socket.

So I stepped away for a second to test U36 and I can see changes at Gary but not at the output of U36 so I'm going to pull it and drop a replacement in.

Let's see how this goes.

@rubber_jonnie the floppy did boot the one working game before the post office got their hands on it...

Not sure if that helps you much though...
:roll:

JezC wrote: 07 Feb 2025 11:43 @rubber_jonnie the floppy did boot the one working game before the post office got their hands on it...

Not sure if that helps you much though...
:roll:

Well it was initially booting when I got it as I was able to boot Workbench and Amiga Test Kit. I'm going to pull U36 at lunchtime as the signal from Gary seems to be vanishing into it.

So it isn't U36...