I think I've shot my FDC

[Badwolf]

A bit of a check-my-working plea.

I was doing some through-hole desoldering practice on my shabby old STFM board as a) I'm really bad at it and b) I've work to do on my nice Mega board and would rather do my learning on the -FM.

The PSG chip on the -FM is partially failing I think -- one channel is dead -- and my floppy cable was falling apart.

Good practice, I'll remove the PSG and fit a socket in its stead (I already have a new sound chip), and whilst I'm at it, I'll desolder the floppy cable and put in an IDC socket.

Now, the good news is that both actually went quite well. I must be getting a little bit better. The floppy cable was a bit of a pain as half those pins are GND and they *really* wicked away the heat, so I ended up with a technique of blowing 250C hot air from a distance to gently wam a large section of the board whilst using the desolder gun. It was pretty effective without my board adopting the normal burnt-toast appearance I see when I get the desoldering gear out.

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Anyway, fitted up my floppy socket and discovered I must have binned all my old floppy cables. Managed to find one at work, but it was a single drop with a PC-style twist. I was hoping to find one of my old four-way (two 3.5, two 5.25 connectors with the twist between the pairs, but to no avail).

Anyway, this twisted cable worked well with the Gotek -- so my IDC header must have been working, hurrah -- but I wanted the old drive in here and that said no. I have a cable on order, but heady from my desoldering exploits I thought I'd simply move the floppy connector to the other side of the twist.

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It didn't work.

Worse still the Gotek wouldn't work now either. I couldn't even foment the 'cable inserted upside down' alert message it helpfully gives you.

I soldered a female connector onto the male pins of the old, decrepit, original cable. Nada.

Plugged in the external floppy. Nothing.

Put my ACSI2STM into the machine and it boots from C quite happliy.

So to my mind, this is the FDC that died. DMA probably OK as the ACSI side working, but can't see either floppy drive.

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So: check my working. Is that a sound diagnosis? Have I missed something? Is there something else I should check?

Cheers,

BW

[czietz]

It's not clear from your description: Did you install the PSG again? It drives several floppy-related signals, such as the drive and side select signals. I.e., floppy drives can't work properly without a PSG.

[Badwolf]

It's not clear from your description: Did you install the PSG again? It drives several floppy-related signals, such as the drive and side select signals. I.e., floppy drives can't work properly without a PSG.

Ah. No, I haven't yet (I was waiting for the socket).

But I'm fairly sure I saw the gotek working with the twisted cable after the PSG was already out as I desoldered them at the same time and only tested after having resoldered the socket.

But perhaps I'm having a bit of a brain fart!

Thanks for that, Christian. I didn't realise the FDC had a dependency that wasn't DMA!

BW

[Badwolf]

Thank you, Christian. That was exactly it!

I must have mixed up the order I did things in my mind. I was sure I did both of the desoldering jobs at the same time.

I'm getting old!

Anyway, socket fitted. New AY chip installed. Internal (original) and external (Gotek) both working.

And I can now format and use floppies on the original, which I couldn't before, so either my cable upgrade has helped, or perhaps that old AY chip was failing in such a way that the internal drive wasn't working. I'll have to have a look at the schematics to work out of that were even possible (the external did work).

Cheers!

BW

[ijor]

But I'm fairly sure I saw the gotek working with the twisted cable after the PSG was already out as I desoldered them at the same time and only tested after having resoldered the socket. But perhaps I'm having a bit of a brain fart!

The PSG manages the drive and side select signals. The FDC will still work regardless. A Gotek might still work without those signals depending on the jumpers. If your Gotek is configured to use the MOTORON signal, the state of the drive select signals are ignored and (I think) it should work fine but limited to single side. MOTORON is dirven by the FDC, not by the PSG.

Also depending on the cable, if the configured select signal is asserted, or even shorted, it would still kinda work.

[Badwolf]

Also depending on the cable, if the configured select signal is asserted, or even shorted, it would still kinda work.

Aha, now that sounds entirely possible. I certainly wasn’t very efficient in my ribbon connector remounting job and had a couple of goes at it.

Perhaps I had that line just shorted to GND at one point (I think every other line should be GND) and all the wiggling of connecting and disconnecting broke that contact.

BW.