LC 475 floppy disk controller issues

[jammi]

Hi, I recently recapped my LC 475 that was having all kinds of stability woes and extremely unreliable SCSI before recapping. Now it boots solidly from a SCSI2SD (and HDDs), but the floppy disk controller no longer works. I used it extensively with FloppyEmu before recapping, so I know it did work, but now it's stuck with no access to the floppy and it seems to think there's a locked floppy inserted. Therefore, I can't boot, because Finder keeps complaiting about that the floppy can't be initialized because it's locked and therefore won't allow to proceed; it's just looping there with a few seconds of delay between pressing "OK" in the error dialog. I can see from the screen of FloppyEmu that the Mac doesn't even try accessing the drive. So, what should I do?

 

[bibilit]

probably a micro-switch faulty or stuck down

 

[jammi]

probably a micro-switch faulty or stuck down

No, definitely not. Like I said, I've primarily been using it with the FloppyEmu; you know, the device by Big Mess of Wires. There are no microswitches on it and the floppy drive itself is as dead, yet both did work before and both work with other Macs. I've therefore narrowed it down to either a controller issue or something else on the motherboard. The motherboard per se is clean and there's no visible damage anywhere.

Since I'm not very familiar with this board model, there don't seem to be a dedicated SWIM chip like on some other models, so I guess the controller is on the large VLSI chip among other integrated devices such as the display controller. The question is, is someone familiar with these boards and have encountered / resolved an issue like this before, or am I out of luck?

The recapping was done with my hot air SMD rework station and that appeared to work fine as it did with numerous other machines I've recapped. I also tried reflowing every joint on the board in an attempt to resolve the issue, but no luck.

 

[cheesestraws]

My first port of call personally would be to clean around the pins of the ASIC with isopropanol or something to make sure that something conductive hadn't got wedged between any pins.  Might also be worth seeing whether pin 20 of the floppy connector (which according to the pinout I have here is the 'write protect' pin) on the board is shorted to anywhere it shouldn't be?

(Caveat: I am a rank amateur at this and other people here will likely have better ideas)

 

[jammi]

My first port of call personally would be to clean around the pins of the ASIC with isopropanol or something to make sure that something conductive hadn't got wedged between any pins.  Might also be worth seeing whether pin 20 of the floppy connector (which according to the pinout I have here is the 'write protect' pin) on the board is shorted to anywhere it shouldn't be?

I've cleaned the entire board with isopropanol after working it, it's spotless. Also no obvious shorts anywhere and I reflowed all the joints on the board (using hot air). I also did the rework on a anstitatic table surface and shouldn't have caused situations of static electricity. I'll try inspecting it through a magnifier in case there's something I missed with bare eyes although nothing on these old boards is so small it'd require magnification.

 

[cheesestraws]

That's fair.  I was mostly trying to work out whether there was a simple electrical fault between the SWIM and the port, but actually if it doesn't even attempt to access anything on the drive then it probably isn't, is it.  Sigh.

 

[jammi]

Anyhow, the problem still persists. I'd greatly value some information of capacitor traces since I think that's the most likely source of issue. If someone manages to remove caps without damaging the pads and taking a photo of that, it'd be perfect.

 

[jammi]

I figured this one out. Right next to one of the caps with intact pads there was slight solder overlap with the traces next to it, so the solder joint was interfering with signals going to the floppy drive and sound chip. I removed the offending cap; its offending leg was off by a mm or so, therefore over the traces, straightened it up and removed excess solder from other caps too and now it works like a champ.

 

[imactheknife]

I figured this one out. Right next to one of the caps with intact pads there was slight solder overlap with the traces next to it, so the solder joint was interfering with signals going to the floppy drive and sound chip. I removed the offending cap; its offending leg was off by a mm or so, therefore over the traces, straightened it up and removed excess solder from other caps too and now it works like a champ.

I know this is older, but which caps? my floppy isn't working, no other floppy drives work with this system either. I tried different cables etc. The drives work fine in other machines