Macintosh LC III with dead floppy controller?

[walterg74]

Hi all, new to the forum came here looking for some help...

I have a Macintosh LC III that was not booting up. I replaced all the caps on the logic board, and voila, sweet chimes and bootup. 

When it started, I got the flashing questiong mark disk, meaning no OS found on the HDD. I tried with a floppy disk that’s bootable (system tools), nothing... Since I also have a Floppy Emu I thought of using that, however no matter what image I mount, it just stays there at idle and never reads...

Since I have another LC (a I) that does work (after recappping the PSU), I double checked in that one that both the floppy and the Floppy Emu worked, and they do. 

I swapped the HDD, and the LC III did start to boot (but stopped saying the installed OS was not compatible with it, blah blah). 

So I thought, ok, HDD has no system let’s install one. 

Inserted it into the LC I, and when I try to install it, the disc is not detected  I also tried disk sc, etc , nothing, the disk is jut not found so I guess it’s just dead..?

Anyway, back to the original issue, not really sure how to troubleshoot/fix if possible the issue? Can it be the floppy controller? (Swim chip?? Which is it?) something else? Because the floppy *drive* itself works, as does the one from the LC I, and as does the floppy emu, but when plugged into the floppy connector of the LC III nothing does. 

Help

 

[trag]

It is conceivable that it is the SWIM chip, but in the vast majority of cases the problem is a rotted trace from the cap goo, or residual cap goo hiding under a chip, but across connections that didn't get cleaned off.

I would try another thorough board cleaning first, and if that doesn't work, start tracing connections from the SWIM chip with an ohmmeter.  A schematic is helpful for the latter. 

 

[walterg74]

It is conceivable that it is the SWIM chip, but in the vast majority of cases the problem is a rotted trace from the cap goo, or residual cap goo hiding under a chip, but across connections that didn't get cleaned off.

I would try another thorough board cleaning first, and if that doesn't work, start tracing connections from the SWIM chip with an ohmmeter.  A schematic is helpful for the latter. 

Thanks for replying,

So to start off.. which one IS the SWIM chip? Is it the one right above the floppy connector? I *think* I cleaned it up pretty well, but will check again and also the area in general as you say. 

I also read around that the crystal plays a part in there too. Maybe it’s gone bad...?

 

[techknight]

LC 3 does not have a SWIM. its integrated into the chipset if I remember correctly. 

So its highly unlikely that is your issue. 

Have you tried to boot from floppy with the HDD connector physically removed? 

 

[walterg74]

LC 3 does not have a SWIM. its integrated into the chipset if I remember correctly. 

So its highly unlikely that is your issue. 

Have you tried to boot from floppy with the HDD connector physically removed? 

I seem to have read somewhere it uses the SWIM II chip..?

Yes, I tried with no hdd attached, same issue

Everything seems to work ok except the floppy port. 

 

[techknight]

Hmm its probably an eaten away trace because there are 3 caps that sit next to that connector which leak. 

 

[walterg74]

Hmm its probably an eaten away trace because there are 3 caps that sit next to that connector which leak. 

Well, I don’t discard any possibilities, but it didn’t seem the caps had leaked long enough to do that type of damage. 

Still not even sure where to look. 

*SOMETHING* at least reaches the port OK, because for example the floppy emu does power up, so at least voltage and gnd make it

 

[techknight]

Yes but thats meaningless as there are state lines as well as a data line. 

 

[walterg74]

Yes but thats meaningless as there are state lines as well as a data line. 

Yes that’s true, now on the other hand, the floppy connectorl ines/traces are on the bottom side of the PCB and the caps on the top. 

 

[techknight]

Then there are also Vias. 

Cant rule anything out until you inspect everything. Once its inspected beyond a reasonable doubt, then we can rule it out ;-)

 

[walterg74]

Then there are also Vias. 

Cant rule anything out until you inspect everything. Once its inspected beyond a reasonable doubt, then we can rule it out ;-)

Yeah, maybe it’s just my noob eye, but I don’t see anything that seems to be broken  :/

 

[techknight]

Yea, well. Something clearly is somewhere. or it would work. 

 

[trag]

Vias will look perfect to the eye even when they are totally corroded.  Get something like a dental pick or a straight pin and try poking the solder in the vias.  If you can poke into it then capacitor goo has eaten the solder in the via and probably the copper lining as well.    This is what happened to my IIci back around '97.   It looked fine, but when I started probing vias with a pick, most of them were hard, but one was solft, but still looked fine.

To be complete, to a really well trained eye that via probably won't look perfect, but the difference is almost impossible to detect unless you've seen it before.

 

[walterg74]

Vias will look perfect to the eye even when they are totally corroded.  Get something like a dental pick or a straight pin and try poking the solder in the vias.  If you can poke into it then capacitor goo has eaten the solder in the via and probably the copper lining as well.    This is what happened to my IIci back around '97.   It looked fine, but when I started probing vias with a pick, most of them were hard, but one was solft, but still looked fine.

To be complete, to a really well trained eye that via probably won't look perfect, but the difference is almost impossible to detect unless you've seen it before.

I guess I would need some schematics and to know where to pick

 

[trag]

Not really.  The goo doesn't travel that far.    Check the vias around the capacitor locations.   Vias are particularly vulnerable because they are low lying spots (like pot holes) where the goo can accumulate adn work its evil destruction.

 

[Zippy Zapp]

Hi,

Did you inspect the floppy connector on the logic board for any broken pins?  Also, did you try a different floppy cable?

Hopefully it is something easy and you get it figured out.

 

[walterg74]

Hi,

Did you inspect the floppy connector on the logic board for any broken pins?  Also, did you try a different floppy cable?

Hopefully it is something easy and you get it figured out.

Not at home now to show you but yes, checked bot the inside of the connector as well as the rear of the PCB and all looks good. Also, te cable cannot be the issue as the three different devices tested were tested with their own cables

 

[Zippy Zapp]

Bummer.  Well it was worth a shot.

 

[Dog Cow]

LC 3 does not have a SWIM. its integrated into the chipset if I remember correctly. 

Yeah, see here: "The new Sonora integrated controller combines the features of the V8 chip (timing, address decoding, video generation, sound control, and general logic circuits) and the SWIM2 chip (floppy disk control) while providing support for more video display modes and higher processor speeds." Source: Macintosh LC III Hardware Developer Note