SE/30 only reads write protected floppies

[macclassic]

I've just got another SE/30 which will only read write protected floppies and doesn't recognise unprotected floppies, but asks to format them, and when I try  this it makes the usual chugging sounds but then fails at the end and says the disk is bad.

Connecting a, known to be good, floppy drive makes no difference and a  SCSI Zip drive also works fine on this machine.

And the logic board has been recapped.

Help, where should I start and what should I be looking at?

 

[Crutch]

That is weird. This happens with ANY floppy drive you connect? I’m going to guess cap damage around the SWIM chip could be the issue maybe?

 

[macclassic]

Yes, I actually tried two floppy drives with the same result and at the moment I'm checking the traces from the SWIM to the ribbon connector

 

[macclassic]

I'm checking for continuity from the SWIM chip to other components but cant get my head around what pins 37, 40, 41 and 42 connect too using Apple schematics.

Can someone point point me in the right direction on these four pins?

 

[sam1729]

Those are Address lines 9, 10, 11, 12, which you'll find at C11, A13, C10, B11 respectively on the 68030.

 

[macclassic]

Still stuck, coming from the 68030 chip?

 

[sam1729]

If you're looking at the underside of the board, with the I/O connectors at the top, and the ROM SIMM at the bottom, then the bottom-left pin of the 68030 (UK8) is A13, and the top right is N1.

So, C11, for example, is the third column from the left, and the third pin up. 

 

[macclassic]

Wooo! probing both sides of the board  is getting tricky but i have to check them all, thanks

 

[macclassic]

They all check out and there doesn’t seem to be any damage around the SWIM chip, so now i’m stumped!?

 

[BadGoldEagle]

I know this’ll sound stupid, but have you tried pulling the swim out of the socket and putting it back in? I’ve had a similar problem with one of my SEs. I thought the swim was a goner until I swapped it back and fourth with a known good one, and the defective chip started working fine again after a few tries.

 

[macclassic]

I read about  your experience somewhere else on the forum but don't own a heat gun or any kapton tape, ...... and  worry I might ruin the board, ... but maybe I should first try lifting a SWIM off a beyond repair board to get the feel of doing it?

Are there any tricks to lifting a chip of the board, like maybe a quick flick with a dental pick?

 

[BadGoldEagle]

I completely forgot about the SWIM on the SE/30 not being socketed... In that case I'd test the connection between every leg and its corresponding pad on the bottom or with a VIA. 

Alcohol can help getting rid of residues such as cap goo etc. Use a Q tip or an old toothbrush to clean the legs. 

A quick flock with a dental pick will more than certainly result in a lifted pad, and you definitely don't want that!

 

[LaPorta]

Another possibility: check the Bournes filters per Pina's guide and see if they all check out. Always possible that there is an issue there.

 

[macclassic]

Thanks, will do

 

[macclassic]

The Dead Mac Scrolls says check/replace two Bournes filters for the SE, so with the SE/30 I'm guessing the filter to check is RP10 as shown on the BOMARC page

Does anyone know the typical values across the pins of this filter?

 

[Bolle]

Resistance should be 47ohms.

Also check each pin for shorts to other pins or ground.

 

[macclassic]

Just tested RP10 again and I'm getting 000.2 ohms across pins 1-20 and 10-11 and 47 ohms across most of the others

but 28.6 ohms on pins 5 and 16 to ground !?

 

[Bolle]

but 28.6 ohms on pins 5 and 16 to ground !?

That shouldn't be the case. Something is broken there. Also this is the WRREQ signal on the SWIM, kind of makes sense...

Remove the filter from the board to check if the filter itself is shorted internally or if the short is coming from somewhere else.

 

[macclassic]

Or a short to ground on pins 5 and 16,