Jump to content
macclassic

SE/30 only reads write protected floppies

Recommended Posts

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?

Edited by macclassic
picky

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites

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?

 

 

Screen Shot 2019-11-27 at 22.01.26.png

Share this post


Link to post
Share on other sites

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. 

 

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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?

 

 

 

 

 

Share this post


Link to post
Share on other sites

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!

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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?

 

 

 

dms.png

 

Bomarc.png

Edited by macclassic
oval not in red

Share this post


Link to post
Share on other sites

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 !?

Edited by macclassic
CORRECTION !

Share this post


Link to post
Share on other sites
58 minutes ago, macclassic said:

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.

Share this post


Link to post
Share on other sites

That's what I mean when saying it might be shorted internally.

The other possibility is that the short is coming form the SWIM itself.

Without removing either the filter or the SWIM you won't find out which one is to blame though.

Share this post


Link to post
Share on other sites

FIXED

 

Many thanks for all the help as this fault was caused by was a shorting Bournes filter at RP10, but I also enjoyed checking all the traces from the SWIM chip and using a heat gun for the first time. ::)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×