Otrona Attache: The adventure continues

[Josh Dersch]

Thanks to TonyM, I have a replacement power supply that works and I now 
have the Otrona mostly running.  (I do intend to repair the original 
power supply -- I found what looks to be a bad transistor and I've 
ordered a replacement (can't find it at the local shop.)).

The Otrona almost works properly, it just won't boot from floppy.  I 
need a bit of help debugging the floppy controller.  Thus far I've 
verified that the following are good:

- The drives themselves and the disks I'm trying to boot from (hooked 
the drives up to my PC and used ImageDisk to dump the disk contents 
successfully)
- The drive cable
- The NEC 765 controller (was originally bad! replaced with a known-good 
765 from an old PC floppy controller and this improved things somewhat.)

Symptoms are:  Drive spins up, seeks to track 0 but won't boot;  running 
the ROM diagnostics (thanks to Bob for a scan of the service manual!) 
helps narrow down things a bit:

- The "Format" diagnostic runs, which means the heads load, the drive 
seeks, and enough is working so that the Otrona thinks it's formatting.  
I've tried reading the resultant diskette using ImageDisk and it chokes 
on it, so I'm not sure it's formatting correctly.
- Reading or Writing a sector on a known good, CP/M formatted floppy 
fails.  The error code returned (4004) indicates a missing Sector ID.

There aren't a lot of chips involved in the floppy controller (about 12 
or 13) so I'm hoping this shouldn't be too hard to track down.  Any 
suggestions on where to start?  (Schematic at 
http://oldcomputers.net/Attache_Schematics.pdf on page 6).  Would it 
make sense to start investigating the chips leading back from the /RD 
DATA pin?

Thanks as always,
Josh