[Coco] Disto SC needed

[Darren A]

Roger,

Do you hear the heads move before the crash? Does it seem to crash at
a point where it would actually be reading a sector (seek to the
correct track completes successfully)? This usually indicates a
problem with the HALT or NMI, but those problems are normally isolated
to an individual CoCo (CPU). You say this happens with several CoCos
which has me a liitle perplexed. You can try this BASIC one-liner to
test the controller's HALT circuit:

POKE &HFF48,3:POKE &HFF40,128

The CoCo should freeze for 8 seconds before the OK prompt appears
again. If you see the typical crash behavior immediately then the
problem could be related to someting with the HALT circuit. If it
occurs at the 8 second mark then it could be something related to the
assertion of NMI.

Is this your only controller? You could always try swapping a 1773
from another controller (not including the 26-3022 or early version of
the 26-3029). You can also make an offer on one of these eBay
listings:

<http://cgi.ebay.com/LSI-WD1773-PH-WD-28-Pin-Vintage-IC-LIMITED-SUPPLY_W0QQitemZ320272628063QQcmdZViewItemQQptZBI_Electronic_Components>

<http://cgi.ebay.com/1773-WD1773PH-WD1773PH-00-02-Floppy-Disk-Control_W0QQitemZ140133211486QQcmdZViewItemQQptZBI_Electronic_Components?_trksid=p3286.m20.l1116>

Darren

----

On 11/14/08, Roger Taylor  wrote:
> Well folks, I don't know what happened but my Disto Super Controller
> I which hasn't been able to write suddenly started causing read
> errors a while ago.
>
> Doing a 'DIR' on any floppy either causes the CoCo to crash or the
> screen will clear, the video will glitch real quick, then you get the
> cursor.  I've tried 3 cables, recleaned the contacts (which were
> already clean), tried 3 CoCo's and 2 different drives with the same
> results.  I even reseated the chips.
>
> Please tell me this is just a capacitor or something I can
> replace.  :)  Jeez.  I was 1 minute from burning an EPROM and was
> overly anxious to make some progress.
>
> I don't understand what causes CoCo floppy controllers to suddenly
> break like this but over the years I've had many controllers do about
> the same thing, crash the CoCo when trying to read a disk.  In the
> pile they went.
>
> If this sounds like a common WD1773 problem, where can I find one?
>
> At any rate, I desparately need a Super Controller with the MEB
> connector so I can use my MPROM attachment.
> --
> Roger Taylor
>