[Coco] 26-3029 Disk Controller compatibility & repair??

[Josh Harper]

THE ONLY TANDY DISK CONTROLLER  THAT REQUIRED 12 VOLTS WAS  THE 26-3022  ALL OTHER TANDY  DISK CONTROLLERS ARE 5 VOLT
       From: Chad H <chadbh74 at hotmail.com>
 To: 'CoCoList for Color Computer Enthusiasts' <coco at maltedmedia.com> 
 Sent: Tuesday, January 20, 2015 11:23 PM
 Subject: [Coco] 26-3029 Disk Controller compatibility & repair??
   
I just acquired one of these controllers, the early model with the  MB8877A
controller insteadof the WD1779.  The first thing I did was plug it into my
CoCo2 and it did boot Disk BASIC and controlled my drives but seemed a bit
unreliable.  I had to play with the ribbon connector.  I suspected dirty
card edge but I found contradictory information online concerning this
cartridge.  Some sites say it was +12V only and therefore not compatible
with the CoCo 2 with a MPI, other sites say it's +5V so should have no
problems.which is it?

 

The screw seal had already been broken so I went ahead and took it apart and
some of the chips, especially that  MB8877A, had rusted pins. Both card edge
connectors were dirty as hell. I tried cleaning where possible and  removing
what could be removed but in the process I damaged a couple of the legs from
the controller chip and they broke.  I tried soldering on 'extensions but
the flux was fighting the oxidized remnants of the pins and by the time I
got it to stick, I think I might have damaged the MB8877A from solder heat.
Now it attempts to access the correct drive with motor on and light on, but
I don't hear any head movement and after a few moments all I get is "I/O
ERROR" in DECB.  Fortunately these chips still seem to be available
relatively cheap so I ordered one from china for $4.75.

 

Could someone please confirm if this controller is indeed  +5V only
controller so it will work with my CoCo 2 as I don't have a MPI.  Also, for
you guys that have had to clean very dirty card edge connectors, what do you
find to be the best cleaning techniques?  Thanks!

 

-        Chad

 


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