TM848 repair?

Jim Brain brain at
Mon Jul 13 19:09:12 CDT 2020

On 7/13/2020 6:10 PM, Chuck Guzis via cctalk wrote:
> Don't mention it--happy to help out!

I am especially impressed, for a few reasons.  Backstory:

  * I snagged 2 Model 12s at a CoCoFEST! a number of years ago during
    the show auction.  NO KBs
  * I then spent too much I am sure buying extra boards from a chap
    outside Atlanta who seemed to have sold these units for years.
  * Peter Cetenski was gracious enough to get me a few bootable floppies
    to try.
  * Then, when picking up the Atlanta parts in Chicago (they came via
    someone's back seat, I by plane), Jason Timmons loaded me up with
    more Model II stuff (external drive, front bezels, and a few Model
    IIs, including a batch of KBs.
  * Finally, at Tandy Assembly 2018, I picked up 2 external HDDs for not
    much coin)
  * But, I have been sitting on all this collection in unusable form
    since then.  It's taking up valuable space and I know I don't need
    it all, so I really need to get the units working I want, and then
    move the rest to a new home.
  * Still, all of the units collectively seemed a daunting task,
    especially in light of my not knowing anything about the platform. I
    don't even know how to list a dir in TS-DOS 2.0a (or whatever it is
    called).  LS-DOS uses dir, so there's that.

Of the 4 units, 1 requires a new resistor (well, at least 1 new 
resistor), 2 were bad caps (now booting), and 1 has a good mech (swapped 
logic board with another one), but the logic board has another issue.  
Resistor is good, cap is good, and VR is outputting 11.9VDC.  The 
stepper moves when booted, and the drive motor also looks to be running 
well.  I can see the LED showing the index pulses, but not sure where I 
should start (I have it sitting in a working mech, so I know all mech is 
at least marginally OK (was booting from the mech with another logic board).


Jim Brain
brain at

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