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TRS 80 Model II - restoration project


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  TRS 80 Model II - restoration project by Bill Degnan - 10/05/2008 09:09
I had not used my model II for three years, and with this thread in mind I set up the old beast for a routine test. I try not to let any working system go too long before I re-run for a few hours to refresh the electronics.

Anyway...I must have waited too long, she does not boot any more. The system powers up,but will not attempt to read the disk drive and there's nothing sent to the CRT.

So far I have done little other than open the system and quickly inspect it. The CRT tube fires up (strong glow), so I assume that the issue lies with one of the four system cards (there is no motherboard). I have not done any further testing.

If I have an update I'll post it.

  TRS 80 Model II Restoration Update by Bill Degnan - 10/05/2008 22:19
After re-seating the chips and checking all of the conections, etc. I was able to get farther. Now the screen comes up, but I cannot boot any disks, even previously thought-to-be-working disks. Instead I get the following error:


Here's what I found on this error:

Floppy disk
controller error.
a. Defective a. Try a different
diskette. diskette.
b. Floppy disk b. Turn on the
expansion unit. floppy disk
not on. expansion unit.
c. Defective FDC c. Contact RSSC.
Chip or Drive.

NEXT: Replace the disk drive with a replacement. Note - I am pretty sure I have at least one working disk, and I have tried booting with both a terminator in the expansion drive port AND also with a expansion drive attached to the port. I don't think that this is the problem.

I have noticed that the system will notice if I put a disk in the wrong way, so I believe the controller is OK (or more likely to be). The drive belt spins the disk, but the drive motor does not move the head unless I extend it out manually. In this case it just returns it to track 0 and stops.

  Testing Model II disks in a Model 12 by Bill Degnan - 10/12/2008 14:03
Last night I got my Tandy Model 12 running, and I used it to test Model II disks because that system still does not work. I have pretty much decided that the problem with my Mod II system is the drive itself not the controller. The only 8" drives I have are not compatible with the older Model II drive power connectors. I prefer to find the correct drive rather than kludge something.

  The felt pads on those drives... by Aaron Brockbank - 10/30/2008 22:23
The pads on the non-headed side on single-sided Shugart drives tended to scratch the oxide from the disks, and the build up would then cause the other (data) side to delaminate under the previously working head.

Have you considered replacing the pad?


  flet pads by Bill Degnan - 10/31/2008 11:38
I checked the pads, and I was able to clean them, that's not the problem here (or at least it's not THE problem).

  TRS 80 Model II Pictures / more tests by Bill Degnan - 11/16/2008 22:46

New Pictures TRS 80 Model II and Model II Disk System

Futher Testing:
Knowing that the Model 12 can read and run disks from a Model 2, I took a batch of Model II disks and tested them in my TRS 80 Model 12 to confirm that the disks were OK. I do have a number of good disks.

I have been told that I can take the disk drive out of the Model II Disk System drive (see link to new pics above). I will do this if I cannot find a replacement from a system chassis, but at this time I want to avoid disabling a drive to fix a computer.

  TRS 80 Model II Disk System by Bill Degnan - 02/13/2010 13:05
For fun I am going to try to bypass the internal drive and boot from TRS 80 Model II Disk System.

TRS 80 Model II Disk System with bay 1 filled (left drive) = logical drive 1.

To boot from the external drive, I need to change the drive assignment jumper from 0 to 1. I also need to disconnect the internal drive from the chain. I assume the external drive has a terminator.

  TRS 80 Model II Update by Bill Degnan - 08/07/2013 17:28
TRS 80 Model II CP/M
Boot screen for the Pickles and Trout version of TRS 80 Model II CP/M 2.2

Although I always swear that I will never work with a Model II again, I also can't stand not having a working system lying around, so I assembled a "Frankenstandy Model II" from parts. Lesson learned - don't use Gorilla Glue to attach keyboard replacement pads. That said, it's good to have a working Model II again. I also have a working expansion drive system with three drives. Two work reliably, the third needs some tweaking.

So...would it be much trouble to migrate some model III programs to the Model II? Wonder what's involved???



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