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TRS-80 Model 3 Disk Drive Issues

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Kilgoreroot

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Jan 25, 2022
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Hi guys. I'm somewhat new at repairing these old Tandy machines and I was hoping someone might be able to help me out. I recently got a TRS-80 Model 3 with 48k of ram and two built-in disk drives. I believe the disk drives are the originals. When I first got the machine, it had quite a few issues, but with a little reading and a scope, I was able to fix most of them, and at some point, I had it booting from disk, and everything looked great, however, disk drive #1 didn't work It seemed there was an issue with the stepper motor because it made a different sound when the stepper motor was running than the working one. I took that drive out, and the stepper motor was very difficult to turn, so just as a troubleshooting step, I took out the stepper motor from the good drive and put it in the bad one. This didn't work unfortunately, so I assumed I'd just have to buy a new one. But then then when I switched the stepper motor back to its original drive, all of a sudden the drive didn't work. Now when I power up the machine with either of the drives hooked up as drive 0, the drive spins up, and the stepper motor pulls it back to its track zero position, but then that's it. No matter what I do, I can't get it to do anything after spinning up and pulling the head back to the zero track position. It's definitely not jammed up or anything, and it's for sure hitting the little track zero tracking button.
Does anyone have any troubleshooting ideas?
I ordered a couple new drives, and my plan as of right now is to just try those when they get here, but If I can, I'd like to get the original drives working.
Thanks in advance for any help you might be able to offer
 
kilgoreroot,
First thing is to tell us what the Manufacture's name is on the Drives. I assume they are Double Sided
Double Density. Likely they are Tandon TM-100-2A, or the Texas Peripheral Incorporated (TPI a
Tandon knockoff), but could be another manufacture.

If the Drives are Tandon TM-100's Open the floppy Door and look at the center hinge pin. You should
see a full length Brass Pin for the Hinge. If you see two short White Nylon Pins, those need to be
replaced ASAP, as they will become misaligned and break the Hinge. Replacement parts are available
on ebay.

You should have just worked on the defective drive. Swapping the stepper motors is what caused the
problem with both drives. Both are likely out of alignment, and both now don't have the Track Zero Sensor
properly positioned. So, it's a double whammy. Alignment needs to be done first to get the CAT's EYE
Pattern on Track 16 for proper Radial Alignment, then properly set the Track 0 Sensor, on both Floppy's.
The problem is not having the Dysan Alignment Floppy available to properly set the Radial Alignment.

You really need to be able to boot a Diagnostic Floppy to work with the Drives, but that's not an option.

Do you understand how to get to Cassette Basic (located in ROM's) so you can do a bit of testing?

Boot to Cassette Basic and do the following tests:
Press the BREAK key to stop execution.

DRIVE 0 is the UPPER DRIVE.

5 REM Run Drive 0
10 OUT 244,1: GOTO 10

5 REM Run Drive 1
10 OUT 244,2: GOTO 10

Both drives should run and spin the floppy's, until you depress BREAK.

Now, step the head(s) from track 0 to 39 for Drive 0, then Drive 1.
5 REM Drive 0
10 OUT 244,1: OUT 240,3
20 FOR T=1 TO 700: NEXT T
30 OUT 244,1: OUT 243,30: OUT 240,19
40 FOR T=1 TO 700: NEXT T: GOTO 10

5 REM Drive 1
10 OUT 244,2: OUT 240,3
20 FOR T=1 TO 700: NEXT T
30 OUT 244,2: OUT 243,39: OUT 240,19
40 FOR T=1 TO 700: NEXT T: GOTO 10

The Floppy Drives Head carriage should move from the outer position to the inner position and loop.
If the head stays at track 0 or at track 39 and keeps hitting the stop, depress the BREAK key and check the
operation of the Track 0 Detector circuit.


TRACK 00 DETECTOR

To verify the track 00 detector circuit is working, position
the Disk Drive head carriage assembly away from track 00
before turning ON the Computer. Connect a Logic Probe to
pin 10 of Interface IC U3 on the Disk Drive board. Turn ON
the Computer. Type in and run the following Basic program.
The program turns ON Drive 1, moves the head back to track 00
and two numbers appear on the Monitor screen. The first number
appears when the head is off track 00 and should be 2, the second
number appears when the head is on track 00 and should be 6.

Do not put a diskette in the Disk Drive.

5 REM Drive 0
10 OUT 244,1: PRINT INP(240): OUT 240,3
20 FOR T= 1 TO 600: NEXT T: PRINT INP(240)

5 REM Drive 1
10 OUT 244,2: PRINT INP(240): OUT 240,3
20 FOR T= 1 TO 600: NEXT T: PRINT INP(240)

If the Logic readings are not correct at pin 10 of IC U3, check
for Low Logic reading on pin 10 of IC U3 when the head is on
track 00, 01 or 02. Check for a High Logic reading when the
head is on track 03 or higher. If the logic readings are not
correct check P 11 for good connections and check the
Track 00 Switch (S2). While the program is running, check
for a Logic High, on pin 15 of IC U3, when the head is not on
track 00 and a Logic Low when the head is on track 00. If the
Logic readings are not correct check IC U3. If the Logic
readings are correct on pin 15 of IC U3, check for a High
Logic reading on pin 5 of IC U95 when the head is not on
track 00, and a Logic Low when the head is on track 00, when
the program is running. If the logic readings are not correct,
check Connector J2 on System board, and Connector J2 on the
Disk Drive Board.

That should get you started.


Larry
 
Looks like I have a couple of typo's in the code.

Now, step the head(s) from track 0 to 39 for Drive 0, then Drive 1.

5 REM Drive 0
10 OUT 244,1: OUT 240,3
20 FOR T=1 TO 700: NEXT T
30 OUT 244,1: OUT 243,40: OUT 240,19
40 FOR T=1 TO 700: NEXT T: GOTO 10

5 REM Drive 1
10 OUT 244,2: OUT 240,3
20 FOR T=1 TO 700: NEXT T
30 OUT 244,2: OUT 243,40: OUT 240,19
40 FOR T=1 TO 700: NEXT T: GOTO 10


Larry
 
wow, this is fantastic!
Thanks so much Larry, I'll do these tests today and let you know what I get.
Yea, in hindsight, swapping the stepper motors was a really stupid idea, but I wanted to try to figure out if the stepper motor was the issue with drive 1. I thought that the best way to figure that out would be to take a known good working part... stupidly, I didn't even think that that might knock it out of alignment.
That being said, my main goal in working with these old machines is always to learn about them, and I feel like even when I don't get the results I want, or I do something stupid, I always end up learning something from the experience, so I'm not going to beat myself up too much.
 
just looked at my drives, they are Texas Peripherals from 1982.
In raised lettering on the bottom under the TP logo is what I'm assuming is the model number: 10-5355-001
 
ldkraemer said:
Looks like I have a couple of typo's in the code.

Now, step the head(s) from track 0 to 39 for Drive 0, then Drive 1.

5 REM Drive 0
10 OUT 244,1: OUT 240,3
20 FOR T=1 TO 700: NEXT T
30 OUT 244,1: OUT 243,40: OUT 240,19
40 FOR T=1 TO 700: NEXT T: GOTO 10

5 REM Drive 1
10 OUT 244,2: OUT 240,3
20 FOR T=1 TO 700: NEXT T
30 OUT 244,2: OUT 243,40: OUT 240,19
40 FOR T=1 TO 700: NEXT T: GOTO 10


Larry
Click to expand...
okay, ran the first set of tests, and both drives seemed to work exactly as they should. They both spun until I hit break on the first test, and they both moved from the outer to inner position and looped until I hit break.
One thing I noticed is that you said that drive zero is the top drive, but that isn't my understanding. It was my understanding that drive zero was the bottom drive. That's also how the tests went. When I was testing drive zero, the bottom one was the active drive, and when I was testing drive one, the top one was active. Maybe that was just a typo on your part?
Anyway, would I be correct in assuming then that both of these drives work fine, and they just need alignment?
I have another drive coming in the mail on Saturday, so maybe I can boot from that drive and use it to align the other two?
If not, can you give me any advice as to how I can get these drives aligned? (assuming that is all that is wrong here)
Again, thanks so much for your help,
Nate
 
Last edited:
Kilgoreroot,
Here are some links to aligning a floppy drive with no alignment floppy, by Terry Stewart.







I also have a Basic program for testing the Floppy Disk Controller (FDC) from within
basic. You could load it by cassette at 1500 baud. That will assure you the FDC is 100%
functional.

Larry
 
Nearly every Texas Peripherals and Tandon drive I own has had the setscrew on the stepper motor loosen up. Usually tightening the screw cures the problem, but for some odd reason, I've had to loosen it again and rotate the hub slightly and it works great after that. Just for the heck of it, give that a try.

I use Floppy Doctor and a scope to align my drives. It reminds me of converging a color CRT; a time consuming pain, but you feel good about yourself when you get it perfect. :)
I'd love to get a cat's eye disk, but that'll probably never happen as they can't be copied.
 
ldkraemer said:
Kilgoreroot,
Here are some links to aligning a floppy drive with no alignment floppy, by Terry Stewart.







I also have a Basic program for testing the Floppy Disk Controller (FDC) from within
basic. You could load it by cassette at 1500 baud. That will assure you the FDC is 100%
functional.

Larry
Click to expand...
Hi Larry,
So I actually found that Terry Stewart page just by googling around earlier, and using that as a guide I made some progress today. I got to the point where drive zero will boot 4 of the six trs80 disks I have perfectly, however, 2 of them won't boot at all, and I'm actually wondering if I may have damaged them in some way during the testing process (which would be a huge bummer because one of them has floppy doctor on it, and would be really useful for working on drive one)
As for drive one, I haven't had the same luck with it. It seems to just refuse to align properly. I'll take a look at the other links you gave me, and see if anything there gives me any ideas. It does appear to be just an allignment problem though because it will boot from disks that it has itself written, just no others.
I'll put some more time into it tomorrow. If all else fails, I'll just replace it. Hopefully I'll get it figured out soon so I can put everything back together because it's incredibly obnoxious using this machine with the screen sitting sideways next to it.
 
Torch said:
Nearly every Texas Peripherals and Tandon drive I own has had the setscrew on the stepper motor loosen up. Usually tightening the screw cures the problem, but for some odd reason, I've had to loosen it again and rotate the hub slightly and it works great after that. Just for the heck of it, give that a try.

I use Floppy Doctor and a scope to align my drives. It reminds me of converging a color CRT; a time consuming pain, but you feel good about yourself when you get it perfect. :)
I'd love to get a cat's eye disk, but that'll probably never happen as they can't be copied.
Click to expand...
So the stepper motor is pretty secure, but I'll give the hub rotation trick a try. Thanks for the tip!
 
Kilgoreroot,
DITTO for what Torch has already stated. The problem of the track 0 adjustment is because the HUB that
attaches to stepper shaft has slipped a bit, or in your case loosened, and not tightened back in the exact spot.

Most folks rush to the alignment screws, but if the HUB is repositioned back to the correct position on the
stepper motor, and the drive is stepped to track 16, the CATS EYE Pattern will be located. And, if the
alignment is once again correct (without adjusting it), all that needs to be checked is the Track 0 Switch
changing voltage between tracks 3 and 2 before moving to Track 0. Here is the excerpt from the Manual.

Verify the Track 00 Switch (S2) adjustment by setting the
head on track 03 and checking for +5.0V at pin 1 of Connector
P11, then step the head to track 02, the reading at pin 1
of P11 should be OV.
Click to expand...

But, it isn't an easy job, and will take some time.

I'll gather the FDC test program and Floppy Doctor so you have those tools handy.
I also have a Diagnostic testing floppy.


Larry
 
Kilgoreroot,
YES, TPI Floppy Drives. The Latest Model 4 Manual has a lot of information on this drive. It is a cheap
copy of the Tandon TM-100 series. I'll add that manual to the others I put on PCloud for you, in the next
few days. I'm still gathering files and trying to catch up with other work.

Floppy Doctor 3.2B is the latest copy I have located.

If you have TRSTOOLS you can add files to your TRSDOS Images.


I asked my Brother which Drive was ZERO, because he had a Model 3 and Model 4. He may have given me
the wrong information, as I seemed to remember the lower floppy being Drive 0. On my Kaypro it is the TOP
drive.

Larry
 
ldkraemer said:
Kilgoreroot,
YES, TPI Floppy Drives. The Latest Model 4 Manual has a lot of information on this drive. It is a cheap
copy of the Tandon TM-100 series. I'll add that manual to the others I put on PCloud for you, in the next
few days. I'm still gathering files and trying to catch up with other work.

Floppy Doctor 3.2B is the latest copy I have located.

If you have TRSTOOLS you can add files to your TRSDOS Images.


I asked my Brother which Drive was ZERO, because he had a Model 3 and Model 4. He may have given me
the wrong information, as I seemed to remember the lower floppy being Drive 0. On my Kaypro it is the TOP
drive.

Larry
Click to expand...
Thanks so much for your help Larry, I'm going to put some time into this tomorrow.
 
kilgoreroot,
I've OCR'd pages 7 thru 12 of the SAMS Photofacts for the Model 3. I'm proof reading those
OCR'd pages during spare time in the evenings. I have an idea about using Track 16 with
sectors filled with 0x2F to get a 125KHz signal that will be written to Track 16. That way
you will have an idea how to properly locate Track 16.

More a bit later after I do a bit of testing.

Rough draft:
Code: 
 To check a pre-written floppy for the position of Track 16,
 (Cats-Eye Pattern on Dysan 224/2A Floppy) we can use the read
 circuit's information to assist in positioning the head carriage
 assembly by adjusting where the hub is located on the stepper motor's
 shaft.
 
 NOTE: This will get the Hub close to the original position on the
 stepper Motor's shaft.
 
 Type in and run the following Basic program.  Insert your
 pre-written floppy with 0x2F written on every Sector of Track
 16 into the Disk Drive and close the door.  The program will
 turn "ON" Drive 1, set the head to track 16, continuously read
 the track and display the number that is read, which should be 255.
 To turn "ON" Drive 0, change OUT 244,2 in lines 10 and 30 to OUT 244,1.
 Press the Break key to stop the program.
  
 10 OUT 244,2: OUT 240,3    REM Select Drive 1 = 2, or Drive 0 = 1, Step Rate 30ms 
 20 GOSUB 50            REM Wait
 30 OUT 244,2: OUT 240,228    REM Select 2 or 1, OUT 0xF0 1110 0100 Read Track w/15ms delay
 40 PRINT "TRACK ";INP (241)  INP(243): GOSUB 60: GOTO 30        REM Print Track Number and Data that was read
 50 REM                REM may be BUGS as I'm no assembly or basic programmer.  Make it slow to update.
 60 F0R T=1 T0 600: NEXT T : RETURN    
 
 The waveform should change from random pulses when the Drive door
 is open to 125kHz pulses (See Figure 8) when the Drive door is closed.
 NOTE: The random pulses are present in the Read circuits from pin 7 of
 IC 5B to pin 5 of IC 5E even when the drive is not running.  If the
 waveform does not change from random pulses with the Drive door open
 to 125kHz pulses with the Drive door closed or the pulses are missing
 readjust the position of the head by loosening the Hub's setscrew and
 fine tune the Head Carriage Assembly's position for Track 16.  It should
 be close to 2.54321 inches?????? (Just a Guess, until I measure it,
and test this code on my Model 4.)


Larry
 
I have always aligned with a good floppy, allowed the head to step to track zero then with the scope on the output of the head amp, adjusted the position to get the strongest peak on the waveform.

If your track zero is so far out its not actually on track zero then adjust and repeat. Some drives (all 5.25's maybe ?) will complete steps to a full phase on the stepper after they see track 0 switch made so its important to let the head step to zero rather than moving it by hand (as you might move it to a 1/2 step, align it only to find when the machine steps the head, its no longer aligned)
 
Killgoreroot,
I've created a TRSDOS Ver 1.3 M3 Image that can be used to setup your Head Carriage Assembly.
The image has 40 Tracks, 18 Sectors per track and 256 Bytes per sector.

Tracks 3 and 16 have hex bytes of 0x2F to fill these two tracks.

Track 16 is where the typical CATS-EYE Pattern is located.

Track 3 is where the Track 0 Detector starts changing state so it has changed by the time Track 2
has been passed.

I just need to write the Image to floppy, then read with Imagedisk and my GreaseWeazle.


Larry
 

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Sorry I can't help, but this brings back memories of my six months in the computer repair shop (back in 1986) for the Los Angeles Unified School District, where I learned to align a floppy drive with a head-positioning utility, an analog alignment disk, and an oscilloscope.

It's been too long since I've done it, for me to be of any help, but I will say that I found Tandon and TPI drives much easier to deal with than Schugart or Alps drives (or any of the other 5 1/4 suppliers Apple used; as I recall, the Tandon and TPI drives had a little cam with a screwdriver slot, that would allow you fairly fine control over the position of the stepper motor, whereas the other manufacturers provided no such fine control.
 
I've created three Double Density, 40 Track, 18 sectors per track, 256 bytes per sector images
with the 0x2F pattern at Track 3 and 16.

The t3dt16.dsk image is TRSDOS Ver 1.3 for TRS-80 Model 3. It has 40 Tracks, Double Density,
18 Sectors per track and 256 bytes per sector.

The n3dt16.dsk image is NEWDOS-80 V2 for TRS-80 Model 3. It has 40 Tracks, Double Density,
18 Sectors per track and 256 bytes per sector.

The l3d5316.dsk image is LDOS V5.31 for TRS-80 Model 3. It has 40 Tracks, Double Density,
18 Sectors per track and 512 bytes per sector.

Tracks 3 and 16 are filled with 0x2F.

Track 3 is where the Track 0 Detector starts changing state and has changed state
after the head carriage assembly is heading for track 0.

Track 16 is where the typical "CATS-EYE Pattern" is positioned on the Dysan Alignment floppy.

Larry
 

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