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Tandon TM-100 alignment woes

ef1j95

ef1j95

Experienced Member
Joined
Oct 10, 2013
Messages
145
Location
Philly, Yo
I have what appears to be typical problems with a Tandon TM-100-1A. The drive :)1) is reading / writing fine, but can't read disks made with the other drive :)0). I had it working briefly by adjusting the radial alignment using the Avery / Tezza method (http://www.classic-computers.org.nz/blog/2010-06-28-alignment-tandon-m100.htm) but it stopped working again and I've had no luck getting it back into alignment.

(1) It seems that I can't quite back the head up to fully align with track 00 written by drive :0. The cam screw is at its maximum displacement. I'm guessing this has to do with the track 00 sensor, but other than the Tandon / Radio Shack / SAMS data sheets, I haven't seen any info on making this adjustment.

(2) Also somewhat confounding is that this is the TM-100 model with combined servo and controller boards. Does anyone have tech info on this model? My Google powers have failed. The test points on the board are different than those documented in the Tandon and SAMS sheets that have separate controller and servo boards. The Model III service manual at least has a schematic of the combined board, but no info on which TP's to use in the alignment (I'm guessing TP 2, 3).

Eric
 
There are a couple of important things I do before actually aligning the Tandon TM-100 drives.

1. The frst versions of the TM-100's used a Brass Pin across the full length of the Door as the Hinge Pivot. Later Versions used two small White (plastic or nylon pins) which don't
work as quite as well as the initial versions longer Brass Pin. I've used my Dial Caliper to get some .003 oversized Brass Brazing Rod to make replacement
Hinge Pins so the door hinge closes easily and consistent. If the door doesn't feel right when you close it, check for loose/missing white pins.

I'm also assuming you still have the Original Tandon TM-100 Full Height Drives in the Model 3. Is that correct? With power off the Model 3, slip a floppy into the first drive.
Carefully close the drive latch. See if it feels normal and then slowly open the latch. Repeat for second drive. Both should feel the same. What you are looking for is the
pins the door pivots on in the latch. Later production drives were modified to use two White Nylon Pins, versus one one long, solid brass pin across the latch. You will know
from the feel of the latch when closing it, if it's a problem. The White Nylon pins don't let the Head assemble load onto the floppy properly. I use a piece of Brass Brazing
Rod (the largest oversized rod .002 or .003) from my Welding Supply house to cut new full length Piviot Pins and slip them into the drive latch. That has fixed my problem
for sure on several machines. The Brass Rods are 1/8" if I remember correctly. I just carried my Micrometer and looked through their stash for the largest oversize that I
thought would fit the latch.

Another thing you need to do is to get some Dry Slide which is a Motorcycle product for lubrication of cables, and carbs. It doesn't attract dirt, and works well to lubricate
Drive and Scanner rails. A few drops goes a long way, after shaking the can to mix the lubricant. I clean the rails the best I can with a cotton swabb dipped in Alcohol.
Then drop a few drops of Dry Slide on the Drive Rails. I then carefully cycle the rails from end to end. You will notice a lot less effort to move the head assembly.
Same method works on Flat Bed Scanners.
www.drislide.com/
Click to expand...

2. Before starting to Align the Drive do the Following:
Clean the Drive Head(s) with a Q-Tip dipped in Alcohol, making sure it's clean. (Remove the Head Cables from the Circuit Board and swing it out of the way.)
Clean the Drive Guide Rails with a Q-Tip dipped in Alcohol.
Lubricate the Drive Guide Rails with a few drops of Dri-Slide (Motorcycle Cable Lubricant that doesn't attract dirt).
Make sure the heads glide easily for the full length of the Drive Guide Rails.
Set RPM Speed of Drive Spindle to 300 RPM with Disk Inserted and spinning in drive.
Step the Head carriage across all tracks making sure it steps easily, and doesn't make a lot of thumping as it steps.
Use a Magnet to ERASE a TEST Floppy so you know all the Tracks were written by the drive being tested.

3. Track 0 likely needs to be set too.

Larry
 
Last edited:
Thanks for the tips! These are the full height drives.

I'm going to go back to clean and re-lube the rails. It is thumping a bit more with track changes than the other drive. Heads were cleaned recently, and I've checked out the drive door. Looks ok so far. Verified the speed, too.

I'm going to give it a shot setting track 0 next, then readjusting the radial alignment. That alignment cam screw is pretty rough.
 
ef1j91 said:
(2) Also somewhat confounding is that this is the TM-100 model with combined servo and controller boards. Does anyone have tech info on this model? My Google powers have failed. The test points on the board are different than those documented in the Tandon and SAMS sheets that have separate controller and servo boards. The Model III service manual at least has a schematic of the combined board, but no info on which TP's to use in the alignment (I'm guessing TP 2, 3).
Click to expand...

I commiserate with you on this. I also have some of those newer board TM-100-1 drives. The only documentation I could ever find on the new combined logic board was in the later Model III tech manual. Even the Tandon manual from 1983 does not mention it. AFAIK, testing docs on that board do not exist. Enough has changed on that new board that the only way to test it is to really dive into the schematics and understand it at a low level. I haven't dedicated the time yet, but maybe someone else has? However, after a quick look I think TP2 and TP3 are a good starting point.
 
Here are the Test Points for the New Circuit Board.

TP1, TP4 = GND
TP2, TP3 = HEAD READ SIGNALS
TP5 = N TRK 00
TP6 = STEP
TP7 = N READ DATA
TP8 = WRITE-PROT
TP9 = N INDEX
TP10 = DIR
TP11 = N MOTOR

SHUNT JUMPER OR DIP SWITCH (CLOSED)
Drive Select 0 = NDS1 J2 Pin 10
Drive Select 1 = NDS2 J2 Pin 12
Drive Select 2 = NDS3 J2 Pin 14
Drive Select 3 = NDS4 J2 Pin 32

Larry
 
pski said:
I commiserate with you on this. I also have some of those newer board TM-100-1 drives. The only documentation I could ever find on the new combined logic board was in the later Model III tech manual. Even the Tandon manual from 1983 does not mention it. AFAIK, testing docs on that board do not exist.
Click to expand...

Which "later Model III tech manual" did you look at? Perhaps it wasn't late enough. The Model III Technical Reference Manual (26-2109) with the October 1981 date on the back ("1081") includes a twenty-page "Supplement to Section IX" with pretty complete documentation on the new single-board drives. See pages 123-142, here:

https://archive.org/stream/Model_III_Technical_Reference_Manual_1981_Tandy#page/n133/mode/2up
 
Got the drive working again by readjusting the radial tracking. Thanks for the great tips and advice. The test points for the new board drives are very helpful.
 
Well... after having it running most of the afternoon now both drive motors won't spin up. The disk access lights comes on, but neither motor spins. Voltages look ok coming in (5V and 12V) and I switched the drives, tried operating with only one, etc.

Sheesh.
 
Petrofsky said:
Which "later Model III tech manual" did you look at? Perhaps it wasn't late enough. The Model III Technical Reference Manual (26-2109) with the October 1981 date on the back ("1081") includes a twenty-page "Supplement to Section IX" with pretty complete documentation on the new single-board drives. See pages 123-142, here:

https://archive.org/stream/Model_III_Technical_Reference_Manual_1981_Tandy#page/n133/mode/2up
Click to expand...

Ah, you can never be thorough enough! I had that version printed out but the supplement somehow went missing.

Thanks much, Pretofsky!
 
Just a thought, but are you sure that the hub for the head carriage band attached to the head stepper motor is tight? I am in the process of troubleshooting my Commodore 128D's drive and saw that mentioned in a Commodore disk drive repair manual that on some 1541 drives this hub wasn't keyed to fit one way and could slip on the spindle of the motor. Since you say you have moved the adjustment all the way to the bump stop.
 
geoffm3---Great tip. I did check the carriage band for slip (recommended on Tezza's page). It appears to be holding well.

My thanks to Pretofsky also for the later MIII reference manual, too. Now if I could only get the motors to spin... will focus on verifying (1) power to board and (2) mechanical for now.
 
To get the Spindle Motors to run on the Drives you really only need +5 VDC, +12 VDC, Terminator Resistor RP1 inserted in Last Drive on Cable, and N MOTOR (J2-Pin 16)
pulled LOW. (This LOW at U12 Pin 3, will be inverted to a HIGH on TP11, and enable Logic for MOTOR PWR, as shown on the schematics.)

You can test each drive by inserting a Terminator Resistor (RP1), then connecting the Power Molex Plug, and pulling N MOTOR (J2-Pin 16) LOW with a Jumper. The spindle
should spin.


Larry
 
ldkraemer said:
To get the Spindle Motors to run on the Drives you really only need +5 VDC, +12 VDC, Terminator Resistor RP1 inserted in Last Drive on Cable, and N MOTOR (J2-Pin 16)
pulled LOW. (This LOW at U12 Pin 3, will be inverted to a HIGH on TP11, and enable Logic for MOTOR PWR, as shown on the schematics.)

You can test each drive by inserting a Terminator Resistor (RP1), then connecting the Power Molex Plug, and pulling N MOTOR (J2-Pin 16) LOW with a Jumper. The spindle
should spin.


Larry
Click to expand...

I will check it out and report back. The resistance and continuity across the spindle motor were ok based on the SAMS factsheet that's floating around (178 ohms across pins 1,2 continuity across pins 3,4). I am guessing that since both drives won't spin up, the drive PSU is the culprit.
 
Well it took a while, but I have both drives up and running again.

Ultimately, the PSU was ok. I played around with this a while but everything seemed fine. No bulging caps, V out were ok, and substitution with a Mean Well PSU I had lying around didn't change the behavior.

Next, I focused on the drive itself. Working through the electronics, I was able to verify that the board on my drive :0 seemed to be functioning properly (this is the single-board Tandon 100-A). As Larry says, there's a low into the U12 (a ULN2003AN) and this is inverted to a high (about 10V) that drives the motor electronics. Both transistors Q7 and Q8 seemed to be fine. This was confirmed when I plugged the good drive's motor into the :0 board and it spun up. So the motor itself was out of commission.

Ultimately, lubricating the motor restored it to proper function. I got to this by a round-about way of partially disassembling it, which, while educational, is not something I recommend. I do think that lubricating both the spindle axle and the axle under the blue plastic cap on this motor was ultimately important.

Just after this, my drive :1 started acting up (not spinning). Lubricating the motor (while NOT disassembling it, natch) restored it, too. So, I guess I have some gumming up of motors on my hands. I wonder if this is typical of the Tandons or a result of previous maintenance?
 
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