Repairing a TM-100 drive

[Tiny_Bob]

I recently got a 5160 XT, and the disk drive is giving me some problems. When it attempts to move the head, it just shutters around and doesn't move, resulting in a 601 error. I have tried 3 different motors, all showing the same symptoms. The attached video shows the drive in action. I have use some oil on the original motor bearings, and the 2 replacements I bought feel alright. I'm worried its a logic board problem, and if that's the case I have no idea where to start troubleshooting. Any ideas?

 

[syzygy]

Make sure your linkage is intact, - look here at a drive that I bought cheaply that had a severed ribbon on the linkage. I now have a spare parts drive. Not saying that is what's going on with yours, just saying it is something to check.

 

[Tiny_Bob]

Ill check that in a few. I should also mention that the motor does this without being connected to the transport assembly. The shaft of the motor itself is vibrating too.

 

[syzygy]

So, there is the drive motor and the stepper and the linkage so the stepper can move the head. Which have you replaced three times? Does the drive motor spin the diskette when was is inserted?

 

[Tiny_Bob]

the diskette does spin up, its just the head stepper that has problems. i have tried 3 different stepper motors, all 3 have the vibration problem

 

[Reynold1]

Was the drive ever dropped that you know of? Something could slightly be bent enough to cause it to not move properly.

Also I would check for cracked/broken solder joints where all the connections on the logic board are for the cables, as well as the small board on the back of the drive where you can adjust the speed. I have had broken joints on that board specifically, the small rear one, that threw me for a loop on drives before.

 

[syzygy]

the diskette does spin up, its just the head stepper that has problems. i have tried 3 different stepper motors, all 3 have the vibration problem

Ok. I would have a look at the linkage and if intact, the logic board. Lots of others on here with much more knowledge that can weigh in

BTW: do you have this?

 

[Tiny_Bob]

i did not have that manual. ill take a look through it and see what i can give me. thanks!

 

[Tiny_Bob]

And just looked at the linkage and its fine

 

[syzygy]

And just looked at the linkage and its fine

i have tried 3 different stepper motors, all 3 have the vibration problem - with no linkage problem, that result suggests that the logic is not providing the pulse that the stepper wants (or something else

ok, good luck...welcome to the site...and let us know how it goes.

 

[Tiny_Bob]

Thanks ya for the help so far! This is my first dive into a truly old system like this.

 

[Mochatea396]

I didn’t see it mentioned but does the head move freely on the rails? You should be able to slide it along the rails with your fingers. Sitting for many years the head can get stuck. I’ve had a head assembly stuck. Alcohol on the rails and slide the head back and forth a few times to make sure it’s free.

 

[modem7]

Single TM-100. Is the drive terminated? See the 'Incorrect termination' section of [here].

 

[ldkraemer]

I have used the Motorcycle Cable Lubricant "Dri-Slide" for years on my Floppy Drives. After wiping
the Head Carriage Drive Rails with an Alcohol Dipped Cotton Swab, and a few minutes drying, I
drop about three drops along each rail. Then EASILY slide the Head Carriage Assemble full
travel a few times. This lasts for Years. Also works well on Scanner Rails

Dri-Slide can be purchased at about ANY Motorcycle Shop or Walmart. One Can odfDri-Slide
lasts years.


Larry

 

[Tiny_Bob]

Was the drive ever dropped that you know of? Something could slightly be bent enough to cause it to not move properly.

Also I would check for cracked/broken solder joints where all the connections on the logic board are for the cables, as well as the small board on the back of the drive where you can adjust the speed. I have had broken joints on that board specifically, the small rear one, that threw me for a loop on drives before.

not that i know of, the rest of the computer is in decent shape. it was exposed to moisture at some point in its life, no surprise since it was in Florida.

I didn’t see it mentioned but does the head move freely on the rails? You should be able to slide it along the rails with your fingers. Sitting for many years the head can get stuck. I’ve had a head assembly stuck. Alcohol on the rails and slide the head back and forth a few times to make sure it’s free.

Yeah, i have cleaned and lubricated the rails with some 3-1 oil, and the whole assembly moves super easy when the stepper is not installed.

Single TM-100. Is the drive terminated? See the 'Incorrect termination' section of [here].

I've looked at this section before, but didn't quite understand it, but ill take another look.

 

[ldkraemer]

You need the proper Drive Select Set, and the PULLUP resistor for a Single Drive, or for the last Drive on the cable.

If you are connecting to a non CP/M computer with a Twisted Cable with conductors 10 thru 16 Twisted, both
Drives need to be strapped for DS1 in a DS{0..3} configuration, or DS2 in a DS{1..4} configuration. This all
depends on how the Drives are Marked.


Larry

 

[Tiny_Bob]

1E has a jumper for DS1, but thats it. 2F is completely empty...

 

[Tiny_Bob]

ok after some guidance from Larry (thanks so much), I've started to probe the drive with a scope. Pins 1, 2, and 4 of P12 look ok, with the only oddity is Pin 1 is pulled low at powerup. Pin 3 has a waveform much different from the others. ill attach images from my scope.

 

[ldkraemer]

I'd check the Inputs of the Drivers as well as the outputs. And don't forget the Diodes that are also
in the circuit and can be shorted.

I have attached the DS75462 Datasheet and the Schematic of the Stepper Circuit. Shouldn't take long
to check the Diodes front to back with power off and then probe the IC Inputs and Outputs.

OH! be sure to have a look at the back side of the Logic Board, as you could just have a cold solder Joint.
I ran across that on one of my TRS-80 Model 1 Aerocomp Drives 40+ years ago. Took a while to locate it.

Larry

 

[Tiny_Bob]

I probed both driver ICs and recorded the results on this diagram. So all the inputs match, but pin 8 of IC 4D (which goes to pin 3 of P12) has the non square wave that i measured on P12. does this mean that 4D is bad?