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Tandon TM-100-2A failture

romanon

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Oct 1, 2013
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Slovakia
Hello, i have one Tandon FDD, it is tested drive with sometime confirmation of service, but i dont know why, its not working properly.
I cant boot from this floppy drive, but i can read directory structure. Also formating is ended with strange error. Any help?

WhatsApp Image 2018-11-20 at 20.19.13.jpg s-l1600 (6).jpg IMG_7624.jpg
 
Does it make the "click" sound when it searches the disk? There's a small vertical switch in the back end of the rail and when the head moves the switch always goes on&off (spring loaded upwards with audible "click" sound) determining the place of the head. Once the switch was dirty enough it didn't click upwards anymore and the head was trying to reverse against the edge and confused the reading/writing process hence it caused such weird errors.
 
It looks as if you are using the Drive on a DOS computer. Does your floppy cable have a twist in the cable. Is there another floppy on the cable?
Is the Tandon TM-100 on the Middle or last connector of the Floppy cable.

Check Posting #4 here: http://www.vcfed.org/forum/showthre...C-Formatting-problems&highlight=Tandon+TM-100

The Terminator is used for the last floppy on the END of the Cable. If your DOS Computer already has a floppy on the middle connector, your
Tandon TM-100 will be on the End of the cable with the Terminator Installed and also strapped for DS1.


Here are a few important things I do to my 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 .001 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.

2. 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. Make sure the heads
glide easily for the full length of the Drive Guide Rails. Same method works on Flat Bed Scanners.
www.drislide.com/

3. 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.)

4. 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.


Larry
 
It seems that the head rails aren't the only place where old lube can cause trouble. I have had several of these drives that exhibit sporadic operation respond to a little WD-40 around the spindle of the stepper motor.

I set the drive on it's side so the WD can soak in downward, then after a little while I flip the drive over and do the same thing to the other side of the stepper motor. I access the "inner" side by temporarily removing the clear plastic guard on the TM-100. This is something that has helped other brands of floppy and hard drives that have that old style stepper motor, though you can really only access one side of the stepper on hard drives.

From your photos it appears there is no terminator installed on your drive. Your photos also show the drive installed as "A:" drive. It will need a terminator installed to work properly.
 
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Drive is lubricated well, heads are moving lightly without any problem. I also cleaned RW heads with IPA. Terminator is installed.
 
One more thing..Drive came with very strange drive selector

46482080_372562203488874_5606354762908827648_n.jpg

I dont understand this option...

So I replaced it with classic DS1 connector

46391919_2735075736717524_5617550359670030336_n.jpg

but nothing has changed
 
So I tested TOP and also rear PCB with another working tandon drive and its working. So we can exclude PCB's errors.
 
Since you know it has to be some physical part on the Drive it's self, I'd start by looking at the Floppy Door Hinge.
If you look at the Hinge points, does it have two small white Nylon pins, versus one long Brass Rod for the Hinge
Rod? If so, you need to look over that hinge part, because one side will break (or crack) and that won't keep the
door closed properly. You should be able to feel a difference in the way the door closes with a broken hinge part.
(There are drawings and CAD files on Thing-I-Verse for 3D printing that part.......I'm the one that posted that information.)

If the hinge looks good, then double check the two read Head cables and connectors that attach to the Logic PCB).
There isn't much else to check unless your Track 0 switch isn't working properly. You can verify that with a Voltmeter.
You should hear it click as the switch makes. Double check that it is actually switching with a Voltmeter.

It would be interesting to take a data disk, and try to format it in the Defective floppy and see if it Writes as it formats, but
just doesn't read. Perhaps, it doesn't write as well as not reading? That would tell you more about where the problem
could be located. Then you could actually see if anything gets written to some of the sectors during Format with your DOS
Software.

Larry
 
It's beginning to sound like a Read Head problem, after looking at the Schematics. I've located the OHM values for all
the Heads. That should make it easy for you to verify the heads are good.

TM-100-HEADS.jpg


There is some information I can send you with some software that will help you test the Read operation.

The following Basic program will make Disk Drive B run continuously in the read mode with HEAD 0 ON.
To make Disk Drive A run continuously, in line number 80 change the number 37 (2nd number) to number 20.
Code:
10 DEF SEG=0
20 DEF USR=40000
30 FOR X=40000 TO 40007
40 READ Y
50 POKE X,Y
60 NEXT X
70 A = USR(O)
80 DATA 176,37,186,242,3,238,235,253


Type in and run the program given in the "Direct Operation of Disk Drive" section of this Troubleshooting guide to
make the Disk Drive run continuously in the read mode. To verify that the Disk Drive is operating in the read mode,
check for a low logic reading at pin 10 of IC 2B.

If the reading at pin 10 of IC 2B is not low, check for a high logic reading at pin 11 of IC 2B. If the reading is
high, check IC 2B by substitution. If the reading is not high, check for a low logic reading at pin 13 of IC 3B.
If the reading is low and the logic reading is high at pins 9, 10 and 12 of IC 3B, check IC 3B by substitution.
If pin 13 of IC 3B does not read low, check for a high logic reading at pin 13 of IC 3D. If the reading is high,
check IC 3D by substitution. If the reading is not high, check the cable and connectors going to the Disk Drive
Adapter. If the cables and connectors are normal, check for a low logic reading at pin 15 of Driver IC U7.
If the reading is low, check IC U7 by substitution If the reading is not low, check Control IC U6 by substitution.

If the reading at pin 10 of IC 2B is low put a diskette into the Disk Drive and close the Disk Drive door. The diskette
should be filled with programs to insure that the head will continually read information. Check the waveforms at pins
1 and 14 of Diff Amp IC 4A. If the waveforms are missing, check the voltages and components associated with pins 1,
4, 5, 7, 8, 10, 11 and 14 of Diff Amp IC 3A. Check Diodes CR2, CR3, CR11, CR12 and the resistance of the heads.
A problem in the head switching circuit, Switching Transistors Q6 & Q8, may affect the read circuits. If the problem
appears to be in the head switching circuit, see the "Disk Drive Will Not Switch Sides" section of this Troubleshoot·
ing guide. If the waveforms are good at pins 1 and 14 of IC 4A, check the waveforms at pins 2 and 3 of IC 5B. If the
waveforms are missing, check the voltages and components associated with pins 4,5,7,8,10 and 11 of IC 4A. If the
waveforms are normal, check the waveform at pin 7 of IC 5B while opening and closing the Disk Drive door. A noticeable
shift in the waveform pulses should occur. If no change occurs, check IC 5B by substitution.

NOTE: The waveforms shown at pin 12 of IC 5D and pin 4 of Multivibrator IC 5E should be present even when the disk
drive is not running. If the waveforms are missing, check Capacitor C11 and Resistor R22 and check Multivibrator IC
5C and IC's 5D and 5E by substitution. If the waveforms are normal, check the waveform at pin 5 of IC 5E. If the
waveform is missing and there are pu1ses at pin 1O of IC 5E, check Capacitors C12 and Resistor R24 and check IC 5E
by substitution. If the waveform is present, check for pulses at pin 8 of IC 1F. If the pulses are missing and the
logic reading is high at pin 10 of IC 1F, check IC 1F by substitution.


Larry
 
Here is a bit more explanation on the above Basic code. The Basic program assumes the standard PRIMARY
Floppy Port of 0x03F0 thru 0x03F7. But, if your DOS Computer uses the SECONDARY Floppy Port of 0x0270,
you will need to change the program accordingly. Also, those PORTS can likely handle Floppy's A:=Drive 0,
B:=Drive 1, C:=Drive2, and D:=Drive 3. If that is the case, then you also need to change the Data that is sent
out the DOR (Digital Output Register = Base Port +2) to the Floppy Drive. All of this information is contained
at this URL:

http://viralpatel.net/taj/tutorial/programming_fdc.php#Digital_Output_Register

A: = 20 = 0x14
B: = 37 = 0x25
C: = 70 = 0x46
D: = 135 = 0x87

Basically the program is:
Code:
........mov al,floppynumber
........mov dx,portnumber
loop:
........out dx,al
........jmp loop
Code:
........mov al,14h
........mov dx,03f2h
loop:
........out dx,al
........jmp loop

This will put the Floppy Drive in READ Mode, so further testing can be done on the READ circuits.

Don't overlook the Track 0 switch, and make sure you VERIFY it is switching HIGH and LOW according
to where the Head carriage is located. If it's not switching, or not switching properly the READS will be
incorrect.

Another thing you might want to VERIFY is that both Logic PCB's are using the same OHM value Terminators.
Most likely they are 150 OHM as per print, but Chuck(G) has posted somewhere on the VCF about using 1K OHM
Terminators because some Motherboards can't sink the 150 OHM ones properly.


Larry
 
Check that the capstan that drives the heads is not slipping on the stepper motor shaft.

I've had TM100's with loose capstans which 'sort of' worked; however they slipped occasionally which resulted in random errors.

After you have done that I would do a full realignment. You can do it without special disks and a scope; you just need an OEM floppy with something on it (i.e. windows disk, dos disk etc), Dave Dunfields Imagedisk (see here) and a lot of patience....
 
I seem to have a typo in the Secondary Floppy Drive Port. It is 0x0370, not 0x0270. If I was able to edit my posting I could have corrected it.

It could be a loose Coupling for the Taunt Band that positions the head carriage assembly, as I have also seen that. It would be easy
to check, and then try to format a floppy again.

Larry
 
Check that the capstan that drives the heads is not slipping on the stepper motor shaft.

I've had TM100's with loose capstans which 'sort of' worked; however they slipped occasionally which resulted in random errors.

After you have done that I would do a full realignment. You can do it without special disks and a scope; you just need an OEM floppy with something on it (i.e. windows disk, dos disk etc), Dave Dunfields Imagedisk (see here) and a lot of patience....

exactly this!^^^^^^

I have had several Tandons and Texas Peripherals with that loose setscrew causing slippage and now it's the very first thing I check. I didn't even realize it at first...just when I thought I had all aligned using my scope, it would be off again ranging from just a few minutes to a weeks worth of use. Had me pulling my hair out.
Read about the capstan issue, checked mine and sure enough that was it. 4 different drives all had set screws that needed to be tightened.
 
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There is not alignment error as for me. I very tried this floppy drive to resurrect and once normally booted from the floppy disk, in other case, refuse to read DIR, also formatting... once good, other case with errors...
 
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