Tandon TM100-2

Tandon TM100-2
Tandon TM100-2A (photo: Mister rf, CC BY-SA 4.0)
Manufacturer	Tandon Corporation
Type	Full-height 5.25-inch floppy disk drive, double-sided, 48 TPI
Interface	34-pin edge connector; 4-pin AMP power connector
Compatible	IBM PC (5150), IBM 5155, IBM PC XT (5160)
Dimensions	86 x 149 x 203 mm (IBM)
Weight	2.04 kg (IBM)
Predecessor	Tandon TM100-1
Model	TM100-2, TM100-2A
Storage	500 KB unformatted; 320 KB under DOS 1.1, 360 KB under DOS 2.0 and later
Media	5.25-inch double-sided double-density soft-sectored diskette, 40 tracks per side

The Tandon TM100-2 is a full-height 5.25-inch double-sided floppy disk drive with 40 tracks per side at 48 tracks per inch. It is the two-head version of the Tandon TM100-1, and Tandon documents both in one manual. It was used as the "360K" drive in the IBM PC (5150), the IBM 5155 Portable and the IBM PC XT (5160); a later version is marked TM100-2A. IBM first called it the "320 KB Diskette Drive", because DOS 1.1 formats 8 sectors per track; DOS 2.0 and later format 9 sectors per track, giving 360 KB.

Specifications

Tandon TM100-2 specifications

Parameter	Value
Heads	2
Tracks	80, 40 per side, at 48 TPI
Track spacing	0.529 mm (20.8 mil)
Unformatted capacity	500 KB per disk
Recording modes	FM, MFM, MMFM
Data transfer rate	250,000 bit/s, double density
Flux reversals per inch, inside track	5,535 side 0; 5,877 side 1
Rotational speed	300 RPM ± 1.5 % (295.5 to 304.5 RPM)
Instantaneous speed variation	± 3 %
Average rotational latency	100 ms
Motor start / stop time	250 ms / 150 ms maximum
Seek time, track to track	5 ms
Head settling time	15 ms
Average access time, including settling	75 ms
Head life	20,000 media contact hours
+12 V supply	± 0.6 V, 900 mA average, 100 mV peak-to-peak ripple
+5 V supply	± 0.25 V, 600 mA average, less than 100 mV peak-to-peak ripple
Hard error rate	1 in 1012 bits
Seek error rate	1 in 106 seeks
MTBF / MTTR	8,000 hours at 25 % duty cycle / 30 minutes
Operating temperature	10 °C to 46 °C
Operating humidity	20 % to 80 %, non-condensing

All figures are from Tandon's Tables 2-1 to 2-3, pp. 2-2 to 2-4. IBM's own reference for the drive it sold gives some looser figures: 6 ms track to track, 500 ms maximum start time, and ± 5 % on both supplies.

DC power enters on a four-pin AMP connector, J2: pin 1 +12 V, pin 2 +12 V return, pin 3 +5 V return, pin 4 +5 V. A 3/16-inch quick-disconnect lug takes the chassis ground from the controller, and Tandon says the chassis should be earthed for proper operation (p. 3-5).

Configuration and termination

Drive address and options are set by a programmable shunt (AMP 435704-7) in a DIP socket at location 1E on the logic board; its positions can be cut, or it can be replaced by a DIP switch (pp. 3-5 to 3-8, Figure 3-3).

Tandon TM100 option jumpers

Jumper	Function	Setting
DS0-DS3	Drive select	Cut all except the one that addresses this drive
MX	Multiplex: keeps the drive logic enabled at all times	Single-drive systems only; cut in multi-drive systems
HS, HM	Not used	Cut
W2, W3	Write flip-flop set and preset lines	W2 standard
W4, W5	Write-protect switch	W4 standard (write protect enabled)
RP1	Terminator resistor pack	Fitted in the last drive on the cable only

The IBM PC's floppy cable swaps the drive-select and motor-on lines between its two drive connectors, so both drives are jumpered alike and the cable decides which is A:. minuszerodegrees warns that some wrong termination arrangements cause faulty drive operation.

Common faults

The faults below are the ones minuszerodegrees lists for the drive in IBM machines. Before blaming the drive, substitute a known-good one to rule out the controller, the cable and dirty edge connectors.

Hardened rail lubricant

The lubricant on the rails the head carriage slides on hardens, and the carriage moves stiffly or not at all. With the power off, the carriage should slide freely by hand against slight resistance from the stepper motor. The site's author cleans the old lubricant off and re-lubricates with a silicone-based lubricant, grease or spray, which he and others have found satisfactory, and treats a clean and re-lube as worthwhile even when it does not cure the fault. Tandon's manual contains no lubrication instruction.

minuszerodegrees also records that some owners with a stepper motor that would not step properly freed it with WD-40.

Head contamination

Old disks whose oxide wipes off can leave a thick deposit on the heads. The minuszerodegrees author notes that a cleaning diskette may need 20 to 50 passes to clear it, and uses isopropyl alcohol on a cotton tip instead, taking care not to damage the heads; a thick layer has taken him a couple of minutes to remove. He warns that cleaning diskettes are abrasive, and that a drive cleaned after a bad disk will be fouled again if that disk goes straight back in. That is his practice, not Tandon's.

Drive overloads the host power supply

If a TM100-2A shorts the PC's supply, minuszerodegrees names the two tantalum capacitors C36 and C43, each 4.7 µF 16 V, as the first suspects. An aluminium electrolytic of the same value, or a 25 V part, will do as a replacement. Fit it with the positive lead in the hole marked "+". See Capacitor Failure Symptoms.

Spindle speed

The specification is 300 RPM ± 1.5 %, 295.5 to 304.5 RPM. Adjust R4 on the servo board at the rear of the drive. minuszerodegrees gives three ways to measure the speed: the frequency at pin 2 of the servo board's LM2917 on a digital oscilloscope; ImageDisk's Test RPM command; or the 50 Hz and 60 Hz strobe rings on the spindle flywheel under strong mains-powered fluorescent light, using the ring that matches the local mains frequency. It also records a speed fault cured by tightening a loose spindle flywheel screw, and suggests the spindle may need lubrication.

Track 0 switch

The TM100's Track 0 sensor is a mechanical switch, operated by the head carriage between tracks 0 and 3 (p. 4-3). minuszerodegrees quotes Chuck(G) of the VCFed forum: "I've found that many of the 'alignment' issues on Tandon 100s to be not alignment per se, but a dirty track 0 sensor." Check it before touching any alignment.

Bent test-point posts

The logic board's test points are upright posts. On a drive that has been badly stored or shipped, one may be bent over onto other circuitry.

Dirty hub clamp

minuszerodegrees links a case from the VCFed member Tezza in which a dirty hub clamp caused the fault.

Write-protect switch

If the drive treats every disk as write-protected, or none, check the switch (section 5.4, p. 5-3). With power off and a disk without a write-protect tab inserted, there should be continuity between the two wires of Plug 8; with a write-protected disk, none. Test Point 9 should be high for a write-protected disk and low otherwise; if the switch tests good and TP9 is wrong, suspect the logic board. The switch is moved up or down on its bracket to adjust it.

Head alignment

Alignment drift happens over many years but not on every drive. minuszerodegrees identifies it by two signs together: disks formatted in the drive read back in the same drive, but good disks formatted on a known-good drive will not read. The author advises against attempting an alignment without that evidence, because a failed attempt can leave the drive worse.

Alignment and adjustment

Tandon's checks need a dual-channel oscilloscope and a certified alignment diskette, Dysan 224/2A or equivalent. The alignment diskette and drive must stabilise at room temperature for one hour first (p. 5-6).

Tandon TM100 checks and tolerances

Check	Tolerance	Adjustment	Manual
Drive motor speed	300 RPM ± 1.5 %; the 60 Hz ring of the speed disk on the spindle pulley stands still under fluorescent light	R4 on the servo board	pp. 5-3 to 5-5
Radial track alignment	Cat's eye at track 16 on each head: smaller lobe not less than 75 % of the larger. Track 16 is 1.9167 in from the hub centre	Head module retaining and cam screws	pp. 5-6 to 5-9
Index to data	200 ± 100 µs	Index sensor retaining screw	pp. 5-9 to 5-10
Head azimuth	Within ± 18 minutes on the third burst at track 34, each head	Not adjustable: replace the module assembly	p. 5-11
Track 0 switch and stop	As described	Switch position; stop	pp. 5-12 to 5-13
Head output, cone centring	As described	Check only	pp. 5-13 to 5-14

Drive belt

The spindle is belt-driven by a DC motor. Tandon's part number for the belt is 914000-001 (Appendix A, p. A-1). To replace it, turn the drive over with the spindle up, remove the old belt, loop the new one shiny side inward onto the small flanged motor pulley, then turn the spindle while working it onto the large spindle pulley (p. 6-7, Figure 6-1).

Media

The drive needs double-sided, double-density 5.25-inch diskettes, and the IBM floppy adapter adds the requirement that they be soft-sectored. These are the disks sold as "360K", with an unformatted capacity of 500 KB. A double-density disk written or formatted in a high-density 1.2 MB drive does not conform to the double-density standard and may not read in a TM100-2.

Related pages

• Tandon TM100-1
• IBM PC (5150)
• IBM PC XT (5160)
• IBM FDD Adapter
• Floppy Drive Repair
• Capacitor Failure Symptoms
• IBM 5-1/4" Diskette Drive Technical Reference