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Tandon TM-848E (Single Sided??)

maxtherabbit

maxtherabbit

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I picked up this drive on ebay for about $70 shipped. The seller listed it as "in original packaging" but the photos were very limited. The price was so good that I took the chance on it actually being NOS. It wasn't, however it is in good condition. The termination resistor pack is gone, the jumpers are messed with, there's insertion wear on the edge connector, and the troubling thing - the alignment screws appear to have been tampered with.

For the price I don't think I got screwed necessarily if it works, but I haven't tested it yet. Tomorrow I'll get into the shop and find out. What really bugs me about this thing is that despite clearly having both index sensors, it only has one R/W head!! Apparently Tandon made this model in both single and double-sided variants (which I knew) but even the single sided drive has both sensors :tellme: The double sided one is just not connected.

I thought I was getting a NOS double sided 8" drive and ended up with a used single sided :( Seller stipulated no returns and did not list it as "used" or "new" so I have no recourse with ebay. Do y'all think I got hosed? Should I worry about the alignment screws' match marks being jacked up?

The 'E' variant is rare enough to not be commonly discussed or encountered, so having a working one of those would be worth something in it's own right. Its direct drive DC spindle motor and built-in write current switch are super nice as modern features on an 8" drive. Worst case I could probably sell it on here for parts if the alignment is smoked, or perhaps a kind soul would let me borrow an 8" alignment disk.
 
Well, the SS -1E is definitely rare so you can be excused for assuming that it was the double-sided -2E version; perhaps the seller didn't realize that it came in SS and DS versions, but if he did I think he should definitely have specified that it's SS.

Why not ask the seller if he knew; if not, maybe you can work something out.

BTW, the other main improvement aside from the direct drive motor is that the -E uses a microprocessor instead of discrete logic.

Good luck!
 
MikeS said:
Well, the SS -1E is definitely rare so you can be excused for assuming that it was the double-sided -2E version; perhaps the seller didn't realize that it came in SS and DS versions, but if he did I think he should definitely have specified that it's SS.

Why not ask the seller if he knew; if not, maybe you can work something out.

BTW, the other main improvement aside from the direct drive motor is that the -E uses a microprocessor instead of discrete logic.

Good luck!
Click to expand...

The seller did not specify whether it was single or double sided, that was on me. I saw both index sensors and...
 
In the first picture is there only one cable attached to the black connector in the lower left hand corner of the PCB?

That connector should be where the R/W heads connect to the PCB. That area of the photo posted here isn't too clear.
 
gslick said:
In the first picture is there only one cable attached to the black connector in the lower left hand corner of the PCB?

That connector should be where the R/W heads connect to the PCB. That area of the photo posted here isn't too clear.
Click to expand...

There is only one R/W head, of that there is no doubt. Tried to capture a picture of the felt pad on the upper arm assy in the third picture, but it didn't come out great.
 
maxtherabbit said:
The seller did not specify whether it was single or double sided, that was on me. I saw both index sensors and...
Click to expand...

I know, I looked up the listing; I just thought that if the seller honestly thought it was double sided (which presumably makes it worth more) he might be amenable to a little adjustment.

It is odd that it has both index sensors, that doesn't sound like Jugi Tandon ;-) Is the model number specifically TM848-1E ?
 
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MikeS said:
I know, I looked up the listing; I just thought that if the seller honestly thought it was double sided (which presumably makes it worth more) he might be amenable to a little adjustment.

It is odd that it has both index sensors, that doesn't sound like Jugi Tandon ;-) Is the model number specifically TM848-1E ?
Click to expand...

Model according to the nameplate is TM848E. No dash, no '1'.
 
That doesn't surprise me. After all, the only difference is a top-side head. I'm certain that the PCB's identical to the double-sided version.

Tandon was a bit sloppy on part labeling. I've got some TM-100-4Ms that have a sticker that says "96 tpi" on the door latch, where the drives clearly are 100 tpi models. My guess is that since the bezel and latch mechs are the same, someone ran out of the 100 tpi labeled ones and just grabbed a few of the 96 tpi ones.
 
Did some basic tests on the drive today. Turns out I had the exact same problem as was documented here: http://www.vcfed.org/forum/showthread.php?53777-TM-848-8-quot-Floppy-Drive-Error-Codes

Right down to it actually being the write protect sensor that is defective, not the track 0 sensor. I bypassed the write protect sensor temporarily by shorting pins 3-4 to close the circuit for the T0 sensor's LED. I would like to replace it, however the HOA1887 that Chuck suggested in that thread is now out of production and I cannot find one. Any suggestions?

Other than that, the drive seeks properly and the spindle motor and electronics all check out. Still need to fab up an interface cable to actually R/W from a PC but I have a good feeling that it's fine.

The blink codes in the manual are just wrong BTW. Based on my drive as well as pski's.

Manual says 3 flashes, then 2 is "fails to step in from track 0 or track 0 sensor is always equal to zero" this is incorrect. The correct blink code for this condition is 3 flashes, then 1.

Manual says 3 flashes, then 3 is "fails to step out to track 0 or track 0 sensor is always equal to one" this is incorrect. The correct blink code for this condition is 3 flashes, then 2.

Manual says 3 flashes, then 4 is "no index pulse with lever closed" this is incorrect. The correct blink code for this condition is 3 flashes, then 3.
 
drive seems to be aligned! I don't have a real alignment disk to test with, but using the half-assed alignment test in IMD it is reading all the sector marks with no errors on some SSSD disks I had lying around
 
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I have to say I am a fan of this drive. It seems well built and works great so far. It is a far cry in quality from my only other Tandon experience (TM-100).

Are the belt driven TM848s similarly good, or did they just put their best effort into this one?
 
I never cared for them. Watch out for the electrolytics on the +24 side. I've had a couple where one failed short and took out the 7812 regulator and associated resistor. The drive electronics always seemed to be a bit strange to me with the schizophrenic +12/+24 divide.
 
Chuck(G) said:
I never cared for them. Watch out for the electrolytics on the +24 side. I've had a couple where one failed short and took out the 7812 regulator and associated resistor. The drive electronics always seemed to be a bit strange to me with the schizophrenic +12/+24 divide.
Click to expand...

I'd be somewhat more forgiving of such a simple electronic failure that I could repair easily. Granted no failure is really "acceptable" but I was really thinking more about major mechanical assembly failures and alignment retention.
 
Well I was wrong about the second index sensor not being connected, it is connected and works. The drive will happily read and write to side 0 of a two sided disk with only the DS witness hole punched in the jacket.
 
I've been using the DP8473V to control the drive. I found this tidbit in the datasheet:
Note for FM encoding: Sometimes, after a reset, the DP8473 will consistently
return an error in the Result Phase after an FM read command. If this
occurs, simply reset the DP8473 and retry the operation. This may have to
be done more than once, as many as five times. Resetting and repeating will
prevent soft errors being reported prematurely. This technique is used by
MS-DOS.
Click to expand...

I seem to be encountering this problem. It manifests itself in IMD with occasional "no address mark" errors at the first track of a read operation. Once this occurs no tracks can be read. When IMD does not encounter the error on track 0, no subsequent errors are ever encountered. In 22disk (my first time trying it, nice program btw Chuck) I will occasionally get sector not found errors on transferring a CP/M file to DOS. In both programs, no write errors have ever been encountered, and upon a quit and retry the reads work normally.
 
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