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Is it possible to repair a FDD head?

I

iz8dwf

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Hi all,
I'm posting here instead of the Commodore forum since this is probably a very general HW question.
I was repairing a few CBM 1541 FDDs and I've found one with a bad R/W head. It measures about 1.5kohms instead of the usual 32-33 ohms. The "erase" part is fine, at least on a ohmeter. I assume the erase is a separate coil inside the head.
This particular mechanic is a Mitsumi/Newtronics D500.
Is it possible to service/repair the bad head or the only option is finding a new mechanic or the whole head assembly?

Thanks
Frank IZ8DWF
 
I've never heard of a head burning out, although if exposed to enough current that is possible.

How exactly did you measure the resistance? Directly at the head or through the small cable that connects it? I have seen several drives where the cable was not really as flexible as it should have been, and the wire inside simply broke after heavy use.

A cable can sometimes be repaired, but other than that, I am not aware of anyone ever "fixing" heads.
 
SomeGuy said:
I've never heard of a head burning out, although if exposed to enough current that is possible.

How exactly did you measure the resistance? Directly at the head or through the small cable that connects it? I have seen several drives where the cable was not really as flexible as it should have been, and the wire inside simply broke after heavy use.

A cable can sometimes be repaired, but other than that, I am not aware of anyone ever "fixing" heads.
Click to expand...

I tried to move the cable all along its length, but the reading was very stable. I assume that an interrupt cable would show infinite resistance, rather than a stable 1k5.

Frank

PS: yes, it's the first time also for me to find a broken head.
 
It can happen (the windings are very fine), I suppose. All you'd need would be a shorted driver, or perhaps a power supply error and *poof*. I've never heard of someone repairing a floppy (or hard disk) head--I doubt that it can be done.
 
Chuck(G) said:
It can happen (the windings are very fine), I suppose. All you'd need would be a shorted driver, or perhaps a power supply error and *poof*. I've never heard of someone repairing a floppy (or hard disk) head--I doubt that it can be done.
Click to expand...

This same drive had a wrong chip inserted into a socket (LS00 instead of 06), so it might be an absent-minded (or worse) person at one time plugged the head connector into the stepper one (it can be done on these drives, unfortunately, and the two connectors are side by side), so in that case I think the magic smoke would leave the head instantly.
I asked because someone on the cmb-hackers mailing list said there was one person repairing these heads (not just substituting them). So I wondered if there was some well-known procedure.
I think it's better to start the hunt for a new D500 mechanic.
Thanks
Frank
 
Boy, I don't know how that (head repair) could be done. The thing is probably potted in epoxy. Perhaps "head repair" in this sense really means "head supports"?
 
Chuck(G) said:
Boy, I don't know how that (head repair) could be done. The thing is probably potted in epoxy. Perhaps "head repair" in this sense really means "head supports"?
Click to expand...

Yes, I thought exactly the same. He said it was really the coil substitution. So probably he knows a way to remove the epoxy (boiling the head?) and put in a new coil. It must be quite a long and delicate procedure.
I guess it would be worth doing it on a rare 8" unit, maybe.
 
Often devices with small coils and fine wire fail after time. Its usually due to the residual flux not being cleaned off the connection points internally at the time of manufacture. They can suddenly assume a higher resistance rather than going totally O/C. Exactly the same thing happens with L-C delay line modules on memory boards and other logic circuits and also magnetic phono cartridges do it too, as do the coils on meter movements. With these things with enough patience and magnification they can be repaired/rewound successfully only sometimes and resin potting is also a barrier to success.
 
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