Any experts on copper here? - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 23, 2024, 01:11:02 am
content: I mean the metal and how it behaves when drawn out into fine wires. You know, like in a floppy drive read/write head coil. This is another one of my vintage computing threads.A lot of Mitsumi brand 5.25" drive heads fail for a mysterious reason. The symptom is, of course, that the drive can't read a floppy anymore. The measurements show the coil(s) (there are three) resistance go up from about 15R normally to 30+ ohms.Of course no one measures the heads continuously so I don't know if it changes smoothly or all at once, since we only measure once it's dead.So the question that keeps me up at night, is what is the cause? Some people say "oxidation" but I don't know what that means. Zillions of headphones and earbuds and tape recorders (and hard drives!) have been made over the decades and if oxidation was some danger for copper, it would have cropped up in all those other places that also use fine wire, no?Also the drive heads are potted in a mysterious goop so oxygen from the air is unlikely. If one wants to stick to oxidation as the cause, maybe the oxygen is the one that's already in the wire.Of course materials are complex, and it's not just a series of little copper atoms lined up like beads in a wire. There are all kinds of weird and wonderful things that material science teaches us, none of which I master.Soooo..... long story short, does anyone know if drawing out 40AWG wire and make a square cross section coil around ferrite can cause some kind of dislocations of the copper ... crystal, matrix, whatever, that can propagate over time and slowly cause resistance to go up?There's even a copper information website out there.https://www.copper.org/publications/newsletters/innovations/1997/12/wiremetallurgy.htmlLots to read.In other words, can these heads be rescued? Like, I don't know, cryogenic soaking for a week.

author: coppercone2
author_rank: Super Contributor
timestamp: October 23, 2024, 01:13:49 am
content: unwrap it and measure a meter

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 23, 2024, 01:15:59 am
content: I wish, it's tiny in there and so far all my disassembly efforts are destructive...

author: Analog Kid
author_rank: Super Contributor
timestamp: October 23, 2024, 01:20:52 am
content: Sorry, no expert on copper metallurgy here. What you report about increasing resistance is surprising and puzzling.This reminds me of a job I had long ago, actually my first "real" job in the computah industry: I worked for a small company that sold media conversion systems for PCs, mainly floppy-drive systems and software that allowed you to read, say, a System 36 or DEC diskette on your PC.At the time (late 1980s) we were still selling a ton of 8-inch floppy systems, using Mitsubishi drives. One of my tasks was to improve the error reporting of one of our conversion utilities, and of course in order to do this we had to generate ... errors.Well, that turned out to be difficult if not damn near impossible. I remember taking an 8" floppy and running over it on the carpet with my office chair casters, repeatedly. Tried reading it: zero errors. Ran over it some more; still no errors. Those things were built like friggin' tanks. I think we actually ended up punching holes in it or something drastic like that.Of course, 5-1/4" (and later 3-1/2") floppies were more error-prone due to their higher density, but even those were pretty damn robust.

author: coppercone2
author_rank: Super Contributor
timestamp: October 23, 2024, 01:20:59 am
content: well, if you figure out how to get a sample, you can measure resistance to see if there is a elongation or corrosion or tempering (tempering increases resistance)it would answer the question, I think your focus should be to figure out how to dismantle it

author: uer166
author_rank: Super Contributor
timestamp: October 23, 2024, 02:36:13 am
content: Are you 1000% sure it's a single coil, and not perhaps a bundle of parallel conductors like Litz? The only reason I mention that is that the numbers such as 15 and 30Ohms sound suspiciously like multiples.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 23, 2024, 02:48:11 am
content: Quote from: uer166 on October 23, 2024, 02:36:13 amThere are three coils, two for read/write and one "erase" coil which is really the trim band coil that trims the edges on each side of the gap.Sadly I've not taken great notes along the way, I can't tell you which coil went bad on this head in the photo.

author: bostonman
author_rank: Super Contributor
timestamp: October 23, 2024, 03:00:39 am
content: Have you looked on Lemon64? Someone has had some success rewiring them.I know this is deviating from you question, but maybe you'd looking to revive some of these drives.

author: edpalmer42
author_rank: Super Contributor
timestamp: October 23, 2024, 03:49:53 am
content: Quote from: Alex Eisenhut on October 23, 2024, 02:48:11 amIf the failure mode is that you can't read a floppy, doesn't it mean that the read head has failed?The other heads won't be involved in the read process. This assumes that the same floppy can be read on another drive.I think @uer166 made a very good point. If the read head consists of 2 coils in parallel - each 30R, if one goes open the measured resistance will go from 15R to 30R. Note in the photo that some of those wires look like two wires twisted together.I've also seen examples where hair-thin copper wires will actually dissolve into the solder causing the wire to break right at the point where it enters the solder blob. Touch the wire and it comes away from the point that it's supposed to be soldered to.

author: DaJMasta
author_rank: Super Contributor
timestamp: October 23, 2024, 07:38:54 am
content: Could it be as simple of them leaving a fairly aggressive flux on the solder connections that is slowly thinning the wire?do you have any small enough clips for you to be able to measure the coil not including the landing pads specifically? If it's just the interface that is going high resistance, the chance of being fixable goes up quite a bit.

author: dietert1
author_rank: Super Contributor
timestamp: October 23, 2024, 08:21:59 am
content: After looking at the image i'd suspect the coil itself might still be good and the issue may be in the wires or flat cables used for external connection. Everything is subject to lots of hasty movements..Regards, Dieter

author: bostonman
author_rank: Super Contributor
timestamp: October 23, 2024, 02:54:33 pm
content: Unless I'm wrong, these are the schematics for the read/write heads just to clarify the confusion on how they are wired.I have little experience with this issue, but I've read several messages regarding the coils opening causing the head to not read disks anymore.Unfortunately many of these drives are junk because trying to wire a new coil is extremely difficult. The OP is basically asking what is making the copper wire fail over time, however, I wanted to point out that if he/she wants to repair it, someone on Lemon64 has been successful wring a new head.