Head surgery - Page 1
Forum section: electronics / general

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 30, 2019, 02:54:50 pm
content: The floppy drive head kind. Got a Commodore 1541-II drive here with the D500 Mitsumi mechanism. Looks like a coil can fail open circuit in the head.The blue wire connection is open circuit to the rest of the wires. Yes I checked to see if the wire itself is good from the PCB to the head, that connection is good.I plan on putting in paint stripper drop by drop on the potting compound, maybe it will reveal more detail as I go along.Anybody ever attempt something like this? The thing's a doorstop anyways.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 30, 2019, 03:25:08 pm
content: If anyone wonders here's the schematichttp://www.zimmers.net/anonftp/pub/cbm/schematics/drives/new/1541/1541-II.340503.gifU12 is a LA8200M amplifier,https://cdn.datasheetspdf.com/pdf-down/L/A/8/LA8200M_SanyoSemiconductorCorporation.pdfand CN3 goes to the head assembly. From what I gather the read head is a center tapped winding and the write coil is another winding entirely. Looks like the read head lost a winding connection.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 03, 2019, 02:18:08 am
content: Meh, looks like I'm not the only one to have discovered the coil opening "feaure" of these drive heads.https://retrohax.net/commodore-1541-floppy-drive-fixing-chaos/Still no answer. I wonder if I can rip out the guts of a PC 360K floppy and somehow jam it in the 1541 drive. I know the 1571, the double-sided version of the 1541 can read PC floppies but that's down to the MFM controller but it shows the heads are the same for that kind of media.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 24, 2019, 12:14:57 am
content: FYI, I shoved a LED under the head and took a picture through a microscope.A 48TPI drive would lay down tracks at 1000/48= 20.8 mil pitch (0.529mm). There is a guard band on each side of the track. The data is 12 mils wide with 8.3 mils of dead space.Yup the black stripe on the head measures 12 mils. You can just see the gap in the ferrite. The two wide gaps on the side are the straddle erase heads which create the guard band on each side.Everything points to these things being pretty complicated to build.

author: Rasz
author_rank: Super Contributor
timestamp: December 27, 2019, 03:37:22 am
content: here someone mentions retired Polish (Unitra) engineer repairing heads by handhttp://cbm-hackers.2304266.n4.nabble.com/1541-bad-R-W-head-td4665226.htmldonor PC drive will cost almost as much as c64 one

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 27, 2019, 09:28:44 pm
content: I wonder how I can get the core out of the head since it seems bonded in place with glass.Maybe I can just yank the back of the ferrite off and somehow slip a new winding on there.Microsurgery.Not sure I can just slap a new head assembly into the 1541 mechanism; I've never seen the same head sled thing in two different drives.Plus this mechanism uses straddle erase heads, you can't put a head in there with tunnel erase, the circuitry won't support it.