How to modify the Spindle Speed of a 3 1/2 Floppy Drive? - Page 1
Forum section: electronics / general

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: April 17, 2025, 08:39:11 am
content: I am looking for way to mechanically replace a SONY OA-D32W floppy drive with a more "modern" one. besides the different pin-out of the drive's interface (compared to the newer ones) which is easy to overcome, the main hurdle of replacement is the OA-D32W's spindle speed of 600 RPM. i have an EPSON SMD-1300 and a SONY MPF920-E for testing. Is there any way to modify the spindle speed of those drives from 300 RPM to 600 RPM?(yes, i have successfully tested a GOTEK floppy emulator, but i'd rather have a mechanical replacement to preserve the looks of the drive unit.)

author: amyk
author_rank: Super Contributor
timestamp: April 18, 2025, 08:10:56 am
content: It depends on the motor servo IC and how it's configured. If you post some pictures or at least find the part numbers used on them, that might yield more information.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 18, 2025, 08:57:37 am
content: Quote from: Le_Bassiste on April 17, 2025, 08:39:11 amEverything is tuned for that specific RPM.- the reading/writing interface and pulses width- the writing currents- the amplification level for the reading heads- the PLL loop dealing with normal RPM fluctuations- even the endurance of the magnetic material of the disk and the heads are made for a given RPM, not faster- most of all, the data encoding/decoding is not made inside the floppy unit, it's prepared in the computer (in the floppy disk controller), so no computer will be able to work with a double RPM without modifying the computer too.In short, it won't work any more, and it won't work because of many reasons, not just one.Why do you want to double the RPM?

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: April 18, 2025, 09:27:51 am
content: [ Specified attachment is not available ]Quote from: amyk on April 18, 2025, 08:10:56 amhere you go, couldn't find the exact datasheet of the motor-driver, though:

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: April 18, 2025, 09:39:26 am
content: Quote from: RoGeorge on April 18, 2025, 08:57:37 amnot getting what you want to say with your post, did you even read my question?

author: RoGeorge
author_rank: Super Contributor
timestamp: April 18, 2025, 11:34:33 am
content: The initial model you want to replace is a vintage floppy, and non-compliant with the IBM standard (maybe you should have been specified that), and that's why my misunderstanding. Naming the vintage computer of the original floppy might have helped, too. Nevermind, my bad.About doubling the RPM, from what I know, no 1.44 PC FDD has had a switchable 300/600 RPM mode, so most of the concerns enumerated before (regarding a double RPM) might still stand true (except the last dash point), but since I don't know the vintage model you are trying to replace, won't speculate.Many 1.44 PC FDD used to have just a current driver for the spindle motor, and the clock was external of the motor driver IC. Many were using a 1MHz clock input, for example BA6486, FAN8422, etc. Maybe try to find with an oscilloscope the clock input pin of the BA6986, and double that frequency (by inserting a frequency doubler made out of XOR gates). Not sure if the motor will have enough power to work at double the RPM (or even to start), but it's relatively easy to try.Another try easy to test would be to replace the quartz/resonator of the entire floppy (often a 4MHz one with 3 pins) with one of double of that, so a 8MHz, and hope the entire FDD will still work, but I never tried any of these 2 suggested modifications.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 18, 2025, 01:28:06 pm
content: There are 2X USB floppy drives. Maybe buy a 2X and see what you can do with it? Although these are all slimline drives and your drive is not.For example, Sony MPF88E-UA. I have one but don't know what is the mech inside. I hesitate to take it apart because of brittle plastic.Also I don't know if it can write DD reliably.

author: m k
author_rank: Super Contributor
timestamp: April 18, 2025, 01:56:22 pm
content: Standard floppy drive had 300 and 360 RPMs.That creates a distance that R/W head can pass during a bit.Since the whole operation is analog all parameters are adjusted and are dependent of that.It includes things like write current and magnetic material of the media.So by doubling the RPM you are also altering many other functions and their properties.GOTEK is an emulator, it can bypass all of those analog parts of the operation.If emulator has a setting for 600 RPM it doesn't mean that true analog can do the same.Manual page 2/98 has specifications.Data density is standard, so no problems there, but because of RPM bits are shorter and so higher write energy is possibly needed.I didn't check much more, but it's very detailed manual, so I'm sure you can use its adjustments as examples for other drives.If the drive operates in multispeed mode the standard model can't handle it.Manual has that there is 600/300 switch somewhere, so seems to be a singlespeed thing.Is it for SMC-70?

author: BrianHG
author_rank: Super Contributor
timestamp: April 23, 2025, 02:53:03 am
content: Amiga certified HD 3.5 inch drives were dual speed. Instead of improving the chipset, Commodore had the floppy drive modified to spin at a slower speed when an HD disk was inserted by detecting the stamp out hole in the HD discs.I do not know if this was possible on PC drives, but, there are some PC drive which can be modified into dual speed with a few jumper settings on the drive itself.You just need to Google/Youtube search for making a PC HD drive into an Amiga HD drive and you will see the mods to make the spindle operate at 2 different RPMs + the standard floppy disc detect signal for the Amiga's auto disc swap detector.

author: mikerj
author_rank: Super Contributor
timestamp: June 01, 2025, 09:58:55 pm
content: Quote from: BrianHG on April 23, 2025, 02:53:03 amThe Amiga HD drives ran at half speed (150 RPM) and IIRC the mod required on PC floppy was to add a flip flop to half the frequency of a clock source on the PCB.