400k Drive Repair Guide - A Call to Arms!!!!!!

I have a handful of 400k drives in various states of disrepair. Some show signs of life, but don't read floppies, some appear as dead as a door nail. I've searched the internet high and low for a repair guide or how to in the hopes that I'd be able to service or repair these drives. I found one site that offered some tips, but it is out of date and the images are less that stellar.



As far as head alignment, I heard that is some serious business involving an oscilloscope. I'd love to know more about that. If anyone can offer instructions that would be great.

What I'd like to see is this post become the definitive guide for the service and repair of 400K drives. Please contribute how to's, repair guides, tips/tricks and pictures! We love pictures!

These drives are getting harder and harder to find as the years go by and the prices go up and up. We need to combine our collective repair and servicing knowledge in order to keep our 128s and 512s going. 20 years ago, I'm sure repairing these was common. Now it seems to be a lost art.

Thanks.

Larry Pina's book 'The Dead Mac Scrolls' has some useful information on fixing 400k, 800k and 1.44Mb floppy drives and a section on how to re-align the heads without the need of an Oscilloscope. That tends to deal with the later drives rather than the earlier ones, but I suspect the procedure is similar.

Well worth getting a copy if you can find one cheap enough.

ISBN 1566 09016 4

Thanks. I just grabbed a copy off eBay for $4.50. Can't wait to get it!

Kepp those comments coming!

Adjusting the head is in most cases not necessary.

Make sure your drive is complete: check that the pressure pad is still there. Without that, the drive will never work.

Here's how to clean and lubricate the drive.

- Remove the complete top assembly that holds the floppy disc ( release the lever from the eject motor )

- The mechanism will be completely stuck due to old grease that has hardened. Soack the assembly in WD40 for a few hours or if you have the WD40 Spray: spray all the moving parts multiple times, leaving 1/2 hour between treatments, until you can move the mechanism again.

Patience is the issue: do not try to move the mechanism with force, wait until the WD40 has solved all the old grease and dust.

- Once the mechanism is moving smoothly again, then clean all the WD40 from the assembly.

- Lubricate all the moving parts with a small amount of white lithium grease

- Now is a good time to clean the Head: clean it with at least 99% pure Isoprophyl Alcohol.

- Mount the assembly back on the drive and re-connect the lever to the eject motor.

Now try test the drive. First verify that all parts work. Insert a Double Density disc and see if the main motor spins the disc and the head moves.

Also try the eject mechanism.

If everything works, then mount the drive back in it's enclosure ( external is best to test ) and connect the earth wire.

Now try to initialize the floppy disc: If it formats without bad sectors, then the drive is repaired.

If not then inspect the head under a magnifying glass: it it's scratched or damaged then it's beyond repair.

Otherwise you have to adjust the head.

Look at your floppy disk for damage: if the head pushes too much on the floppy disc, then you will see circle scratches on the disc.

Best practice is to set the head as low as possible and keep trying until you can initialize your floppy disc without problems.

For adjusting the head, you needs to remove the PCB at the bottom to get to the screw.

You can find a detailed explanation here:

http://lowendmac.com/tech/after.html

I would not recommend to turn the screw fully clockwise, but do it with little steps of 1/4 turn clockwise until it works.

I know it's a time consuming job, these 400K drives always are....

Good Luck,

Nico

Ah, excellent post! Thank you for the link. That looks helpful.

Sorry for digging up an old post here, but I am having issues with two 400k floppy drives and am curious what your results were.

Were you able to fix any of the drives?

Mine try to read, but fail to read known good 400k disks.

i have (2) 400K floppy drives

as soon as you power the computer on the seek head comes on and makes this click click click sound…

other then that i went all through the drives mechanically tip top shape.

I bet some I/C on the PCB needs to replaced to fix this issue I'm having.

Hello all,

I created a Lubrication guide for these 400k floppy disk drives in October after a noticed a fellow member having some difficulty.

https://drive.google.com/file/d/0B6j6P7lBWw-BNHQ4dXRYZkFGdzQ/edit?usp=sharing

I wonder if one of the keepers of the 68kMLA Wiki would be able to upload this guide to the 'Tutorials and Documentation' section of the wiki as I believe it would be a useful resource for fellow collectors! You have my permission to do so!

i have (2) 400K floppy drivesas soon as you power the computer on the seek head comes on and makes this click click click sound…

other then that i went all through the drives mechanically tip top shape.

I bet some I/C on the PCB needs to replaced to fix this issue I'm having.

Click to expand...

Do these drives have the optical sensor?

i have (2) 400K floppy drivesas soon as you power the computer on the seek head comes on and makes this click click click sound…

other then that i went all through the drives mechanically tip top shape.

I bet some I/C on the PCB needs to replaced to fix this issue I'm having.

Click to expand...

Both drives?

They do have a head sensor in the back. I presume for parking/setting initial location. Same type of "red light" sensors in the front that get blocked by a plastic moving tab.

Dont forget these drives are full of caps too

the mechanics, motors, sensors are all good… been tested with a good PCB… the issue is in the PCB.

i didn't think to check caps… yikes lol… but non of them seem to be leaking

the mechanics, motors, sensors are all good… been tested with a good PCB… the issue is in the PCB.i didn't think to check caps… yikes lol… but non of them seem to be leaking

Click to expand...

You cant tell by that. Only an ESR and cap meter will tell you that

Yup , that is true…

the mechanics, motors, sensors are all good… been tested with a good PCB… the issue is in the PCB.i didn't think to check caps… yikes lol… but non of them seem to be leaking

Click to expand...

You cant tell by that. Only an ESR and cap meter will tell you that

Click to expand...

Thats why i generally just replace the caps without measuring, an ESR would cost me more than the few cents for the caps

Luckily for me, I got 2 ESR meters. One is analog that i bought. And a digital one that was given to me for a present.

I picked up an LCR meter as well, which is handy to have. They do make ESR/Capacitance combo meters but eh...

techknight said:

Dont forget these drives are full of caps too

Click to expand...

I'm rather surprised no one listed what those capacitors are in the 400k drives, nor do I find any discussions or YouTube videos on recapping them.  So I guess that means I need to do it.  Well, here's the first step:

Big PCB:
3pcs of 47uF 16V, D=6.5mm, H=8mm, Lead Spacing=2.5mm
2pcs of 22uF 16, D=5.1mm, H=8mm, Lead Spacing=2.5mm

Small PCB:
2pcs of 10uf 16v, D=4.2mm, H=7mm, Lead Spacing=2mm
3pcs of 10uf 35v, D=5.15mm, H=6.2mm, Lead Spacing=2mm
0.47uF 50V, D=4.2mm, H=6.2mm, Lead Spacing=2mm (or less)
0.22uF 50V, D=4.2mm, H=5.8mm, Lead Spacing=2mm (or less)
1uF 50V, D=4.2mm, H=7.5mm, Lead Spacing=2mm (or less)

I next need to put together a Mouser Cart with the appropriate replacements.  The key here is to not go beyond the Diameter or height, as many of these caps are a tight fit.  The tallest 7.5mm capacitor on the small circuit board is the absolute tallest you'd want to go.  And don't think about using 5pcs of 10uF 35V, forgoing the 2pcs of 10uF 10V, seeing the Diameter spacing on the circuit board necessitates the two different voltage ratings due to the difference in capacitor Diameter.

Also note that you will need thermal grease for the copper heatsink, as that is used between the copper and the silver metal chassis of the drive.

I'll probably do a video on this once I order and then receive all the parts.  But I've been putting together a capacitor list on Mouser for the last two months, checking all my analog boards, motherboards, floppy drives, GCC Hyperdrive (which has its own PSU, and there are caps on the HDD itself too!), and so on.  It make take me another month before it all comes together and I can start on the video.  Suffice it to say, if a lubed floppy drive doesn't work and the cable and heads are good, it could come down to unstable operation due to the capacitors.  Again, I'm really shocked no one has focused on this.  It's not like the motherboard always needs recapping but the floppy drives are somehow immune.  They have electrolytics too, and many were built in 1984, meaning those caps are now 35 years old in 2019.

interesting, I have a hunch the caps might be the reason my 800K drives do not work at all. Do you have caps list for 800K drives as well?

@CharlieFrown

Your hunch is rooted in sound engineering reason.  Why should caps on a motherboard alone go bad after 30 years and not electrolytic caps everywhere else?  ANSWER: They ALL go bad.  So yes, caps alone could create problems for many floppy drives.

I've not opened an 800k drive yet.  My next drive to open is the SE/30's 1.4MB SuperDrive.  For now, here is my 400k floppy drive capacitor list with my Mouser replacement list (none are polymer because I don't have a schematic to know if the super-low ESR would causing timing problems, but all the caps shown below are 5000h @105°C and many have ESR perhaps lower than the stock capacitors, yet probably not too low to cause any problems):

Macintosh 400k SONY Floppy Drive Electrolytic Capacitors

Big PCB:

6pcs of 47uF 16V, D=6.5mm, H=8mm, Lead Spacing=2.5mm (Mouser: UTT1C470MDD1TP)

4pcs of 22uF 16V, D=5.1mm, H=8mm, Lead Spacing=2.5mm (Mouser: UPW1C220MDD6)

Small PCB:

4pcs of 10uf 16v, D=4.2mm, H=7mm, Lead Spacing=2mm (Mouser: UTT1C100MDD1TP)

6pcs of 10uf 35v, D=5.15mm, H=6.2mm, Lead Spacing=2mm (Mouser: UMV1V100MFD1TP)

2pcs of 0.47uF 50V (could be 16V), D=4.2mm, H=6.2mm, Lead Spacing=2mm (Mouser: USV1HR47MFD)

2pcs of 0.22uF 50V (could be 16V), D=4.2mm, H=5.8mm, Lead Spacing=2mm (Mouser: UMV1HR22MFD)

2pcs of 1uF 50V, D=4.2mm, H=7.5mm, Lead Spacing=2mm (Mouser: UTT1H010MDD)

I lack time right now to link up all those Mouser model numbers, and since this forum won't allow me to edit my post many hours from now, just copy the individual part numbers in bold above and and paste them in Mouser's search field to see the capacitor specs.  I spent a lot of time making sure Diameter and Height were appropriate so the replacements would fit.  This is a very important consideration on floppy drives where space is tight!