View Full Version : Mitsubishi M4853 floppy drive head load sticks

December 24th, 2016, 05:28 AM
In the quest to add a mini floppy drive to my CompuPro 816, I took a chance and purchased a Mitsubishi M4853 drive advertised as NOS but untested, as is.
The drive does look brand new and works great BUT (with old equipment, there's usually a BUT) after the head carriage is raised to put in a disk, the head load sticks in the up position.
I disassembled and found the head load relay has a metal lever that when raised rests on what appears to be a rubber bumper that turned to goo. I could see the goo hanging in there.
It is inside the relay and I can reach in with a narrow strip of alcohol wipe and it keeps coming out black. The thing has just turned to adhesive which I can't seem to clean up.
I had a similar problem on my NEC 1165 8" drive but it was all exposed so I just removed it. It clatters a little more but has worked great. This one is buried inside the relay.
Is there something I can treat it with to make it not stick? I was thinking graphite or Teflon type stuff. It would have to be a tiny drop that I insert with a really small screwdriver blade.
I thought about WD40 or a light oil but that would probably keep attacking the rubber, or whatever material it is. I know this forum has floppy drive guru's. Ideas ???

December 24th, 2016, 08:51 AM
Sounds like the same issue with some tape drive capstans, they turn to goo after a period of time. The only fix will be to disassemble the relay and clean out all of the goo, then rebuild the bumper. People rebuilding tape capstans have used various material, including silicone or vinyl tubing, vinyl heat shrink, or silicone "rescue" tape (i.e. self adhesive when stretched), as well as more modern capstan materials. The idea for capstans is to build it up to somewhat more than the required diameter then spin the motor and remove some material to get close to the required diameter. For your bumper, it will probably be easier since you won't need to get it circular.

December 24th, 2016, 10:04 AM
No, there's nothing that will make the goo non-sticky. You'll have to remove it or at least remove as much of it as you can.

I find that soap and water tends to make the goo stick a bit less, rather than a solvent, but it's still a very messy job.

On the other hand, if your Compupro system manages the motor control (i.e. the drive motor isn't running continuously), you can probably get by with chucking the solenoid entirely. On most later drives, the head-load mechanism was an option and usually not present. Looking at my 4853, I can see that removing the solenoid and the lifter bar will get the job done for you.

December 24th, 2016, 10:45 AM
I've had lots of experience dealing with this problem on the Mitsubishi M4853. The rubber bumper pad is not necessary for the drive to function properly, it appears that it is only there to deaden the sound of the Head Load Mechanism working. Neither is disassemble (other than removing the logic board) to remove the remains of the bumper pad. Keep working fresh alcohol pads into the gap in the two sides of the head load solenoid and continue to work clean surfaces of alcohol pads between the two sides of the head load mechanism until the pad stays clean, signaling that is the rubber pad has been completely removed.

If you don't bend anything while cleaning out/off the rubber bumper, no readjustments should be necessary, although the logic board needs to be replaced exactly as it was, because the index pulse sender is mounted to the logic board, and moving the logic board moves the index pulse timing.

Removing the Head Load Mechanism is a bad idea, since there will not be sufficient clearance for a disk to be inserted and retracted from the drive without possibly hanging up on the upper head assembly (the Head Load Mechanism increases the creates the clearance for a disk to be inserted or removed when the heads are not loaded), which can result in permanent damage to the upper head assembly.

FYI: Mitsubishi 2896-63 1/2 height 8" DSDD floppy drives suffer from the same problem with the deterioration of the rubber pad on the Head Load Mechanism, and the solution is the same.

December 24th, 2016, 05:59 PM
Thanks for the advice, guys. I removed the solenoid and kept feeding in alcohol head cleaning pads cut into strips until I was hearing metal to metal working the lever.
I was able to get a small screwdriver inside to release chunks. I put it back in and it works fine. That goo was like tar.3498134982

December 24th, 2016, 07:07 PM
Yeah, something not mentioned a lot, but the "rubber disease". It seems to only peripherally be related to age--I've run into late 90s Travan tape drives with turned-to-goo pressure rollers, but found 70s tape drives just fine.

The other side of this is rubber that dries out and goes crumbly. I've researched this and there doesn't seem to be a solution other than cleaning and replacing. Sometimes, you can find a substitute that works almost as well, such as Tygon tubing and there are rebuilders for items such as pinch rollers, but it's a lousy situation.

December 24th, 2016, 07:26 PM
Is there any photos of what a CompuPro mini drive enclosure looked like? My Google foo isn't turning up anything.

December 24th, 2016, 10:00 PM
Is there any photos of what a CompuPro mini drive enclosure looked like? My Google foo isn't turning up anything.

There isn't a specific Disk Enclosure for 5.25" drives. Compupro made two Drive Enclosures that would house two 8" rackmount drives horizontally, side by side. The 1st/Original Version was made to house two full size 8" floppy drives (never meant to house an 8" hard drive). You can spot the early disk drive enclosures by the fact that it about two inches deeper than the 2nd design, and has five screws holding the chassis to the cover on each of the two sides (the shorter chassis 2nd design has four screws holding the chassis to the cover on both sides). The early long chassis had a single punchout for a 50-conductor connector. Later long chassis had additional punchouts for a 20-conductor and a 34-conductor for a 5.25" hard drive or mini-floppy drive. The on/off switch was mounted on the rear and was the same size as the Compupro Mainframe on/off switch.

There was also a 3rd, short-lived intermediate length chassis design, shorter that the early long chassis, and longer than the later short chassis which was offered for a short time between when the 8" full height floppy drives were offered, and the introduction of 5.25" half height drives (mini-floppy and tape). These not not seen very often. The rare intermediate length chassis is most often seen with 8" half-height floppy drives, and carries the full size on/off rocker switch of the S-100 Mainframe.

Short chassis came with the same full size switch when introduced but switched to a smaller rocker switch (like the switching power supply Mainframes used), and came with one punchout for a 50-conductor 8" floppy connector, and two sets of punchouts for 5.25" hard drives or mini-floppy drives.

Compupro designed and built different adapter plates/mounting brackets to fit different size drives in different configurations adapting the 8" drive bays to 5.25" full height and half height drives, as well a half height 8" floppy drives. There were brackets to mount two 8" half height drives stacked vertically, single 8" half height drives with a cover over the top half of the bay, 8" half height drive with a 5.25" half height drive mounted above, 5.25" full covers that a hard drive could be hidden behind, and brackets with an opening to fit a full height, or two half height 5.25" drives , and another mounting bracket with an opening to fit a single half height 5.25" drive. At one time I had dozens of extra mounting brackets in stock (order them from another Compupro Authorized Dealer who had high quality duplicates of the Compupro brackets made). My supply of mounting brackets is about exhausted now, and I've played with the idea of looking for a company to duplicate the various brackets. But I'm concerned that I won't be able to get my money back due to the small market.

There were also three power supplies with a standardized mounting base that could be fitted to either chassis size. The original power supply was designed for/to run 8" floppy drives and had outputs for 24V+ and 5V+. The 2nd design has five outputs and is designed to run up to three drives of two types (8" floppy, 5.25" mini-floppy, 5.25" tape drive, or 5.25" hard drive. The 3rd design has up to six voltage outputs and will handle up to four drives of three different types at the same time.

The 2nd and 3rd power supply designs were configured at Compupro for each individual order from an Authorized Dealer. There were different transformers mounted,depending on what outputs were specified. Individual outputs used the same power/bypass transistors, but control components were changed to get the specific voltage outputs required.

At one time I had five to ten spare power supplies tested and ready to sell or exchange, and another five to ten power supplies I was using for parts. The number of spares has been used up or sold over the years, and now I'm down to the last half dozen power supplies and parts donors. Transformers are scrapping bottom for spares. I can still repair power supplies, and in general they are extremely reliable. People usually buy power supplies when they are upgrading their Drive Enclosures from 8" floppy only to a different configuration that includes some sort of 5.25" drive/s.

Right now I have one used long chassis and one new short chassis left for sale. Prices will vary depending on options chosen (advanced power supply and/or drive mounting brackets). The older long chassis starts at $300 with the original 8" only power supply and no additional drive mounting brackets (none required to mount 8" full height drives). The short chassis will start at around $500 with the dual 8" power supply,and extra charge for an advanced power supply or drive mounting brackets. Compupro offered two different colors for cabinets over the years and I think I have used covers in both colors available. I suppose that I could could find a source for chassis/bases I could build a few more complete Disk Enclosures with mostly Compupro parts. Full height drivesdo not fit in the short chassis.

I have two Drive Enclosures connected to my personal system, and if you want to see what the late enclosures (in the late color) look like with an assortment of 8" and 5.25" drives installed, send me your email address, and I'll send you a couple of photos.