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Thread: Making a new belt for a Compaq LTE floppy drive

  1. #1
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    Default Making a new belt for a Compaq LTE floppy drive

    I bought this Compaq LTE notebook back in 1991 and used it for some years as a portable terminal, running Kermit to talk to NCR Tower / Unisys 5000 machines when I went onsite at my customers installations. After my dad used it for a few years, it went into the cupboard for many years until I rediscovered it recently and brought it home. I plugged it in and the power supply went click-click-click but after a dozen power cycle events it started up. Unfortunately the hard disk seems faulty now, and attempting to load the LTE diagnostics floppy resulted in nothing happening.

    I disassembled the machine and found the floppy drive belt was now just a broken sliver of gooey rubber that had stuck to the motor and spindle pulleys. Being natural rubber and only 2.3mm wide and 0.28mm thick it was exceedingly fragile, after picking it off with tweezers this was all that was left of it:
    original_rubber_belt_remains.jpg

    I tried seeing if a regular 3.5" floppy drive would work, but the LTE drive was about 3/4 the height of all the regular drives I had in my parts lot and to compound matters it also used a film ribbon connector instead of a plug. So that ruled out a repair with a drive that would fit into the laptop case.

    The drive belt path ran the belt around a fixed idler pulley, to get it clear of some components on the circuit board and to also clear the head impinges upon.
    After cleaning the remains of the melted belt off the pulleys with isopropyl alcohol, I tried a rubber band:
    rubberband_test_1.jpg

    rubberband_test_2.jpg
    With this arrangement the spindle pulley turned, but only slowly. The rubber band was far too thick and rubbed against itself at the idler - a thinner belt was mandatory.

    Thinking back thirty something years, my S-100 machine had a TEAC FD-50A 5-1/4" floppy drive hanging off a VersaFloppy controller. I recalled the FD-50A had a simple untensioned belt that looked like a loop of cassette leader tape stretched between the motor and spindle pulleys, and I always wondered at the time how the belt didn't stretch and fall off. Perhaps something like that would work?

    I measured a cassette tape but unfortunately the width was far too wide and would have rubbed on the board. It was also narrow enough to cause problems trimming to the required width.
    So I decided to cut a strip to the required width of 2.3mm from a VHS video tape. I wanted some metres of it for experimentation in joining the ends with different adhesives.
    VHS_tape_1.jpg
    VHS_tape_2.jpg

  2. #2
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    To do this I removed the VHS tape reel, secured the loose tape end with stickytape and chucked it in my desktop Unimat lathe. The reel was at the very limit of the swing over the bed and I was unable to get the toolpost behind it.
    Since I was not doing any heavy machining for this job I jerry-rigged a knife with an Exacto #11 blade in a pair of vice grips, which were themselves G-clamped to the toolpost:
    cutting_1.jpg

    cutting_2.jpg

    Definately not recommended machine shop practice! ...but it worked, and I ended up with a lot of material to try:
    band_width_1.jpg

    I had guesstimated the circumference of the original rubber belt at 235mm, so I cut the tape to 240mm and after scraping off the oxide, super glued the tape with a 5mm overlap. This band turned out to be a bit big so I made another at 225mm which seemed to fit:
    tape_band.jpg

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    I didn't want to disassemble the drive completely so using tweezers the belt was fitted in through the head gap. To prevent the belt slipping off the spindle pulley, three blobs of blue tack were placed lightly on after fitting the belt.
    Next the belt was drawn through around the idler bearing and toward the motor pulley. A small hook tool bent from a piece of fine music wire was made to slip the belt onto the pulley, with some good tension evident enough to hold the belt on:
    tape_band_fitted.jpg

    Whilst doing this I broke one of the motor wires where it was soldered to the board, but fixed this later. Turning the spindle by hand turned the motor without the belt slipping or coming off, so all good so far.

    After connecting the ribbon cable back I gingerly tried booting the Diagnostics floppy and got this result:
    success.jpg

    Now I have a the other problems to sort out, but at least the floppy drive works again

  4. #4

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    I hadn't imagined tape material would replace the rubber belt. There has been some discussion of this in other searches I've made but never a mention of VCR tape. Good fix. I'm dealing w/ the same problem on a lte 4/33c. I just picked up an immaculate lte 286 but that floppy drive there seems fine, thankfully. Any chance you could send me some of your tape stock. I'd love to try your fix. Good photos!

    I noticed the belt layout is completely different between your drive and the one I'm dealing with. I do know the two drives have different part numbers.

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    No worries, if you would like my 2.3mm wide stock just PM me your address and I'll get some on its way to you - I have plenty left . There's no guarantee how long the belt will last but so far, it's still tensioned and working after nearly a week.

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    Ebay has a few sellers with rubber belts of all kinds. I fixed my 720K Panasonic floppy drive that way as well as my old Technics tape decks.
    What I collect: 68K/Early PPC Mac, DOS/Win 3.1 era machines, Amiga/ST, C64/128
    Nubus/ISA/VLB/MCA/EISA cards of all types
    Boxed apps and games for the above systems
    Analog video capture cards/software and complete systems

  7. #7

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    Quote Originally Posted by 1944GPW View Post
    No worries, if you would like my 2.3mm wide stock just PM me your address and I'll get some on its way to you - I have plenty left . There's no guarantee how long the belt will last but so far, it's still tensioned and working after nearly a week.
    Lol..I just noticed where you live. I appreciate your willingness to send some of your material! Just curious, what type of glue did you use?

  8. #8

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    Steve, got your letter yesterday w/ the belt material. I didn't have any superglue laying around so tried some shoe goo. I'm beginning to admire your finesse as I am struggling to mount the belt and I'm normally pretty handy with just about everything...bulldozers to pocket watches. I'll update this post as i progress. My Dad is a stamp collector so was interested in your envelope. Thanks again.

  9. #9

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    I know this thread is old, but I was hoping to see how well this belt solution was holding up after a year. I have two Compaq LTE/Lite laptops that work great with the exception of the diskette drives, due to broken/stretched belts. Others are selling the drives but they have the same problems so far. If the VHS tape solution is still working out well, I would be interested in getting some of the stock or having some made if any is still around.

  10. #10
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    Sure. There's good news and bad news about this computer, however. First, the bad news. Not long after I got the floppy working and booting a diskette, I still had power supply problems with it. The supply LED would pulse (probably bad caps not charging properly?) so I had to flick it on and off a few times before the LED would stabilise and the computer start up. I had the battery door open and the mostly dead battery pack partially out (ie. not connected) when I was powering up, and I unthinkingly shoved the pack back in... this instantly killed something in the machine and it no longer powers up at all I have not yet opened it up again for meter and scope checks owing to bench space taken over by other projects in the meantime.

    But in answer to your particular question, the good news is I just jammed the drive door flap open and using a wooden stick tested the rotation of the drive spindle inside. It moves well and I can feel the motor pole resistance as I turn it. So the belt is definately still on and tensioned.

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