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Making a new belt for a Compaq LTE floppy drive

1944GPW

Veteran Member
Joined
Apr 26, 2011
Messages
801
Location
Brisbane, Australia
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
 
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
 
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 :)
 
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.
 
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.
 
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.
 
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?
 
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.
 
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.
 
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.
 
I'm sorry about the laptop. I hope that its something simple.

To answer my other questions, is there a possibility of having you build some new stock? I don't have the tools for it and making them by hand is proving to be difficult.
 
I can't find the cassette spool seen in the above photos, but realised I'd saved some of the cut tape and stashed it in the LTE ring binder front pocket. There's a good few metres of it so shouldn't be any problem. I can make up a few belts at 225mm and send them along with a length so you can make your own if they don't fit. Send me a pm and give me some time to make them up. You will need to make the wire hook and find some blue-tack, I could not have got the belt on without those.

Steve.
 
I'm not able to PM you for some reason. The more you can send the merrier as I now have 7 drives with stretched/broken belts or a blob of rubber.
 
80486sx, I'd say you can't PM me until your post count goes up. Anyway, as requested I've made some belts for you.

Here's some more details on how I make them, in case anyone wants to have a try as there are other drives out there that could benefit from small belts such as these. It's not too difficult but patience and good light helps, also a new(ish) tube of superglue.
The most difficult thing is to produce the correct width belt material in the first place, but I think for short length ones as these, a pair of scissors would be adequate to cut them to width along the 200+mm length. Sure, one side might be a little wavy or tapered but that probably wouldn't matter.

Step 1. Cutting the tape to length. Making sure the starting end is clipped neatly, lay out the tape material along a ruler and cut to the required belt circumference plus 5mm for the overlap. You can use sharp scissors for this, as its really not critical, just clip a little at a time. Tools I use here are the sharp scissors, #11 and also curved Exactos, and a jeweller's 3x loupe to inspect the results:
attachment.php


Step 2. Scrape the oxide off. First, determining the oxide side is usually easy - look at the tape surface on bothe sides, they will both be shiny but the oxide will be shinier. Using a curved Exacto blade, GENTLY scrape the tape from 5 or 8mm back from the edge to the end. Thirty or so very light scrapes will do it. The curved blade is important as a flat #11 blade does not scrape properly.
If you scrape too hard the tape stretches or tears so once again LIGHTLY is the go. Also do a very short scrape on the underside of the other end (which has no oxide) so that the surfaces to be bonded are both keyed as much as possible.
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Finished result:
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Some belts cut to length, scraped and ready for joining. A few of these later failed when tension-tested:
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Step 3. Preparation for bonding. On a flat metal surface that you can wrap the belt under, use a strip of fridge magnet (flexible, not very strong stuff used for advertising) to hold the oxide-surface-up end down. I used the handle of a small engineers square as it was short enough to have the belt easily reach around each end. A strip of paper keeps the belt from adhering to the steel, or you can also put a layer of stickytape on the steel surface beforehand to do the same.
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Step 4. Bring the other end of the tape (oxide to the top, polyester base down) around under the steel surface and put on the table to hold it flat as you don't want to make a Mobius strip here.
 

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(continued)
Step 5. Using another strip of the flexible fridge magnet, clamp down the other end. You can then slide it around to get the overlap to 5mm and also set it straight.
Step 6. Once aligned, carefully lift the top end with tweezers or the knife blade to drop a tiny bit of superglue on the scraped surface, then drop:
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The excess glue can be soaked up with a cotton bud which can also be used to apply pressure whilst setting. Pressure must be put on the join or it will not bond properly:
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Step 7. Once dry, the belt can be lifted off the metal clamping surface and checked. Leave them for a while then aply some light tension to check if the bond was successful. If not - make another one. If there is a slight misalignment then sharp scissors can be used to cut the skewed bits off the join:
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And for completeness sake, here is an alternative to gluing: I've found that the polyester videotape material takes well to welding.
Step 1. Set the soldering iron set to under half temp:
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Step 2. Set up belt ends as per gluing, but do not use paper or stickytape underneath - just the bare metal. It heatsinks the tape very nicely:
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Step 3. Using the tip of the iron, quickly tap the overlap with the tip of the iron about 10 or 15 times as a speckle of small dots. Do not hold the iron on too long or it distorts the belt:
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Final result. Here are seven 220mm circumference belts. Three of these are glued and the remaining four are welded, ready for testing by 80486sx:
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