Late last year, I picked up a Magnavox D8443 boombox. I bought it because I used to own one back in the 80's, but my original version had long since broken down and I eventually got rid of it.

The one I purchased now has that somewhat common "broken gear" issue in the cassette deck. Not one for letting that stop me from using the cassette part of the boombox, I started looking for a repair solution.

After discovering the rarity of the gear, and the difficulty in salvaging a replacement from other devices, I decided to fabricate one of my own. Through several attempts, I believe I have a working solution, an honest to goodness replacement gear!

I installed it last night and have played six full tapes in it (front and back). So far, so good. I want to run it often over the next couple of weeks to test for durability and wear. If all looks good after that time, I'll be satisfied with the solution.

I understand that the "broken gear" is a common issue with these boomboxes. So, I'd like to gauge interest in others wanting to acquire replacement gears of their own. I am able to get these mass manufactured, but as with anything else which is custom manufactured, the economies of scale will keep the prices down.

I'm going to be compiling a video, documenting the repair process, in the near future. There are some delicate steps involved with replacing this particular gear. But I believe people would want to restore their broken D8443s to original if the opportunity presents itself.

I attached a still picture from the video, showing the replacement gear in place. It is the bright white gear in the lower half of the image.

Thanks,

Jeff

VintageVolts.com

Nice project! I have two of these boxes with broken gears and started a simulair project. Did you consider to replace both helical gears for normal spur gears, as they much easier to fabricate?

Looking forward to see more of your project!

I decided to leave them as helical gears. Some of the major advantages to helical gears are quieter operation and strength compared to spur gears. There is little chance of "sloppy contact" between helical gears, and the angle of the teeth effectively make them "bigger" and more resilient to damage.

Right now, I have played over 40 tapes, both sides, on the gear I installed. There was not a single problem with the tape operation since I installed the gear. I have yet to open up the case again to see if there is premature wear on the gear. I plan on doing so this weekend.

Very nice, looks like its holding well! I want to get rid of all weak gears, so going to experiment with spur gears. Think you are right about the extra noisses though. What kind of material did you use? 

It's nylon based, built up using an additive process, I had a chance to utilize some advanced 3D printing using the original broken gear as a model.

When I'm happy with the final design, I'm going to negotiate the cost for a run of these to get some made for a decent price.

Nice to see that it's possible to make with a 3D printer! I got access to an old MakerBot, but have no idea how it works. Don't even know if the machine stil works... It suppose to make itself (the machine) and has some gears in it. But they are kinda large compared to our cassette gears. But I think your gear will hold well, cause the material is quit good I've heard.

I'm not sure if a Makerbot has a high enough resolution to recreate the gear. There are over 35 angled teeth around a diameter of 1 inch. The helical gearing needs to stay because the part it meshes with, the large flywheel, is molded with the matching helical teeth. I had considered investing in a 3D printer myself to make the gear, but opted not to because of the amount of detail I expected I would have needed. Not that I wouldn't want a 3D printer of my own, anyway!

i also wasn't sure if the ABS or PLA material would be strong (not brittle), yet pliable enough to withstand the tensions that occur during continuous tape operation. Instead, I just "tapped my resources" so to speak for an alternative solution.

Im also afraid that the resolution of the Makerbot is not high enough. It is indeed a really  complex and small gear. I've been searching the net and it seems impossible to find a gear with the right diameter, amount of teeth and the strange tooth angle of 30 degrees.

The part the broken gear drives is the clutch of the cassette spindle. I have just dissembled it and it looks like it could be possible to make a repro spur gear with a lasercutter. I have acces to such a machine. Biggest problem is the adjustable spring for the clutch tension. Im thinking of a redesign with a magnet like they did in the Sony DD series or just make one setting for the spring. It is a nice problem to solve this stupid broken gear 

Jeff,

My Dad recently found this in our garage after I had asked him if we had any large 80′s style boom boxes. It worked great for about a week when recently, maybe just 2 days ago, the cassette tape would be chewed up into the pinch. After toiling over what could be wrong I have finally figured out it’s exactly the gear problem you’ve spoken about in this article and on your stereo2go forum post.
Is there anything I can do to get a hold of one of those gears you made cuts of? Also, is it true I can use the RCA output on the side as an aux jack for my iPhone/iPod?

Bret,

I'm probably going to have a handful of them manufactured. That way, if people need them they can purchase the gear from me, directly.

Still working out when I can have them made and how much they will cost to have done, but my target price for one of the gears is $15, delivered to USA addresses.

The RCA jacks on the side are "line level" inputs and should work fine with any iPod type device, or other music player with a headphone jack. You'll just need to be careful turning the volume all the way up on the music device as it might overdrive the input on the boombox.

The best thing to do is listen to a radio station and set the boombox volume to a comfortable listening level and leave the volume control where it is. Then, with the volume completely down on the music device, switch to that input on the boombox and slowly increase the volume on the music device until the sound out of the boombox closely resembles the volume you heard from the radio. Then you can use the boombox volume control to adjust the sound volume for listening. Remember that volume setting on your music device for use in the future.

Remember, the current clutch design allows for the auto-stop feature when using FF and REW (something many tape players normally lack). Hopefully, your redesign can mimic that same action.

After three weeks of running tapes through my D8443, I'm happy to say that the replacement gear is holding up very well.

During the time I was playing tapes, I ran 2-3 full tapes through each day. I have not heard a drag or any other anomaly in the sound the whole time which would otherwise indicate a broken, stripped, or non-meshing gear.

I am now going to try and secure a chance to get a bunch of these manufactured, after which I will make them available for purchase.

I attached a picture of the gear as it looks after this three weeks of use.

Nice! If you manage to make more of them, I'll take an option for two!

Please note that this is ONLY about the gear which is located under the belt driven flywheel, having helical teeth, and not the other gear which tends to break. The other gear is on the side near the tape counter mechanism. I will probably be designing a replacement for that one someday.

I've ordered a small batch of replacement gears, but I don't expect them to arrive until early-to-mid April, after which, I need to ensure the center hole is drilled to the proper size and diameter. I kept the initial batch small in case they don't mass manufacture as well as I expect. I don't want to lay out a lot of money for potentially defective items.

I'll provide actual sales pricing after I get the replacements and check for manufacturing quality. Until then, fellow D8443 owners, please be patient while I wait for delivery of the replacement gears!

Jeff

very noble of you Jeff

My shipment of replacement gears were manufactured sooner than I expected. I posted information and an eBay link in the "Boombox eBay Auctions" forum.