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Old 08-31-2018, 10:33 PM
stragulus stragulus is offline
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RCA VDT-350 mechanical issues

I have a RCA VDT-350 that has the dreaded cracked loading gear. I've been able to jury-rig it with a lot of effort but now the loading arms work as expected. However, I'm having a hard time with the operational keys and the picture stability.

With the plastic lid on the tape holder, I can get the deck to play and rotate the reels. However, the bottom half of the picture is white noise. If I leave the lid off and press on the tape in certain locations, I can get a full and good picture, usually then the take-up reel doesn't rotate though so it will be for a brief moment. But at least the heads seem alright.

Additionally, the keys are sometimes locked. It's not an issue with levers directly underneath the keys like this guy describes on youtube: https://www.youtube.com/watch?v=WLNaLWqLy48

However there is a part of the mechanism I can move with a screwdriver that will lock some keys but not others. I'm not even sure if that part is supposed to move. At this point it just becomes a whole bunch of guesswork. Does anyone have a copy of the service manual for any of the VCR's that share this mechanical chassis? I think it's the same as the original VCT200.
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Old 09-04-2018, 08:05 PM
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TinCanAlley TinCanAlley is offline
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I have the exact same unit. When my gear cracked, I had a mold made of it and made one plastic and one metal. Wish I had save the mold, though. The plastic didn't last long, but the metal one has been in service for about 5 years.

I saw the exact problem you are. When you put the assembly back, you have to hold the arms together as you insert the gear. If they are off by even one tooth, the keys will lock. I had the keys lock and then figured it out, so once I got the keys unlocked, it worked like a charm, so I can't say whether having it off a tooth that allows it to sometimes play whether that would interfere with the video reproduction. Did you remove the head assembly to get to the gear? If so, is it back in correctly?
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Old 09-18-2018, 09:40 PM
stragulus stragulus is offline
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Thanks for your answer. Yes you are right, it is an alignment issue of the arms. While my rigged gear kind of works, it has enough play in it that the arms did not move synchronously enough. I have yet to create proper replacement gear.

What did you use to create the gears? Especially the metal one I'm curious about. Given how much force is placed on that asymmetrical shaft hole of the cracked gear, it's bound to fail again with materials that can deform. Maybe nylon would work (that can be 3d-printed) as the original is also nylon, but I'd rather create a metal one. I have a 2d design made with inkscape that has the right amount and shape of teeth, I have yet to turn that into a 3D design (sketchup?) and then I suppose it could be 3d-printed, but does that work for metal or are there other solutions? I don't have any fancy equipment for this though I suppose I could find a workshop in my area.
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Old 09-19-2018, 12:23 AM
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Electronic M Electronic M is offline
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AFAIK there is no metal 3D printing method that costs less than the average house.
You may want to take the old gear and make a silicone mold of it...You can then cast a new one out of wax and take the wax duplicate and make 'lost wax casting' duplicates out of lead, aluminum or some such metal.
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Old 09-19-2018, 05:38 PM
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TinCanAlley TinCanAlley is offline
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Quote:
Originally Posted by stragulus View Post
Thanks for your answer. Yes you are right, it is an alignment issue of the arms. While my rigged gear kind of works, it has enough play in it that the arms did not move synchronously enough. I have yet to create proper replacement gear.

What did you use to create the gears? Especially the metal one I'm curious about. Given how much force is placed on that asymmetrical shaft hole of the cracked gear, it's bound to fail again with materials that can deform. Maybe nylon would work (that can be 3d-printed) as the original is also nylon, but I'd rather create a metal one. I have a 2d design made with inkscape that has the right amount and shape of teeth, I have yet to turn that into a 3D design (sketchup?) and then I suppose it could be 3d-printed, but does that work for metal or are there other solutions? I don't have any fancy equipment for this though I suppose I could find a workshop in my area.
I gave the gear to a friend that had a kit he uses to cast parts for his models. This was the first large size cast he had done. I'll get a hold of him and ask.
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Old 09-23-2018, 09:39 PM
stragulus stragulus is offline
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I just attempt to create a 3D model of the gear using a blender tutorial and a calculator. It would be $5 for plastic (nylon) and $15 for steel. I haven't been able to shape the shaft correctly just yet though, but it gives a reasonable idea about pricing.

There is also a bigger gear in the unit that has the same problem but to a lesser degree (it's on the other side of the same axis). That too looks a little worn out and has a minor crack. It's much bigger though. I'm going to see if I can get the small one working first using the 3D model.
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Old 10-06-2018, 09:07 AM
stragulus stragulus is offline
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Designed the gear with flattened shaft hole and had it 3d-printed through shapeways. The hole was a little too tight but with some filing and hammering it fits great now and works great too!





Tracking of the picture seems off, but I'll save that for another post.
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File Type: jpg 20181005_213730.jpg (50.0 KB, 17 views)
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