Nakamichi ca-7a repair

That is not going to be easy, and that will require quite a bit of force. It looks like there is a clutch in there too, so you don't overdrive the pot. I would still look at a high torque model airplane servo with a micro limit switch. Even if you find a worm close securing it to the other driven piece is difficult. Servos are not cheap, but I think they would be better.
I don't understand. Where do see a clutch, and what is a servo with a micro limi switch?
 
The servo is used in model airplane to move control surfaces, but now that I think of it they may require current than you have in the NaK supply. The servos are quite well made and they should give you enough rotation. Google model airplane remote control servos, I think that drive motor is 12 vdc in the Nak.
 
Is the last gear, the one below the broken worm section, broken as well? It looks like the front half is missing.
I'd expect to see as much in front of the wormgear shaft as I see behind it. Is the front half of that gear stripped?

EDIT: I'd Google every part number found on the motor or control. That might turn up something.
 
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Without any part of the original it is next to impossible to throw any old thing in there to make it work. Even if you buy matched sets of gears,they can die early from any misalignment. It looks like you have some room in there to squeeze another drive assembly in there. how hard is it to turn the knob? They sell very small high torque servos for model airplanes. I had one hooked up on my trolling motor to give me remote throttle control for no money, and it worked well on 12 VDC. You have to think out of the box, so to speak.

There are scores of micro-serves for robotics, etc. I believe most are 5v. They have a splined shaft to which there are many possibilities for arms, etc. They turn ~270*.
They would have enough torque to turn the volume control but would stall well before causing damage. They are fairly low current. There might be kits to put a sprocket on the servo and run a Gilmer belt (a tiny toothed "timing belt"). You'd have to MacGuiver a sprocket onto the volume control. Possibly you could use a "O" ring style belt and grooved pulleys?
The biggest problem adapting a servo is the problem of turning a volume control shaft 270* while the shaft prevents using a linkage rod which would need to slice through it.
There are scores of possibilities on this site. You could drive any of these mini-servoes with the signal to the existing volume motor (assuming it's DC and two wires; a simple voltage divider would tune the servo response/speed, assuming supply to original motor is >5V DC.
https://www.pololu.com
 
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I have a feeling that I'm in over my head with this. I thought that I would just be able to (if I found some plastic gears) to be able to fix this. I understand that they wouldn't be exactly the same but there was someone who commented on the FB page of Vintage stereo & Hi-Fi equipment which I posted my nak issue also. This person ordered a bunch of plastic gears and struck gold in his quest of fixing his Nak gear problem. He did mention clutch work in which I didn't understand. I'm going to keep at it and see where it goes. I really don't have anything to lose, I couldn't use the remote anyways.
 

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Is the last gear, the one below the broken worm section, broken as well? It looks like the front half is missing.
I'd expect to see as much in front of the wormgear shaft as I see behind it. Is the front half of that gear stripped?

EDIT: I'd Google every part number found on the motor or control. That might turn up something.
No, the gear below the worm gear that is on the volume shaft is not damaged at all. Neither is the worm gear that is attached to the motor shaft.
 

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No, the gear below the worm gear that is on the volume shaft is not damaged at all. Neither is the worm gear that is attached to the motor shaft.
Hi Mike,

I see this as a totally mechanical repair. Looking at the pics, if this was mine, once I found a worm gear with the correct thread size, not necessarily diameter at this point, though that would also be great, I'd drill it out to slip onto the existing drive shaft if there is no hole already. Don't glue anything yet, slip it on the shaft to check and adjust length etc...until satisfied with the test fit. Then sand down the worm gear teeth to the proper diameter to sit in to the volume shaft gear. I'd do this with the gear on a drill to spin it as I sand it down to the correct diameter to sit in the volume gear properly. Let's hope the gears you bought have one, or a couple that fit in case you need to try it a couple times. After you are satisfied with the fit, use JB Weld to glue the gear to the existing remaining gear shaft. Obviously you'll need to clean off all the old grease for the JB Weld to hold.

Glenn
 
Hi Mike,

I see this as a totally mechanical repair. Looking at the pics, if this was mine, once I found a worm gear with the correct thread size, not necessarily diameter at this point, though that would also be great, I'd drill it out to slip onto the existing drive shaft if there is no hole already. Don't glue anything yet, slip it on the shaft to check and adjust length etc...until satisfied with the test fit. Then sand down the worm gear teeth to the proper diameter to sit in to the volume shaft gear. I'd do this with the gear on a drill to spin it as I sand it down to the correct diameter to sit in the volume gear properly. Let's hope the gears you bought have one, or a couple that fit in case you need to try it a couple times. After you are satisfied with the fit, use JB Weld to glue the gear to the existing remaining gear shaft. Obviously you'll need to clean off all the old grease for the JB Weld to hold.

Glenn

Totally agree, providing you can source a worm gear with the right pitch, etc, which is a good possibility. Maybe the last part isn't right? Looks to me that the shaft is stationary so can't glue to shaft. If so, you'll probably want to find some tubing that will fit over the shaft that you can drill out the gears to fit. I'd use steel tubing for it's stiffness. Certainly not a good bearing, but packed with grease will last forever. I would't look for an interference fit-too much risk of cracking the original gear. I'd go next bigger drill size and connect the two gears like Glenn suggests. Cut off ends @90*; you could put a number of serrations in the ends with slight hacksaw cuts so the union transmits torque without breaking apart. Gluing plastics is always a shell game where adhesion is concerned.
 
Totally agree, providing you can source a worm gear with the right pitch, etc, which is a good possibility. Maybe the last part isn't right? Looks to me that the shaft is stationary so can't glue to shaft. If so, you'll probably want to find some tubing that will fit over the shaft that you can drill out the gears to fit. I'd use steel tubing for it's stiffness. Certainly not a good bearing, but packed with grease will last forever. I would't look for an interference fit-too much risk of cracking the original gear. I'd go next bigger drill size and connect the two gears like Glenn suggests. Cut off ends @90*; you could put a number of serrations in the ends with slight hacksaw cuts so the union transmits torque without breaking apart. Gluing plastics is always a shell game where adhesion is concerned.
Ah, yes, the shaft is probably stationary and the motor gear spins on it. Squaring up and notching the butt joints is a good idea, and with gluing plastics, that's why I suggested JB Weld. That stuff is amazing and cures rock hard.
 
Glenn, i don't think you have worked with worm gears, they really have to fit well together so they don't self destruct, and the stub piece you want to glue to with the fine gear on it has teeth missing. The other Nak motorized pots are not done like this. Nakamichi is gone.
 
Hey Mike,

Did you check with Nakamichi for parts?
Glenn, you can't find these parts anywhere. Believe me, I've been searching the internet for weeks. I ordered a whole bunch of small plastic gears. They're very inexpensive which is good. I keep wondering if Nakamichi used the same type of mechanics with any of their receivers of that era.
 
Hi Mike,

I see this as a totally mechanical repair. Looking at the pics, if this was mine, once I found a worm gear with the correct thread size, not necessarily diameter at this point, though that would also be great, I'd drill it out to slip onto the existing drive shaft if there is no hole already. Don't glue anything yet, slip it on the shaft to check and adjust length etc...until satisfied with the test fit. Then sand down the worm gear teeth to the proper diameter to sit in to the volume shaft gear. I'd do this with the gear on a drill to spin it as I sand it down to the correct diameter to sit in the volume gear properly. Let's hope the gears you bought have one, or a couple that fit in case you need to try it a couple times. After you are satisfied with the fit, use JB Weld to glue the gear to the existing remaining gear shaft. Obviously you'll need to clean off all the old grease for the JB Weld to hold.

Glenn
I wasn't going to set anything permanently until I'm sure it'll work.
 
the stub piece you want to glue to with the fine gear on it has teeth missing. .

Delete all my comments about fabricating a new gear. Without the mate on the worm gear, the pooch is well and truly screwed!
You still might turn up a solution at the servo and robot site I linked. There's a lot of room without the existing stuff and motor.
You could compromise and use a servo with a connecting link to an arm on the volume shaft but it would only drive the control <180*, which might be more than you ever need/use? At least it would be (relatively) easy.
 
Gears are turning (punintended!). The myriad of mini-servos turn ~270*, about what a pot does.
They are easy to mount, or fabricate something they'll mount to; getting one parallel to the gear on the volume shaft would be quite doable.
A little (about the size of the gear on the volume control) V pulley should be very simple (got an erecter set handy?), then an "O" ring belt across the two. If you want to be fancy, take a triangular file to the teeth and make a V for the belt to increase traction.
A dropping resistor if needed to match voltage or even lower the speed, and done.
I fabbed a deal with a lineage rod and one of these servos to switch my home generator honor off to save fuel during emergencies. The serves are like $10.
Go for it.

EDIT for clarity: These servos are gear reduction with a tiny motor. Even so, they move pretty fast while having good torque. There are several sizes/torques, but you shouldn't need a lot. I'd just get a small one and try it out. If you got it working and it wasn't strong enough, you would have a good idea where to land for resizing.
They also have a 3 wire position sensor, so 5 pins, but for this app, not needed, just +/- motor wiring.
 
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Glenn, i don't think you have worked with worm gears, they really have to fit well together so they don't self destruct, and the stub piece you want to glue to with the fine gear on it has teeth missing. The other Nak motorized pots are not done like this. Nakamichi is gone.
I haven't per se, but I built and flew R/C model airplanes for more that 25 years. We were always modifying parts to suit the needed function. I totally understand worm gear function and fit. That was where my thinking was regarding modding the worm gears diameter to sit in the volume gear grooves. I'm not saying it's an easy task, and with the gear teeth missing on the small gear it's a mute point. Maybe Mike will luck out and there will be a parts unit out thereat some point.
 
I haven't per se, but I built and flew R/C model airplanes for more that 25 years. We were always modifying parts to suit the needed function. I totally understand worm gear function and fit. That was where my thinking was regarding modding the worm gears diameter to sit in the volume gear grooves. I'm not saying it's an easy task, and with the gear teeth missing on the small gear it's a mute point. Maybe Mike will luck out and there will be a parts unit out thereat some point.
Well Glenn, if I can't figure it out I'll let you take a crack at it (if you want to). I'll barter you for a beautiful pair of 1590's. LoL!!!
 
Well I have a match. I had to replace the original worm gear from the motor and got a match with a motor gear that is attached to the horizontal rod. Now to find a worm gear that will fit the gear that's on the volume shaft. Time to order a bunch of different sizes of worm gears.
 

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Amazing! I never imagined you'd find a gear with same diameter and pitch!

Where did you find it and how?
 
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