Dead main motor on double motor AR-XA

[WaynerN]

Looks like it's made for the European electrical system, the plug on the power supply is different to what we use here in the US of A

They have a US version.....

 

[dogwan]

I grafted a Technics SL-20 motor to a motor-less AR-XA. Only had to do a little modification the top plate. It's a two speed DC motor. I mounted all the control board and transformer in an outboard box. Had to swap 2 resistors to get the speed adjustment pots to be roughly centered when at speed. Have the notes somewhere.

It works like a champ. Speed change at the flip of a switch. Great torque, up to full speed in less than 1 revolution unassisted. Uses stock AR belt.

 

[cmarti]

That's because you AR guys here on AK bragging about how good they are.

LOL

 

[cmarti]

I grafted a Technics SL-20 motor to a motor-less AR-XA. Only had to do a little modification the top plate. It's a two speed DC motor. I mounted all the control board and transformer in an outboard box. Had to swap 2 resistors to get the speed adjustment pots to be roughly centered when at speed. Have the notes somewhere.

It works like a champ. Speed change at the flip of a switch. Great torque, up to full speed in less than 1 revolution unassisted. Uses stock AR belt.

I do own one of those motors with the boards and switch, it came from a JCPenney MCS equivalent of the Technics SL-20. This will be the most cost-effective option for me. Can you provide me with pics of your project and the identifications and values for the resistors you replaced? I already have the motor, two boards and speed switch out the MCS.

 

[gkimeng]

Check the motor with a VOM. If there's no reading, the coil is bad and the motor is FUBARed. If you get a reading it may be possible to rebuild a motor, but there's no coming back from a bad coil.

 

[dogwan]

I do own one of those motors with the boards and switch, it came from a JCPenney MCS equivalent of the Technics SL-20. This will be the most cost-effective option for me. Can you provide me with pics of your project and the identifications and values for the resistors you replaced? I already have the motor, two boards and speed switch out the MCS.

I will try and take some pics tonight and dig out my notes. If I can't get to it tonight it might have to wait until after Xmas due to time constraints. Don't be afraid to remind me.

 

[gadget73]

DC motors sound good on the surface but without a reasonably involved feedback system to maintain speed I expect you'll find it to be far less stable overall compared to a simple AC synchro motor.

 

[dogwan]

DC motors sound good on the surface but without a reasonably involved feedback system to maintain speed I expect you'll find it to be far less stable overall compared to a simple AC synchro motor.

I hear ya'. I've been wowed by DD's before only to eventually get annoyed with the "hunt & peck" micro variations in speed on non-quartz lock decks.

In my case I wasn't really trying to improve on the original AC motor. I just had 3 AR decks at the time in various stages of being rebuilt. It was a fun experiment and a good solution to having a dead motor. However, it does say something that the Technics DC motor was the one I ended up keeping. I don't know if it's more to do with having an outboard power supply and DC motor (read: lack of hum), or the combination of belt with DC motor that makes a very smooth and fun deck.

Giant killer? Probably not.
Happy deck? Oh yeah!

 

[cmarti]

I will try and take some pics tonight and dig out my notes. If I can't get to it tonight it might have to wait until after Xmas due to time constraints. Don't be afraid to remind me.

Thank you dogwan, I was already looking at boxes where I can put the switch selector, power and motor control board. Now how you modified the platter that is something I can't see or figure out.

 

[sfrost]

I have boxes of motors from the two motor version XA tables, probably the easiest way is to just replace the motor.

 

[cmarti]

I have boxes of motors from the two motor version XA tables, probably the easiest way is to just replace the motor.

That is wonderful, I need the silver motor, which is the one you adopt the pulley to. Pic below.

 

[dogwan]

Found my notes. There are two resistors before the adjustment pots. 33k (45rpm) and 47k (33rpm) replaced with 27k and 39k respectively got me about to the middle of the pots adjustable range. The diameter of the belt surface between the SL-20 and the AR are pretty close.

 

[dogwan]

Here are some quick pics of the modded deck. As you can see the motor still mounts in the same opening for the original (this was a 2-motor deck). It just needs to be set back off-center to account for the smaller pulley diameter (runs at higher rpm). Also, I like having the motor mounted on rubber grommets that came out of the SL-20.

Other than drilling the holes for the 3-point mount there were no other modifications necessary for the platter or top plate. Although I did fill the hole left by the original switch and tonearm rest.

Hope this helps. But, it sounds like you've got a line on a stock motor. Definitely the easier way to go!

 

[cmarti]

View attachment 1068981 View attachment 1068982 View attachment 1068983 View attachment 1068984

Fascinating work Dgwan, your skills are impressive! Can you post a picture of the box where you put the power board, switch and motor board?

sfrost is hooking me up with an original replacement motor. The dude is king, you too are one!

 

[cmarti]

Came here to provide a new update, I was able to replace the stock motor with an exact one and everything worked great... until the motor died the same way the old one did.

I ended up installing the Technics SL-20 motor on the directions of dogwan and was able to fit the power motor board inside the table, even the stock 33-OFF-45 switch by drilling the plinth. Everything looks clean, the only thing I left out of the table is the little board which contains the 20 K potentiometers, resistors and diodes I think? I screwed it to the back of the table so for easy access in case I wanted to adjust the speed of the motor for both 33 and 45. Also thinking about upgrading the pots to better ones. I feel like the stock ones are super weak. I did not replace the resistors dogwan mentioned and was able to achieve the desired speeds by adjusting the pots.

I am no longer using the stock switch as it was causing speed variations, the turntable would randomly jump up in speed.

 

[dogwan]

Came here to provide a new update, I was able to replace the stock motor with an exact one and everything worked great... until the motor died the same way the old one did.

I ended up installing the Technics SL-20 motor on the directions of dogwan and was able to fit the power motor board inside the table, even the stock 33-OFF-45 switch by drilling the plinth. Everything looks clean, the only thing I left out of the table is the little board which contains the 20 K potentiometers, resistors and diodes I think? I screwed it to the back of the table so for easy access in case I wanted to adjust the speed of the motor for both 33 and 45. Also thinking about upgrading the pots to better ones. I feel like the stock ones are super weak. I did not replace the resistors dogwan mentioned and was able to achieve the desired speeds by adjusting the pots.

I am no longer using the stock switch as it was causing speed variations, the turntable would randomly jump up in speed.

Cool, now I'm not the only one to do this! Please post pics.

FYI, I was having the same problems with the stock switch before I did the transplant. Pretty common to get corrosion on the traces of those old rotary wafer switches.

My plan is to eventually replace those VR pots too. Going to get some panel mount ones and use flying leads to the PCB. That way I will have access to adjustments on the front of the separate box. However, once set I have found the stock ones (after heavy deoxit treatment) to be really stable so haven't had much motivation.