National RX-5150 motor overheating and not spinning.

[Shazman]

Hello. I live in South Korea. Im new to this forum. I recently got into collecting boombox equipment. About a week ago I purchased a National RX-5150 from "Buyee" a Japanese website. The boombox has been fully serviced by the seller. Including new belts, a complete recap of all capacitors, and lubrication of switches. I was playing some tapes last night and the sound was sometimes slowing down with some "wow" as well. After a while I press the TPS switch and then the motor fully stopped spinning the cassette for playback. I don't know what happened. When I opened the boombox the motor was very hot to the touch. It won't turn on at all. Is not playing any cassettes now. The motor just overheats even when the unit is switched off. I had to take the batteries off to stop the overheating.This also happens when plugged into the wall. I really need help with this. Please if anyone knows why the motor won't spin and just overheats would be great. Thank you in advance.

I attached pictures of the unit. One of the pics shows the cassette working. The open boombox pictures were taking after the unit failed. Also the motor is original and it wasn't replaced.

 

[caution]

Just out of curiosity are you powering it with the voltage listed on the back?

 

[Shazman]

Just out of curiosity are you powering it with the voltage listed on the back?

Yes. I have a stepdown transformer so I can use my Japanese appliances in Korea. Also the boombox was using batteries. The big round ones that it requires.

 

[AE_Stereo]

Most probably the motor shaft is jammed with dried grease/dirt. In the past I have opened and re-lubricated a seized motor of a Panasonic box and it started working smooth.

 

[Shazman]

Most probably the motor shaft is jammed with dried grease/dirt. In the past I have opened and re-lubricated a seized motor of a Panasonic box and it started working smooth.

Oh that sounds difficult. The motor doesn't seem to have any screws for me to open. It seems all sealed up. How can I open the motor to fully clean the shaft and put lubrication? I searched online and I get way too many different answers..

 

[Tinman]

I've done what AE said above but if you don't want to get into servicing your current one, you could buy a replacement.

 

[Shazman]

I've done what AE said above but if you don't want to get into servicing your current one, you could buy a replacement.

I could try to service it. But what are the procedures to opening the motor without damaging it?

 

[AE_Stereo]

Yes, old motors are sealed by pressing the sheet metal body around the end plate. You need to pry open with a suitable tool such as thin flat screw driver or chisel. I did the same. Not that difficult.

 

[Shazman]

Yes, old motors are sealed by pressing the sheet metal body around the end plate. You need to pry open with a suitable tool such as thin flat screw driver or chisel. I did the same. Not that difficult.

Thank you for the tip. Once open do I put a "all purpose" oil inside the motor?

 

[Tinkererman]

I just took one of these apart recently, does yours spin freely?

It's not that easy, or difficult, but there's tiny brush feelers in there. Inside the metal case, there's a Nylon block with the brush holder and the commutator brushes that when the nylon is seated, the brushes ride on the armature, when you wiggle that out, the brushes will come off the armature and spring towars the center a bit. You'll probably find you need a new motor. I was able to find one that works on fleabay.

This is the fleabay search term = 2PCS 530 Motor DC 12V 2400RPM-EG-530AD-2B Micro-motor CCW DIY Parts New

Best bet I'd say, if your motor got that hot, it's more than likely toast. The shaft is a little shorter on the motor above but it works fine.

I think this is the one I replaced in a RX-5250, same motor as RX-5150

Rich

 

[Tinman]

The worst part is getting the brushes back over the shaft and commutator (armature).

 

[Superduper]

Before you "take it apart", first remove the belt and just spin the pulley. If it spins easily, then add some power. 9V should do it. If it spins easily but still does not move on it's own with 9v applied, it's toast. The windings have likely shorted and those aren't really serviceable. There are probably some speed control circuitry on the mini pcb near the back cover but any failure there is not likely to heat the entire motor, that's more likely from shorted windings, excessive load, or seized bearing resulting in heat.

If it does not spin easily, or not at all, you maybe can take it apart and see if unsiezing it can help restore it, but in my experience, these motors should not rely on external lubrication. Otherwise everytime it needs to be lubricated, you will find yourself tearing apart the box again. Instead, the factory installed oilite bearings. These are brass bushings impregnated with oil. When it heats up, the pores open up and release oil to lubricate the shaft. When the motor stops and cools, the oil should reabsorb. You might be able to soak the bushings in oil to see if you can restore the bushings (or replace them with new oilite bushings if you can find the right size. However, again, keep in mind that if putting a drop of oil on the shaft allows it to run smooth, as soon as all the oil flings off, the motor will slow down again and you'll find yourself constantly readjusting the motor speed.

 

[Shazman]

I just took one of these apart recently, does yours spin freely?

It's not that easy, or difficult, but there's tiny brush feelers in there. Inside the metal case, there's a Nylon block with the brush holder and the commutator brushes that when the nylon is seated, the brushes ride on the armature, when you wiggle that out, the brushes will come off the armature and spring towars the center a bit. You'll probably find you need a new motor. I was able to find one that works on fleabay.

This is the fleabay search term = 2PCS 530 Motor DC 12V 2400RPM-EG-530AD-2B Micro-motor CCW DIY Parts New

Best bet I'd say, if your motor got that hot, it's more than likely toast. The shaft is a little shorter on the motor above but it works fine.

I think this is the one I replaced in a RX-5250, same motor as RX-5150

Rich

I haven't taking it the motor yet to see if it spins freely or not. I will try tomorrow since Im off work. I heard that replacement motors are not of good quality since they are Chinese knockoff. But if the original motor is beyond repair I have no option but to replace. Do this cheap motor replacements make the sound of the cassette worse?

 

[Shazman]

Before you "take it apart", first remove the belt and just spin the pulley. If it spins easily, then add some power. 9V should do it. If it spins easily but still does not move on it's own with 9v applied, it's toast. The windings have likely shorted and those aren't really serviceable. There are probably some speed control circuitry on the mini pcb near the back cover but any failure there is not likely to heat the entire motor, that's more likely from shorted windings, excessive load, or seized bearing resulting in heat.

If it does not spin easily, or not at all, you maybe can take it apart and see if unsiezing it can help restore it, but in my experience, these motors should not rely on external lubrication. Otherwise everytime it needs to be lubricated, you will find yourself tearing apart the box again. Instead, the factory installed oilite bearings. These are brass bushings impregnated with oil. When it heats up, the pores open up and release oil to lubricate the shaft. When the motor stops and cools, the oil should reabsorb. You might be able to soak the bushings in oil to see if you can restore the bushings (or replace them with new oilite bushings if you can find the right size. However, again, keep in mind that if putting a drop of oil on the shaft allows it to run smooth, as soon as all the oil flings off, the motor will slow down again and you'll find yourself constantly readjusting the motor speed.

You are absolutely right regarding lubrication. If the motor constantly needs lubrication then it will eventually run out and I will have to take the boombox apart and do it all over again. A very tedious process. I will check if the motor freely moves or not tomorrow since Im off work. Im hoping it can be fix. Everything else on the boombox works. Only problem is the cassette and the tweets are dead.
Also I heard that "Piezo" tweets expired after decades. Some people have replaced the tweets with paper cone ones. I need to find the right size somewhere online.

 

[Tinkererman]

I haven't taking it the motor yet to see if it spins freely or not. I will try tomorrow since Im off work. I heard that replacement motors are not of good quality since they are Chinese knockoff. But if the original motor is beyond repair I have no option but to replace. Do this cheap motor replacements make the sound of the cassette worse?

I haven't had issues with the cheaper knock-off motors yet. My biggest problem is getting all the damn belts on that model, it really $ucks to change those belts in my opinion compared to a lot of other boxes I've worked on

 

[Shazman]

I haven't had issues with the cheaper knock-off motors yet. My biggest problem is getting all the damn belts on that model, it really $ucks to change those belts in my opinion compared to a lot of other boxes I've worked on

Does something I've noticed. The belts seem to very hard to replace. Their positions are a bit awkward. Has anyone changed their tweets? Mine are dead Im getting zero sound off of them. Since they are "piezo" tweets they dont last long. What kind of tweets are recommended for this model?

 

[Tinkererman]

I use paperclips straightened out, twisted together, then bend then ends into proper shapes with hemostats, you need 3 hands to change them, I've gotten so frustrated changing the belts on this one and the RX-5250. All my tweeters still working