Inside the Thorens TD-16X Motor

[tnsilver]

This is a later low voltage (16 - 20VAC) asynchronous motor that's fed from a wallwart power supply, where voltage for one winding gets 90° phased by a 4.7μF capacitor. It's common on the latest marks TD-160, TD-165, TD-166 and possibly some TD-14X versions. There's no shunt resistors in this configuration (as opposed to the older 110VAC motors of earlier marks).

The owner, an overseas colleague of mine, said it makes a grinding noise, that it warbles and reluctant to start, and that sometimes it spins in the wrong direction. He said that a mechanical load on the pulley makes it switch rotation direction or stop altogether. I've confirmed most of this with an external power supply,

The good part is, my buddy said he has a replacement motor, so I can do whatever I want to it, fix or ruin it, he doesn't care but still wants it back if it's fixed. Well, OK, it sounds like lot's of fun anyway...

Let's get to work:

Removing the 3 motor mounts that also serve as locking pins isn't easy. I had to drill them out. The plastic cover over the 4 wiring terminals is easy to extract with a flat screw driver, and the pulley comes out with the aid of a 1.5mm hex key:

EDIT: I was just informed it's actually a 1.27mm hex key. Good to know!!!

Here's the split open motor with the bottom part of the housing on the left and the magnet rotor on the shaft with the upper housing. Notice the grind, which I initially mistook for gunk, on the lower bronze housing of the self aligning shaft bushings:

The white nylon (or teflon) spacer washer came out very easily with a pair of long pliers. Notice the end of the green plastic rotor core. It's recessed, and different from the other end. It has a polarity and it won't fit back the wrong way:

Then, the rotor slid out, almost too easily, which was suspicious. I'll get back to it soon, but notice the exposed shaft bearing. It's a miniature version of the TD-124 E50 motor self aligning bronze bushings, only in this case the housing is press fit and I dared not tamper with it:

Here's a better picture displaying the grinding on the bronze bushing housing on both ends of the shaft. Notice the flat square recess at 2/3 length of the shaft. It's intended to go against a tiny round bulge inside the plastic rotor core central bore. I had a look inside and that little bulge was dangling loose, so the entire rotor could easily swing back and forth along the shaft for the few fractions of an inch the grind housing would allow:

I couldn't help but display the 2 motor winding for you guys, so I spread them on their core for as far as I dared, just to take the following pictures:

So basically, these are the main static parts of the motor:

OK, so here comes the fix...

 

[tnsilver]

First, I had to sand flat the shaft bearing housing. It's easier said than done b/c those spikes from the metal cover seriously restrict access. Naturally, I had to clean it too and soak it for a while in 3 in 1 oild for the sintered bronze to suck in some lubricant.

Then, I had to solve the gap issue. It's the same gap issue that causes the motor to knock and requires the famous anti-knock kit. In this case however, the grinding of the shaft bearing housing was real bad.

I'm pretty sure that at some point, the pulley got hit from straight above, or that some clueless clown pulled real hard on the pulley base (press fit on the shaft) to replace or remove it. In any case, exerting these vertical forces on the shaft caused the rotor to slide on the shaft, break the retainer bulge and get misaligned between the winding. It also created too much pressure between the original stainless steel washers that are fit at each end of the shaft against the bronze bearing housing. Gradually, the stainless steel ate it's way into the softer bronze. This probably happened in the upper part first, then, some leverage was created, the rotor shaft sank, and the stainless steel started eating at the bottom housing.

Anyway, that motor got too much gap that caused the grinding noise and a capricious rotor shaft with a loose magnet is accountable for the rest.

So I was thinking about restricting the shaft gap to the bearing housing on both ends with thin washers. I collected a few that I had handy. The upper shiny ones are the stock stainless steel spacers. The ones on the bottom are5mm teflon washers, which I wanted to use, but were just too wide. The other washers are from my cart mounting accessories. I ended up using just the stock stainless steel plus the thin (non-springy) washers 2nd from the top:

One washer went on each side of the shaft, under the stock stainless steel spacer:

OK... That turned out to be a pretty easy fix! I'm surprised. All I had to do next is close up. Fortunately, that motor housing got a set of extra holes in it's *ears*, so I could utilize those to shut it all tight with some screws, nuts, washers and loctite.

Note: Before tightening those three new screws, I had to align the two housing parts with the middle winding core and the rotor. This is very similar to aligning a TD-124 E50 motor, only much easier. This motor is small, fits in a palm and uses low feed voltage. I just had it hooked to a 16VAC power supply, held it in my hand and gradually tightened the nuts while aligning the motor parts to generate the least amount of vibrations and noise.

In fact, this went so well, I could not tell if the motor was spinning while holding it in my hand. It was spinning so quietly, I had to look at the pulley to make sure it's turning. I was happy!!!

The only caveat is I was too lazy to drill and tap the old motor mounts and find small enough screws to go and lock them on the motor housing. I wasn't even sure if it's possible. Luckily. I trust JBWeld to cover up for my lazyness:

So it now, looks like this:

...and it runs perfect! Too bad I have to send it back.

 

[Fluffer]

Long term lurker here, and a bit shy to post, but I got in touch with tnsilver through a Conversation, and he's encouraged me to publish what I wrote to him, saying it might be useful to others.

Here we go, go gentle on me!

"I wanted to thank you so much for giving me the courage to open up the motor from my Thorens TD160C, having read your very detailed post above.

My deck is an early S/N (07....) UK mains powered (no wallwart) 50Hz model and the motor is slightly different inside from the later one that you were sent by your friend. Manufacture stamp on the motor is July 1973. I bought the deck from the original owner, who paid £54.12 for it and £11 for the Shure M75ED2 in early 1974, and I have the receipt!! The caps were the original ones, namely 0.15uF phase and 0.0022uF suppressor, and, after all the usual servicing and lubing of a pristine stock 45 year old deck, I was still getting persistent motor grinding noise and vibrations and an irritating 100hZ hum. I tried changing the caps (no difference) and installed the SRM Thrust plate below (some difference), but still not enough. The spindle was completely straight. Also the original rivets on the mounts had become loose whilst tightening, so azimuth adjustment was shot.

And then I found your posting! On opening up I too discovered the burring on the brass bushings at both ends, and cleaned them as you did. The rotor was like yours but used just two small washers at each end of the spindle (no white plastic cylindrical washer), the bottom end having one thin teflon washer nearest the bearing, plus the metal one. The spindle had the same indent. The two coils were both wrapped in yellow tape and seemed intact. After soaking the bearings overnight and a good clean all round, time to reassemble, which was easy to align as you said, though I noticed that the small bearings move inside the bushings, but seem to straighten up when the whole motor is put together. First test...bliss, quiet at last!

But I was not confident of rebuilding the motor mounts like you did. I found a chap on eBay who sells a kit that enables reassembly (search for user 'myach' and 'Thorens Sonceboz'), and a tighter fit than rivets. One thing I have informed the seller of is that the T8 bolt he uses is too long inside the brass Hex spacer and meets the Thorens motor mount screw from the plinth above, so I have simply added 2 x M3 washers + the original Thorens one on the plinth, and now it clears. I've also informed him that the Azimuth spring gets stuck on the nut and is impossible to turn, so I may well use JBWeld with the original mounts, and use his kit to tighten the motor plates. At the moment, my Azimuth is spot on, so I'll stay as is.

So now, thanks to you, at last I have a silent, lubed and rivet-free motor. It took me a long while to get there, but once I'd found your post, I was off! I hope you find my info useful / interesting. I always look out for your postings on Audiokarma on all things Thorens, and am very grateful to you for your knowledge and advice (caps and resistors aswell!).

Greetings from across the pond in the UK, and looking forward to your future postings.

Best wishes,

Guy"

Addendum: Apologies for not taking better or more pics of the rotor, spindle and washers. If I reassemble the motor with JBWeld I will update the photos of inside. The first photo here shows the burred bushing, partially cleaned, the second cleaned, the third just before reassembly, bottom plate/bushing out of shot. I was advised that oiling a sintered bearing was useless, it should be vacuum oiled, but cost was prohibitive, and sewing machine oil seems to have worked well.

 

[tnsilver]

Welcome to AK Guy, it's great having you share this. This is not an easy fix (kinda 'last resort' before buying another motor)) and I'm glad it worked out for you. Kudos for the courage and the great execution.
Thanks for posting those 110V motor inside pics. They're quite rare. I've only seen this done once by a poster on the analog department, and he just soldered a broken winding terminal lead. It's very encouraging
to know those are fixable when push comes to shove. Nice work!

 

[Fluffer]

Thanks for the welcome, Tom. I considered buying another donor deck, not cheap nowadays even in bad condition, just to get another motor. But then there was the possibility of that one being faulty. So your post was very encouraging to try it myself for very little outlay. Drilling out the first rivet was a bit daunting, but once done, it was onward and upward. Really happy with the result. Many thanks once again.

 

[bimasta]

Well done! Luckily I have a spare motor, NOS, for my TD-125. Unluckily, I loaned the TD-125 to a 'friend' who now says it's his. So, a great new motor, with no TT to put it in.

I had to do much the same breakdown, analysis and repair of a Mercedes Marine Diesel engine on a sailboat in the middle of the south Atlantic — the starter motor was effed. There were no stores to buy washers, gaskets et al because we were halfway between Rio and Cape Town, 2000 miles from land. All new replacement parts had to be made from metal cannibalized from other parts of the boat, and reshaped to fit in the starter motor. The tools on board were limited: screwdrivers, spanners (it was a UK boat), files, hacksaw and a few blades, drill-bits and a hand drill. All were covered in rust — it's wet out there on the ocean. The first thing rust attacks are the smallest steel surfaces, so all cutting-edges on sawblades/files/drill bits just crumbled when used, and needed constant resharpening.

The avatar photo shows the pinion gear I made; it engages the ring-gear on the flywheel of the main engine and starts it turning. It needed a 1/2" hole to mount on the shaft, with a hand-drill, through an inch-thick piece of brass. And it had to be 'true' — 90° — 89° or 91° wouldn't do. Took a week, sixteen hour a day just for that hole. Cutting the teeth took another week.

The rumble/wow/flutter specs for that motor were the worst ever — when we tried it the noise was deafening as the far-out-of-tolerance parts clashed. Molten blobs of white-hot metal spewed out. But it got the engine started. The photo is from a Cape Town newspaper, so we ultimately got there.

 

[Grbluen]

I missed this the first time around! Great job!

 

[user510]

Great thread. Finally we begin looking at motor repair! I have a TD150 mkII motor that needs help. When I get into it, I'll share to this thread.
-Steve

 

[batkovan]

Great thread with many photos and explanations that I was constantly checking during my repear.
I will post here to add to the motor variants.
TT Thorens 166 mk II with a motor from '77 which also was knocking. So I did pretty much the same as you guys.
Drilled the rivets careful out >>

Opened the motor and ordered new 17mm spacers

I only needed one extra very thin washer and decided to put it underneath between the plastic and the steel washer. The original steel one >>

The outer diameter of the washer was 5mm and the inner little bit over 2mm(say 2,1mm). I had 2mm washers but with smaller outer diameter so I decided to make one from a 5mm steel shaft from a broken motor that I had for spair parts. I tried to cut a 1mm thick piece with a handsaw as precise as I could and then filed it down to about half a mm, from there on I've sand it down with waterstones(gritt 1000,2000,4000) and finished it with metal polisher... two times because the first time it turned out to thick still and the spindle of the motor was struggling when rotating by hand. The second time was perfect fit almost indistiguishable axial movement of the spindle and effortless rotation. Since I don't have a 2,1m drill bit I've grinded slightly with a dremel bit the inner diameter until it fitted the spindle perfectly.
Still not as shiny as the original(below)

it turned out maybe a fifth from a mm>>

I polished with metal polisher the bottom bearing and also the two sides of the stacked parts of the motor housing>>

the motor before putting back together >>

Cleaned the bottom bearing with ethanol and then let it overnight in sewers oil. I puted a drop of paraffin wax/ medical parafin on the outside of the motor bottom bearing to seal the motor (it will probably fall of).
The elongated nut/hex spacer 17 mm mounted and the housing closed the next day>>

I had to sand little bit the edges of the spacer with the azymut spring in order to fit in. And the motor was mounted back in the turntable.

 

[vinylrayk]

Excellent info, guys! Thanks for sharing your experience and photos. Should be applicable for my TD-125 motor, too.

Ray K

 

[tnsilver]

Should be applicable for my TD-125 motor, too

probably is if it's a Mk-II. You know, I hate to discourage anyone from having a go at a fun project in this COVID-19 boredom season, but keep in mind this can turn sour in a blink. Opening up these motors is kinda risky. If it's just knocking, which is a well-know and documented issue, Vinyl Nirvana offers an affordable risk free anti-knock kit that will fix the problem 100%. Just sayin' sometimes it's better to resist the urge and do the smart thing...

 

[ahsketch]

Great thread. Finally we begin looking at motor repair! I have a TD150 mkII motor that needs help. When I get into it, I'll share to this thread.
-Steve

Hi, did you ever get inside of your 150 mkII motor?

 

[user510]

I've been thinking of other things of late. That motor awaits me in the box with my other Thorens motor stuff. Thanks for the reminder. This thread is indeed inspiring.
-Steve