Thorens 125 MKII problem

rcag_ils · « **on:** 2 Jan 2010, 11:17 pm »

Well, the belt on my 125MKII slipped off the pulley during every start up, and stop. A loose belt, I thought. After purchasing the most correct Thorens belt, the belt stay on the pulley just fine.

But I've noticed a knocking noise coming out of the motor while it's turning due to the tighter new belt. Although the knocking noise doesn't get transmitted thru the chain and to the speakers, I am suspecting the motor bearing is going bad, (yes, I oiled it, no help).

Now instead of paying OL $699.00 for a motor kit, is there any cheaper alternative? (used good Thorens motor is hard to come by). I like the platter bearing on this table, very, very quiet.

Wayner · « **Reply #1 on:** 2 Jan 2010, 11:50 pm »

Newer replacement belts are sometimes not the correct length. This is putting a large strain on the motor shaft and may actually be bowing it. I had this happen with a belt that I had bought for my Empire. Then I got a better (and more expensive) belt and the problem went away. If you hear a noise from your motor, you are doing damage.

Wayner

rcag_ils · « **Reply #2 on:** 3 Jan 2010, 12:27 am »

When I just got my Empire 598, it came with a too short of a belt, the sound from the record "twine" a little bit, but the motor didn't make any noise, I heard it right away and replaced the belt immediately, and it has been working fine ever since.

About this Thorens, I've tried quite a few belts already. I understand what you said about new belt with incorrect length would put stress on the motor. But now I am to the point that, if the belt is too loose, the motor doesn't make noise, but the belt slips off. When I put the correct belt (so the seller says) on, the motor makes noise, but the belt stays on the pulley.

Unlike other pulleys, the pulley arrangement on the Thorens doesn't keep the belt on, otherwise the belt with less tension would have worked.

The Thorens 125MKII motor shaft has a clutch system that I never unstand how it works. It makes a rattling noise during start up, but the noise go away after the motor's up to speed, then the knocking noise kicks in.

PS, the motor doesn't make noise with the belt off, so the motor should still be good.

orthobiz · « **Reply #3 on:** 3 Jan 2010, 03:29 pm »

I don't know the answer but maybe vinylnirvana.com would field your question...

Paul

srb · « **Reply #4 on:** 3 Jan 2010, 03:50 pm »

Quote from: rcag_ils on 3 Jan 2010, 12:27 am

PS, the motor doesn't make noise with the belt off, so the motor should still be good.

If the motor makes no noise with the belt off, that doesn't necessarily indicate that the motor is good, particularly with a vertically oriented shaft. The fact that any load applied to the shaft (short of almost no load where the belt is slipping off) results in bearing noise seems to indicate that the motor bearings might be bad.

Or it could be a problem with the internal clutch mechanism that is making noise.

Steve

Nels Ferre · « **Reply #5 on:** 3 Jan 2010, 05:30 pm »

I have never used a 125 but this may be of help. The motor on my SOTA became noisy at start up. (The noise did not transmit through the system.) As the motor warmed up, the noise stopped. I thought it was a sign that the motor was going. I called SOTA and it turns out there is a motor adjustment access hole underneath the chassis. I hung part of the turntable off the side of the stand, fired it up, and used a thin flat blade screwdriver to make the adjustment. Worked like a charm.

You may want to look at the underside of the Thorens and see if there is an access hole underneath the motor.

Scottdazzle · « **Reply #6 on:** 3 Jan 2010, 06:41 pm »

I had a TD 125 until about 2 years ago. Many replacement belts for this tt were a little too tight and put too much pressure on the motor shaft. I tried 3 vendors and finally found a belt that fit correctly... and no more noise. My recollection is that the $25 belt was worth the cost. I wish I could remember the vendor that I found online. Hopefully, the right belt will solve your problem.

BillWay · « **Reply #7 on:** 3 Jan 2010, 07:23 pm »

The knocking can come from a misadjusted generator board. Get the service manual for the table (I can send you one if you need it) and do the electrical adjustments on the board. It's easy - you just need a multimeter, a small screwdriver, and about 15 minutes. Note that you need to go back over the adjustments a few times, as each change you make in one pot affects the others.

Wayner · « **Reply #8 on:** 3 Jan 2010, 07:30 pm »

Quote from: Scotthobby on 3 Jan 2010, 06:41 pm

I had a TD 125 until about 2 years ago. Many replacement belts for this tt were a little too tight and put too much pressure on the motor shaft. I tried 3 vendors and finally found a belt that fit correctly... and no more noise. My recollection is that the $25 belt was worth the cost. I wish I could remember the vendor that I found online. Hopefully, the right belt will solve your problem.

Was it LPGEAR? They have done good for me in the past with Empire belts, tho expensive ($30).

Wayner

Scottdazzle · « **Reply #9 on:** 3 Jan 2010, 07:38 pm »

Quote from: Wayner on 3 Jan 2010, 07:30 pm

Was it LPGEAR? They have done good for me in the past with Empire belts, tho expensive ($30).

Wayner

I think it was LPGear.

rcag_ils · « **Reply #10 on:** 4 Jan 2010, 07:53 pm »

First, there's no motor adjustment.

Second, the belt that used to be too tight, and make the motor knocking noise, now is too loose and slips off the pulley.

I blame it on the poor quality belts from Ebay.

srb · « **Reply #11 on:** 4 Jan 2010, 08:02 pm »

Since the belt that is too loose is useless now, you could modify it to make a temporary test belt to make sure that you don't have any bearing knock should you locate the right belt.

Cut a small piece out of it and splice it back together with some kind of flexible splicing tape. You may have to do this several times to arrive at the perfect length.

Steve

lcrim · « **Reply #12 on:** 4 Jan 2010, 08:09 pm »

Kevin @ KAB http://www.kabusa.com/frameset.htm?/ carries belts. Much cheaper than LPGear.
You may need to measure the old belt for sizing.

BillWay · « **Reply #13 on:** 4 Jan 2010, 08:45 pm »

The large circuit board under the turntable adjusts the generator that drives the motor. I've found that if the adjustments are out of spec, you can clearly hear the knocking sound from the motor, and when it's adjusted properly the motor will be quiet.

I uploaded the TD125 service manual to my website, fyi here http://billway.us/audio.htm. It's a scan of a gazillionth-generation copy, but the text is readable. Do the adjustments in section #2 (page 4 & 5) but be sure to use the values on the very last page, as the values on pages 4 & 5 are for the Mk I, and the last page has values for the Mk II. There are three adjustments for phase 1, three for phase 2, and three adjustments for speed. To get the phase adjustments right, go over them a few times, as each adjustment affects the others.

rcag_ils · « **Reply #14 on:** 4 Jan 2010, 09:32 pm »

Quote

The large circuit board under the turntable adjusts the generator that drives the motor. I've found that if the adjustments are out of spec, you can clearly hear the knocking sound from the motor, and when it's adjusted properly the motor will be quiet.

Bill,

Thanks for the help, but I don't really see how the motor drive board would cause such mechanical problem.

The speed is dead on for both speeds, and the speed adjuster is right in the middle, while the motor is turning and making the knocking noise.

BillWay · « **Reply #15 on:** 4 Jan 2010, 10:11 pm »

If the two phase adjustments are out of whack, it'll knock, because it won't be getting a good sine wave.

BillWay · « **Reply #16 on:** 4 Jan 2010, 11:07 pm »

Sorry, I was too cryptic.

The 125's motor does not use the 60Hz signal from the wall directly. Instead, the turntable has a small power supply that feeds an oscillator circuit, which in turn feeds an amplifier to provide enough power to drive the motor. The amplifier is a push-pull transformerless design; the "phase 1" and "phase 2" adjustments are there to make sure that both halves (pos & neg) of its output are equal. One benefit of this seemingly over-engineered approach is the inclusion of negative feedback: the output voltage is fed via a linear attenuator back to the base of transistor T4, which is in the input stage of the amplifier, to provide the feedback. Note that the lamp is part of that attenuator, so it has to be working. This feedback loop enables the turntable to correct for small problems, such as my heavy lead mat not being perfectly centered on the platter.

So, the "phase 1" and "phase 2" pots for each of the three speeds must be ± 20% of their specified value. If they are not, the motor may have a lop-sided, or choppy sine wave feeding it, and that can make it go ca-thump ca-thump ca-thump. Get those six pots in spec, and your table should be quiet.

The last three adjustments are to center the red speed-control wheel for each speed. That adjustment can be off without hurting anything, as long as you can hit the speed you want.

And, as long as you are farting around with it, you might as well replace the two 1000mF 25V electrolytic caps, which are C2 and C4. (I think those are the only electrolytics.)

Good luck!

rcag_ils · « **Reply #17 on:** 5 Jan 2010, 12:34 am »

I'll take a look at the manual, but how would misadjusted phases cause mechanical knocking.

p2chiu · « **Reply #18 on:** 12 Jan 2010, 04:49 am »

Hi folks, anybody know the value of a small light bulb ( volt and amp ..etc ) in Thorens 125 speed control circuit board ? Mind one got broken and need to be replaced ? Besides, My Thorens 125 speed is way off, and I cleaned the speed control switch..but it doesn't help...do anybody have tips how to fix this.
Thanks.

rajacat · « **Reply #19 on:** 12 Jan 2010, 05:20 am »

Here's a couple of links that will be of interest to any Thorens TT owners. You'll probably be able to find the bulb value either by exploring the sites or asking a question in the forum.

http://www.theanalogdept.com/thorens_dept_.htm
http://www.vinylengine.com/

-Roy

BTW when I purchased my TD125 it came with a new belt which initially slipped off the pulley quite often. Eventually it quit slipping off and presently it hardly ever slips. Maybe it just needs to be broken in. Perhaps it's the new surface on the belt that has to be worn a little to achieve the proper grip.