Sony TPS-L2 noise when rewind,forward and play

Hi everyone. This is my second post here and i hope i am posting it on the right place. So, I changed all the rubbers on Sony TPS-L2, it works and sound good but since i've never listened a tps-l2 before I can't tell it's good enough. The issue is that there is a low pitch noise when rewind, forward also on play but when play that noise is not that audible but when no tape in it and when i press the play it just gives that noise when i rewind or forward. What might be the causes of this issue? I lubricated it as far as i saw on videos. I would like to hear your thoughts. Thanks in advance

 

I assume the low pitch noise you are talking about is motor hum, but I am not completely sure. Does this noise sound like a buzz ? And does it change with load ?
Like for example when you put your fingers on the reels to slow them down during FF/REW, does it increase in intensity or not ?
And to be clear: is this a mechanical noise or something you hear in the audio ?

Motor hum and it is caused by increased current draw from the motor. This, in turn, is caused by increased load in the mechanism.
You have to check that everything turns freely, especially the small pulley that drives the FF/REW. That pulley's pin usually has old grese on it which makes it very hard to turn.

I do not know what you have lubricated exactly, but you need to go back and re-check, see what turns hard, clean it and re-lubricate. For re-lubrication use oil, not grease.
It is also possible that the motor itself has increased friction and that can also increase the hum above normal levels. In PLAY the hum should be pretty close to inaudible under normal circumstances.

Of course we have to figure out if it is motor hum we are talking about or is it something else first.

 

Thanks for the reply first of all.

It's definitely a hum not buzzing. It tends to increase a little bit when I put my finger on the sprockets while rew/forward. In play mode actually it's close to inaudible as you mentioned. I lubricated the shafts of all gears and just tiny silicon grease to gears touching each other. I used watch oil for shafts. Everything looks turning freely and the playback is actually pretty good. Since i am planning to sell this device I want everything working flawlessly. If it's for myself I wouldn't mind that hum but i want the buyer fully satisfied and use this beautiful device trouble free for 15-20 years. I got all rubber parts from fixyouraudio and I didn't even do any speed calibration. I got it from the first owner, same family kept this all this time with its leather case and mdr-3l2 which more rare than the device itself as you know.

 

It's hard to say without a recording if the hum is wihtin normal limits or not. There are a couple of things that must be taken into account:
- the hum will be higher in FF/REW, that's normal as the load is higher than in PLAY. Given this walkman does not have a muting feature, you will actually hear that hum unlike in other walkmans.
- the MNF-1600B motors do have some variation, some having a bit more hum than others (due to more internal friction), some being a bit more noisy mechanical-wise than others.
However if current draw is within normal limits, there is no concern in regard to the above mentioned.

Given you have lubricated everything, I don't think there's a problem. The motor front bearing should also be lubricated with watch oil if you have not done that already.
But to be sure check the current consumption if you can, it should be 100mA in PLAY, 105mA in FF and 110mA in REW (with no cassette inserted).

 

Can you please show me where exactly i need to put the probes to read the current. Please forgive my dumbness, i am an apprentice and learning everyday. I couldn't figure from the scheme

 

For measuring current, you need to connect the positive lead of the meter to the A/mA socket and connect the meter in series with the walkman.
Here is a an article explaining with pictures: https://www.allaboutcircuits.com/textbook/experiments/chpt-2/ammeter-usage/ (imagine the lamp is the walkman)
Of course pay very careful attention to polarity, as to not power the device with reversed polarity.
The meter doesn't matter if it's reversed, digital meters will display a negative current if that's the case.

 

I mean, to measure the current where do i need to touch the probe tips on the circuit board on the walkman?

 

First of all, you will need to break the circuit in order to measure the current, so the current is deviated through the meter.
It is very important to pay attention in regard to where you plug the positive probe in the meter, as there is a dedicated A/mA port which is designed only for measuring current.
Do not measure a voltage in this configuration, as you will create a short-circuit.

You can simply insert one battery and the second one put half-way in, so it makes contact only with the negative terminal (the spring).
The the multimer probes should complete the circuit: one on the floating positive terminal of the battery, the other on the positive terminal of the walkman.

 

Hi. Sorry for the late reply, i was out for the weekend.

I have to say, the information you shared here is so valuable. I am sure many people will take advantage with these now and in future and will appreciate you. I myself can't thank you enough.

I followed your instructions carefully and saw you were 100% right. The motor draws 122-123 mA when on play, 190-192 mA when FF and 195-196 mA when on Rewind. Higher than it should be according to the numbers given service manual. Now what should we do?

 

Yes indeed it's much higher than it should be. If it was 105-110mA rather than 100mA I would say to leave it alone, but at 122mA it's a concern.
In FF/REW it's even more problematic, as the current is almost double compared to what it should be indicating a serious problem.

Now, you need to see if this increased friction comes from the motor itself, from the mechanism or both.
I would do the following:
1. Remove the main capstan belt and desolder all the motor wires. You can take the motor out completely if it's more convenient.
2. Power on the motor itself without any load at a voltage of about 1.8-2V DC. Check the current draw in this scenario, it should be no more than 20-30mA for a good motor.
If it's more than 30mA, there's internal friction in the motor. In practice it's better if it's closer to 20mA or even lower.
Also note that the current draw of the motor should be more or less the same regardless of voltage. If at 2V it increases compared to 1.8V then it's a problem.

As for the mechanism, the 2 main things I would double check are the 2 idler wheels on which you replaced the rubber on:
- the PLAY one has the pin inserted into plastic and it's very easy to push it too far without realising, causing the idler to turn very hard.
Note that there should be some play (0.1-0.5mm) in that idler.
- the FF/REW one can have the top lock washer bent a bit down or there may be some remaining grease that needs to be cleaned.
If washer is bent, just pry the idler with a rounded tips pair of tweezers until it becomes free to turn. Same thing can be done for the play idler in order to pull that pin out a bit.

Both these idlers can be checked by hand, they should turn completely free without much resistance. The FF/REW one will have some resistance from the gear train, but that should not be much at all.

EDIT: Of course do make sure that the measured currents are without a cassette inserted, as a current of 122mA in play is within normal limits WITH cassette in.

 

Since I don't have the appropriate tip for dc jack, i checked the current with same technique we used before, by just taking out the belt. It reads 54mA. And the FF/REW wheel isn't turning freely but the gear train actually kind of stopping it. Play wheel looks fine. I measured without any cassette inserted.

 

Just taking the belt out is not enough, as there is the servo circuit and the amplifiers which have their own idle currents and I don't know the value of these to substract them.

I have another idea: if you don't have a variable power supply, power just the motor with a fully charged AA 1.5V battery. 1.5V should be enough to get the motor rotating and you should be able to get a ballpark reading.

As for the FF/REW wheel, check the other gears and see where the problem is. Without FF/REW engaged, you should be able to turn that idler with your finger without much resistance.

 

I have a variable power supply. I tried two tips, male jacks i mean, nothing happened. I thought the male jacks aren't appropriate. I checked the capacitor, it reads 280 micro farad, it says 220 in service manual, is that normal? How will i run the motor with a single battery?

 

Let me make myself clearer: you need to measure the current of the motor itself not the current draw of the whole walkman. So forget about that DC in jack, you don't need it.
The current draw of the whole walkman needs to be 100mA in PLAY, while the current draw of the motor needs to be 20-30mA with no load.
The first one we already figured it out it's higher than it should be, now we want to figure out if the increased current is from the mechanism or from the motor itself,
hence why you need to measure the motor out of the circuit (as the circuits themselves have their own current consumption).

Desolder the red and white wires of the motor from the servo PCB and power the motor from the variable power supply at 1.8V (red is positive, white is negative).
See what current draw do you have in this condition (without the belt installed).

Capacitors, when measured at DC will measure more than the rating, while at AC they will measure less than the rating.
So yes, it is normal that a 220μF capacitor measures 280μF when tested with a multimeter/capacitance meter.
In terms of capacitance, keep in mind that bad capacitors will measure less than good ones in terms of capacitance, not more.
So if your 220μF would have measured 50μF for example it would be bad. ESR is one of the parameters that goes higher if cap goes bad.
Also do keep in mind electrolytic capacitors have a tolerance of +/-20% (even when new).

Multimeters always measure in DC, by charging the capacitor at a constant current and measuring the time it takes to charge. This is only a ballpark measurement and will not give very accurate results.
LCR meters, on the other hand, measure in AC and allow you to change the frequency at which the measurement is done and the voltage.
This will give more accurate measurements plus a series of additional parameters like ESR, dissipation factor, etc.

 

So, I guess we are nearing to an happy end It reads 27-28mA. At least we have a good condition motor. So the problem is on the idler tyres and/or gears.

 

Hi. So I cleaned all the gears and wheels and lubricated them once again only with watch oil. Nothing changed and unfortunately another issue occurred this time. After like half way of volume the sound is coming intermittent rapidly and when in maximum it's completely distorted. But before half way, when volume sliders like 4/10 the sound is ok. This happened before when i first installed the rubbers but after i sprayed some contact spray on the sliders it disappeared. Now it came back and resprayed again but didn't go away this time. This is became a frustrating experience already and I don't want to anyone's time but i needed to ask. What am i doing wrong?

 

Perhaps it was an electronic issue based on the linear potentiometer all this time not a mechanical issue?

 

Have you solved the problem by doing something on the potentiometer ? Can't give you an answer since I never seen your device.
The increased current I don't see how it would be caused by the potentiometer.

 

As far i see, every wheel, gear, flywheels are all spinning freely. I checked the motor as I mentioned it draws 27-28mA. Looks fine. Can an electronic component cause increased current? Now i again desoldered the motor wires and removed the screw with a nut which is in the corner of where the sliders are, which is screwed in a white plastic piece in between the boards of the sliders. Because I thought the tension of that screw might be too much and needs to be readjusted. I don't know, i am trying everything i can. Maybe it's two different issues. Distortion when volume up and increased current might be two different issues. I don't know Did i skip oiling some parts? I didn't take apart the piece which is in the middle of plastic pulley and ff/rewind idler tyre, i am guessing it's the auto stop mechanism. I didn't touch it since it have tension pins, springs etc. but it's turning freely as far as i see. If you find it necessary to take it apart and oil it, i will try to that too. As i said potentiometer issue might be totally different issue than increased current. I can't say anything about it