Technics 1400MK2 speed problem at 33rpm (Flutter/drift)

[Schrei]

Hello!

I posted this question before on previous thread but I think was offtopic.


I Have 2 1400mk2. I changed all electrolic capacitors from both last month for maintenance. One of them works perfect, the other has a speed problem at 33 RPM +1.1 PITCH or slower.

The problem is the same as you can see at the following video (here is with a 1200mk2)

http://www.youtube.com/watch?v=vAWjh3MKLX4

If I pulse several times the 33 RPM switch, the problem seems to be ended(until I brake the platter with my hand or change to 45 RPM and then to 33 ...). If the pitch is equal or over 1.2% the platter spins perfect. At 45 RPM all is working well...

I've a scope and I can view some strange things: for example a 2 HZ pulse (15 V to 0V) at 20 PIN of the AN640 'Drive' IC (this pin is for "Phase condenser"). Some noise at cap C5 of the PSU at 2 hz too. AN640 is OK.

All components (resistors, caps, diodes and transistors) were tested with my multimeter and seems to be OK... The motor system is OK too (turntable were tested with the motor of the other one), Power transistors TR1,4,7 were changed...

I don't know sure if there's relation but I can hear slightly some high frequency noise from the transformer (at 33,45 and stoped, that noise ends if I accelerate or slow the platter down with my hand).

Do you know what could be wrong? It's going me crazy!.


Carlos.

[markyk]

I have a SL-1800 with a more severe fluctuation than the one shown on youtube. Mine has problems at 33rpm, no matter what the pitch setting but is OK at 45 rpm. I did work with the 2 pairs of potentiometers (swapping/replacing them) but that didn't solve the problem. I do notice that adding weight on top of the platter stabilizes the fluctuation. Also, if I set the speed variation to the lowest setting for 45 rpm, it starts to fluctuate. Also, removing the mat, at 45 rpm, it starts to fluctuate. Maybe this clue will lead to a solution - I've noticed several people having this problem (33 rpm bad, 45 rpm OK) with no solution.

[Schrei]

I also replaced transistor drivers, all transistors from "brake release timer" circuit and Motor Controller IC (AN660).. No changes, the problem is still there....In my scope, I can view some strange signals at pins 4 (phase difference output) and 7 (amplifier output) from AN660 IC only shown when there's fluctuation.

ARGH!

Carlos.

[markyk]

Have you tried swapping the platters between the turntables? There's a magnet (and other parts) in the platter that's a crucial part of the motor in the platter.

[Schrei]

Hi, markyk!.

Yes, I swapped platters, the motor system (motor and spindle) and some ICs...Same fluctuation

[markyk]

Schrei, it sounds like just about the only thing left is the power supply.

[Schrei]

About the power supply: I swapped rectifiers, I've replaced the 3 Power-transistors and I've tested all components with my multimeter, but the transformer but I think it's ok...

[markyk]

I opened up the motor on my SL-1800 today to clean it up. I found out that it had been over-lubricated (not by me). I've ordered the lubricating oil and I'll see how it works out. Without lubrication, it's pretty unstable. I mention this because you might want to look for any physical anomalies that may cause an issue (since you've tried so many other things). As I mentioned earlier, for me, removing the mat causes fluctuation at 45 rpm, adding a little weight stabilizes the fluctuation at 33 rpm. It also seems to me that electronic-based issues would cause more problems than just at +1.1 pitch or lower.

[Schrei]

Did you try to clean your speed selector switch with CRC?.

About lubrication and friction: after all electrolytic caps were replaced, I polished the spindle bearing base to a mirror finish (1 micron) and I added an hard steel polished to mirror finish thrust plate lubricated with molybdenum based grease on both turntables, I did this with my technics sp-15 too and it works perfect, much better than before (it shares the 4 logic ICs and other circuits with 1300/1400/1500MK2 line and with SP10MK2A and SP10MK3). Only one turntable fails so I don't think that the problem can be caused by an improved bearing system with less friction, but who knows... this issue seems to be a X-file!.

[Schrei]

After taking a deep, deep look at the SP10mk2A service manual (at the schematic diagram) I found the problem. The problem is located at FG (frequency generator) circuit, one transistor was faulty (verified before with my scope). The diode testing tool of my multimeter wasn't useful with this.

I hope this helps somebody!

[Schrei]

The problem isn't generated (only) by this transistor, it's generated by age!...all resistors have changed (slightly) their tolerance... and FG circuit seems to be very sensitive with this... a simple high value resistor in parallel with the resistor (R222) tied to the first transistor solved the issue completely. In fact it seems to work better than the other turntable (I'm tired and I don't want to change all resistors).

This is the end, my only friend...

[markyk]

I'm glad you solved your problem - you certainly deserve being rewarded for your perseverance. As for me, my problem remains but after cleaning out the spindle and re-lubricating, the problem now looks like the youtube problem (before my wobble was worse and inconsistent). I think your experience will certainly help other people and I'll probably go down that route. Transistors and resistors can be replaced - the motor components and the IC(s), not so much.

[Schrei]

I think your motor should be OK. For your model you can try the following: download the service manual here: http://www.vinylengine.com/ve_downloads ... ervice.pdf

-Check speed selector switch (with your ohm-meter).
-Check Power Switch (disconnect your turntable from wall plug before!!)
-Replace all electrolytic capacitors (due to its age, all caps must be replaced).
-Check voltages from your power supply (at E,B,C terminals of the 2 transistors of the Power Supply).

[markyk]

Schrei, I got the service manual for SL-1700 (SL-1800 is the manual version) before opening it up for the first time. The speed selector switch was cleaned and checks out on the meter. I'll check the power switch. I replaced the 2 transistors that the SL-1800 has and the 1w resistors (3) and the wobble is still there, but is improved. I'll go the capacitor route next. Thanks for the advice.