Need replacement for IC : SFC 2709 E

[Illusus]

Need replacement for SFC 2709 E, it's for an oscillator in a Thorens TD125 MKII. Anyone have a substitute or a source of a replacement? Thanks.

[totor]

Hello,

I am new user of this forum and obviously I need your help.

I have a problem with an IC of my thorens turntable, a 125 mkII. I am searching for two SFC 2709 E and I can't find them.

Could you please tell me where to buy some ? Or is there an equivalent ? I am not an electronic specialist.

Thank you very much for your help.

[Leolabs]

Any picture of it???

[anatech]

Hi Guys,
I've never had to replace one of these - ever. Not unless the table was "struck by technician", or worse.

Here is a picture Leolabs ......

It may be a uA709 or something like that.

So why do you think these need replacement?

-Chris

Edit: They are LM709 in a 14 pin dip. What a guess!

[totor]

Hello and thank you for replies.

I have a problem with my 125 mkII. I don't manage to obtain the good voltage on motor power. Then, the motor don't turn but I feel vibrations and I can't turn it by hand.

I have already changed the two big capacitors and four transistors too.
I have changed IC by LM709 and try LM741 too. I have power to motor but it still doesn't work. I have too much power and I can't adjust to good voltage. I have 17V and 12V instead of 8V and 8V for 45rpm for example.

Maybe a wrong IC reference ?

I have no idea of what to do now, so help is welcome. If someone have advice ...

Thanks

[totor]

here is a picture of IC on the board

[anatech]

Hi totor,
My bet is that the lamp is open.

Have you checked the wave forms with an oscilloscope? This is a sine wave generator (wein bridge) and nothing more. If you have a square wave, I'd guess the gain control lamp is open. There are two ways to kill the lamp. Run the voltage too high for a long while, or drop the table and the filament breaks.

The two drives are 90° out of phase. At this point, I would re-install the original parts unless they are damaged. The chips are LM709's, but any 709 make will work fine.

I hope the motor is okay after all of this.

-Chris

[totor]

Hello anatech,

I haven't test sine waves because I have no oscilloscope.

Can I ask you what is the lamp you are talking about ? Is it the bulb that make light when there is too much voltage difference between sine wave ? this bulb is ok and still make light on the board.

I hope I am clear enough, as I said I am not a specialist.

[anatech]

Hi totor,
I hope you are then using an AC voltmeter or a Fluke to measure the amplitudes. DVMs (most) have very poor high frequency response. There is no way to set this table up with cheap meters.

Is it the bulb that make light when there is too much voltage difference between sine wave ?

Either your controls are badly misadjusted or the lamp is the wrong one.

this bulb is ok and still make light on the board.

That lamp should never be lit. At the most, a dull red glow, very faint. But, yes, the lamp appears to be okay. It's a very low current bulb.

How did you get to this point (why did you start working on the turntable)?

At this point I would center all the pots and run through the adjustment procedure again. Make sure you are using a meter that is flat to 1 KHz, not one that says it's bandwidth goes to 1 KHz (-3dB). Your lamp should never glow. The voltage is far too high in that case.

-Chris

[totor]

I hope you are then using an AC voltmeter or a Fluke to measure the amplitudes. DVMs (most) have very poor high frequency response. There is no way to set this table up with cheap meters.

Yes I am using a little Voltmeter with AC position.

I have put LM709 14 pin on the board and I obtain :

- between ge and bt : 12 V
- between ge and rt : 9,4 V

I can't adjust voltage between ge and bt, turning the pot is useless.
I can adjust between ge and rt, but the max voltage I can obtain is 9,4 V.

Then I think the problem is I can't adjust the first one but I don't know where it can come from ... any idea ?

How did you get to this point (why did you start working on the turntable)?

I have started this way because the motor has never turned. I just have bought this turntable and I hope to make it work. I already have a TD166 but this 125 seems really better ... not for the moment ;-)