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-   -   Need replacement for IC : SFC 2709 E (http://www.diyaudio.com/forums/parts/65320-need-replacement-ic-sfc-2709-e.html)

Illusus 3rd October 2005 04:48 AM

Need replacement for IC : SFC 2709 E
 
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 15th October 2006 05:21 PM

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 16th October 2006 02:05 AM

Any picture of it???

anatech 16th October 2006 02:27 AM

2 Attachment(s)
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! :D

totor 16th October 2006 09:54 AM

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 16th October 2006 09:54 AM

2 Attachment(s)
here is a picture of IC on the board

anatech 16th October 2006 11:49 AM

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 16th October 2006 12:28 PM

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 16th October 2006 12:37 PM

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.
Quote:

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.
Quote:

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 16th October 2006 03:56 PM

Quote:

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 ?

Quote:

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 ;-)


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