Technics FM Tuner switches from stereo to mono to beat of music!

[ssi]

Happy with it! Not ground breaking sound but good for the garage and my electronics tinkering space. Using it with a Pure Highway for DAB (BBC 6 Music) which has a built in FM transmitter for use in cars and works great for the garage. My car has DAB so no longer use it. The Wharfedale Diamond III's are not too bad and fit on a small shelf. Using it with my JVC AX220 (35wpc - diamonds hard to drive) but may try it with a Technics SU800 (50 wpc) which I have in the loft. All this kit (not DAB!) has lasted this long (30 years) so should survive a UK garage (dry).

 

[davidsrsb]

T101/2 off tune causes the FM detector and mute circuits to do just what the OP reports. Mooly should really say never touch the front end. Adjusting the FM detector can be done with a simple multimeter.

 

[Mooly]

Mooly should really say never touch the front end.

I thought I did 🙂

I would advise caution on altering any of the tuned circuits, once you do you will never be able to bring them back again without correct test equipment.

 

[davidsrsb]

The FM detector coil is the only exception, and that one only the primary coil should be touched. Adjusting the secondary coil requires a test generator and distortion analyser

 

[DF96]

The term 'front end' means different things to different people. Some (including me) use it to mean the VHF part of the circuit. Others may use to mean everything up to and including the discriminator.

 

[Osvaldo de Banfield]

Front end usually refers to the part from aerial to first IF transformer coupling, like in old TV sets.

 

[ssi]

Did this and fixed it - finally got round to it!

None of these, it's T101 for centre tuning. Use TP101 and TP102 for checking the center alignment. Tune to strong station, use a digital voltmeter. The polarity does not matter when measuring TP101 and TP102, all you care about is adjust T101 until you get as close as possible to zero volts between the 2 test points.

Check the AC ripple across C708 100uF/35V, it should only be about 10mV or less. It is possible that C713 100uF/35 that is part of the voltage doubler is dried up. C713 can be increased safely to 470uF/35. This capacitor has a hard life due to the amount of AC voltage across it. Increasing the capacitance will make it last longer.

Replace C705, C706 and C707 too.

Don't even think of installing boutique capacitors into this tuner, it is not worth it.

 

[ssi]

Thanks ej25awd

 

[Mark Tillotson]

Front end usually refers to the part from aerial to first IF transformer coupling, like in old TV sets.

Front end is upto the first mixer usually. The front end is the only part of a receiver that has to be tunable.

 

[ssi]

Since changing the power supply related caps the display seems a lot sharper and brighter.