Problems with Saba Freiburg 7's automatic tuning

      Problems with Saba Freiburg 7's automatic tuning

      Hi, and greetings from Finland

      Ufortunately I don't speak any German but I hope I get some help in English language.

      I have a tube radio, Saba Freiburg 7. Everything worked fine, but yesterday the automatic tuning stopped working. The automatic's fine tuning seems to be working, since the tuner automatically tries to find the best reception (the tuning knob vibrates).

      The poblems is that the search doesn't work. The motor runs search run or rapid run to both directions when I push the autotuning knob but the electrical magnet coil - that keeps the autotuning knob on the search position - doesn't work. The coil doesn't form any magnetic field and thus the auto-tuning knob disengages immediately when I take my finger off it.

      I have tried to find broken capacitors or resistors but haven't found any yet. I've also tried many EABC80 tubes with no luck. There's absolutely no magnetic field in the electrical magnet coil at all. I hope the electrical magnet coil is not broken.

      There's the scheme of the automatic tuner as an attachment. I've marked to the attachment the capacitors and resistors I've already checked. The electromagnetic coil gets about 280 V DC all the time whether the auto tuning is switched on or off. Should that be like that?

      I also found an old post from another site (radiomuseum) where someone had the same problem with the same radio model. He told that the problem was very easy to fix because it was caused by some EABC80 related resistors thad had a base contact or short circuit. Unfortunately he didn't tell what resistors he was referring to. I can't find any short circuit from the radio as I don't know where to look for one.

      Thank you for your help in advance!

      -Ville
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      • Automaatti.jpg

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      Hello,
      did you check the diode under end switches? If you press the button, then part of engine voltage is rectified by it which in turn overcomes negative bias of EABC80, the tube starts conducting current and thus the magnet holds.
      Did also replace capacitor between engine and that diode? Or just checked it?

      Regards
      Piotr

      Hallo Ville,

      die Magnetspule am Steuerhebel kannst du ganz einfach überprüfen, in dem du die Spannung direkt an der Anode der EABC80 (pin9) mißt. Sie sollte ca. 280V betragen.

      Sollte diese Messung positiv verlaufen, kann der rot gekennzeichnete 1M Widerstand defekt sein. An dem Punkt "!" muß bei Suchlauf eine positive Spannung >10V vorhanden sein.

      Wenn dies nicht der Fall ist und die Kondensatoren 0,05µ der 0,025µ und der 100k Widerstand ok. sind, könnte einer der Endabschalter dauerhaft geschlossen sein.

      Hallo Ville,

      the solenoid on the control lever, you can easily check to see where you measure the voltage directly at the anode of EABC80 (pin9). They should be about 280V.

      If this measurement is positive, the 1M marked red can be resistor defective. At the point "!" must be present when scanning a positive voltage> 10V.

      If this is not the case and the capacitors of 0,025μ 0,05μ and the 100k resistor ok. are, one of the limit switch may be permanently closed.
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      Freundliche Grüsse, sagnix

      Hi,

      Thanks for your answers! It seems I've come closer to the solution. When I was measuring the voltage at the soldering point of the 1 Mohm resistor, the 0,25 uF capacitor and the rectifier diode (marked with an exclamation mark on the scema), the automatic search started to work again. Maybe there's a bad soldering point somewhere. I will check the solderings right away.

      Many thanks to your help!