K2 - BFO-Test

    Hallo ich bin Thomas ,DK7NU, und baue einen K2 (Nr.8000). Bin im 2. Bauabschnitt. Bis zum VCO-Abgleich hat er alle Tests bestanden. Der folgende BFO-Test schlägt fehl. Ich bekomme kein Signal am Testpunkt 2, weder mit dem internen Frequenzzähler noch mit externen Oszillograf. Der Oszillograf zweigt lediglich schlappe 50Hz an.

    Habe mehrfach die Bauelemente auf Richtigkeit und richtigen Einbau geprüft, L33 auf Durchgang geprüft, OK. sämtliche Lötstellen nachgelötet. Der K2 ist noch ohne Zusatzoptionen und die Bauelemente, welche dafür dann ausgebaut werden müssen, sich noch eingebaut.

    Könnt Ihr mir weiterhelfen oder hat jemand das gleiche Problem?


    Danke im Voraus,

    DK7NU Thomas

    dk7nu@gmx.de

  • DK7NU

    Hat den Titel des Themas von „K2 - BFO-Test,“ zu „K2 - BFO-Test“ geändert.

    Let's do some measurements.
    What is the voltages on each of the 8 pins of U11 NE602?

    VBFO?

    VALC?

    The voltages on the 3 connections of Q24?

    I also think you should ask Don W3PFR, but let's see what this forum can do.


    73,

    Geert Jan PE1HZG

    hello and thank you for your response to my problem.


    Voltages U11


    Measured Manual

    1 1,39V 1,4V

    2 1,39V 1,4V

    3 0,0V 0V

    4 4,8V 5,0V

    5 4,8V 5,0V

    6 5,9V 6,1V

    7 0,0V 5,6V

    8 5,9V 6,1V


    Voltages Q24

    G 0,0V

    S 0,024V

    D 0,024V


    Voltage PIN1 an RP6 VBFO 3,39V

    As you already concluded, the voltage on pin7 of U11 is alarming. Pin 6 and 7 form an oscillator, and according to the NE602 datasheet, pin 6 is the "basis" and pin7 the "emitter" of a NPN transistor. Bias of the transistor is done inside the chip.

    Is this device a regular DIL8 case or a SMD-device-on-a-small-PCB? I wonder about the solder quality on that PCB in the latter case.

    My suggestion is to temporary remove C174 and C173 and see if pin7 remains on 0V. My guess would be a short somewhere. If it does, look if the small PCB has an issue; if not I do wonder about the health of the NE602.

    The NE602 has been out of production for a while and is no longer listed on nxp.com. But there are several places that have the datasheet still:
    https://datasheetspdf.com/pdf-file/500691/Philips/NE602A/1

    Let us know how you proceed,


    Geert Jan

    Zitat von DK7NU

    Pin Measured Manual

    6 5,9V 6,1V

    7 0,0V  5,6V

    Hello Thomas,


    the voltage at pin 7 is way off and implies a short from this pin to ground. As the voltage at pin 6 is OK there must be something else going on at pin 7.


    You could do some basic mesurements with a multimeter/diode tester and the K2 turned OFF:


    [Diode Test] Pin6 - to - Pin8 = typ. 0,82V (BC diode voltage drop)

    [Resistance Test] Pin6 - to - Pin8 = typ. 16,7kOhm (transistor base bias resistor)

    [Diode Test] Pin6 - to - Pin7 = typ. 0,84V (BE diode voltage drop)

    [Resistance Test] Pin7 - to - Pin3 = typ. 23kOhm (emitter resistor)

    vy 72/73, Reinhold.

    Hello OM´s

    I changed U11 and now the signal is available on TP2. However, the frequency is slowly increasing. Since the passive components are OK, only the crystals X3 and X4 or the two varicap diodes remain. But I have already replaced the diodes.
    The crystals are also the right ones, but it is possible that they were damaged when soldering the ground connection. I have put the K2 aside for now and am researching internally for new quartz crystals.


    I wish you a Merry Christmas and a Happy New Year.
    73 DK7NU Thomas

    Hallo Jan, ich bin gerade für mehrere Wochen in einer REHA-Klinik. Ich werde deine Beiträge überprüfen, wenn ich nach Hause komme.

    73 DK7NU Thomas