Repair Notes for Bendix Model 3TBD AM Radio


Posted on Feb 5, 2014

Externally, the chassis looks identical to the 22BD. Exception: the 22BD has the jack for the speaker connection - two female sockets - on the right (antenna) side of the chassis; the 3BTD has a 3` harness (Black and Green wires) exiting the left side (same side as the power leads) and is a combined male/female connector.


Repair Notes for Bendix Model 3TBD AM Radio
Click here to download the full size of the above Circuit.

Refer to the pics I have of the earlier 22BT model. A good location to find the AM signal, is the connection shown below (if the RF/Converter/IF stages are OK). You`ll only get a waveform if you`ve tuned in a station, so watch the `scope while tuning. . . I pulled the first two transistors in the amplifier stage (Q4 & Q5) and they looked good and checked OK, checked a few resistor values, all looked OK, soldered everything `em back in and lo! All of a sudden, it plays. I *hate* that. "Early solid state car radios used all germanium transistors. The most common failures were the RF amp, Local oscillator, and the converter (Mixer) transistors. The easiest way to find the bad transistor is to check the collector votages. If you find one that`s near zero, the transistor is open. I used to test, find the bad part and repair the radio in less time than the service clerk took to write up the work order, and all I used was a meter, signal tracer, and an old signal generator. Over 95% of the failures were open transistors, and the replacement parts weren`t critical Something rated for RF in the low ECG numbers worked very well. " Well, open transistors are not terribly common on the monitors I`ve repaired (different tech, different era, no germanium stuff), so I am grateful for this advice from someone who`s been there. After two days` running on the bench, the radio is still running fine, but I think I`ll just replace all the...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    LED Dice II
    Automatic-shutoff
    Count Down Timer Circuit
    Car Boot Light Warning
    amplifier circuit
    RCEN fuse bit blower for the AT90S1200 8Bit RISC CPU
    Using C-MOS light emitting diode drive circuit NAND gate pulse
    INA217 professional miniature microphone microphone circuit diagram of a typical preamp



    Top