Yaesu FT101EX... where should I start looking for these 2 problems?

Discussion in '"Boat Anchor" & Classic Equipment' started by KD0YSX, Sep 17, 2021.

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  1. HAMHOCK75

    HAMHOCK75 QRZ Member

    My FT101EE did not come with a microphone. To determine how much output was required from a microphone, I did a complete analysis of the FT101 microphone amplifier. It has again of about 125. The output of the microphone amplifier is on pin 8 of board PB1315. If you speak normally into the microphone, with the microphone gain set to maximum, you should see around 0.5-1 Vrms at pin 8. A scope measurement is best but many ac voltmeters have enough bandwidth to measure it.
     
    N3RYB likes this.
  2. G3YRO

    G3YRO Ham Member QRZ Page

    Yes, many mics are wired differently to the 4 pin plugs - the OP's problem could be that simple !

    With the right kind of microphone, you should only ever need the Mic Gain on number 3 or 4 to fully drive the rig. (unlike the Z series where you always need it flat out!)

    Incidentally, on my FT101 I simply replaced the FET with a bipolar transistor and changed one resistor, and it then worked perfectly with 600 ohm microphones.

    Roger G3YRO
     
  3. KD0YSX

    KD0YSX Ham Member QRZ Page

    Well Boys and Girls,

    I think I'm knackered for now. I've cleaned everything multiple times, tested for voltage here and there and everywhere, reflowed any solder that looked dull or suspect, wiggled wires, reseated and cleaned boards, twiddled various pots and resistors to try to elicit differrent behaviors... nothing. Fine audio, no transmit. Sometimes I need to give the 2 boards on the left a tap to make it come to life, but that's the only thing that seems blatantly out of spec.

    I think I need to gather up a bunch of notes and put them in a ziploc baggy, tape the bag to the case, bolt it all back together and put it away for a few months.

    Very frustrating. But sometimes a break is what's needed.
     
    N3RYB likes this.
  4. G3YRO

    G3YRO Ham Member QRZ Page

    Do you have any modulation when you transmit AM?

    Roger G3YRO
     
  5. KD0YSX

    KD0YSX Ham Member QRZ Page

  6. G3YRO

    G3YRO Ham Member QRZ Page

    Sorry, not been on here for a while . . .

    If you have Modulation on AM, then the Mic Amp is working fine, and Audio is getting to the Mod/Osc Board OK.

    Is the Carrier nulled OK on SSB? (if so, the Balanced Modulator is working.

    The only other likely device failure that would cause no drive on SSB is the FET Q1 on the Mod/Osc Board . . . but if that was the case the ALC meter wouldn't be working. Does the Meter read full scale when you switch to ALC in Transmit mode?

    Roger G3YRO
     
    N3RYB likes this.
  7. KA5IPF

    KA5IPF Ham Member QRZ Page

    Where you been hiding, we were waiting on you.
     
  8. N3RYB

    N3RYB Premium Subscriber QRZ Page

    Okay, so regarding AM modulation, is it just carrier, but is their voice being modulated with it as well(do you hear yourself speaking on another receiver). Asking as there is a pretty well defined flow through the radio and the AM audio path is somewhat different than the SSB path. Would be sort of unusual for the AM path to work, but not the SSB path, IMHO. (Unless there were mode switch issues)
     
  9. N3RYB

    N3RYB Premium Subscriber QRZ Page

    Here is the section of circuit we're looking at:
    [​IMG]

    Your TX audio is going from Pin 8 on the audio board into Pin 9 on the MOD/OSC board(the light blue trace). If you get an AM carrier but no audio. Its probably AF UNIT. If you get audio on AM but no SSB audio, I would look at the mode switch to start with. AM goes through Q2 and SSB goes through the balanced modulator and Q1.
     
    Last edited: Oct 29, 2021
  10. N3RYB

    N3RYB Premium Subscriber QRZ Page

    You know, I wonder if the BFOs aren't running for LSB/USB. If you have another receiver nearby, do you hear anything right at 3181.5 for LSB? Or 3178.5 for USB.
     

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