Yaesu Ft-450 only 50 Watts?

Discussion in 'Radio Circuits, Repair & Performance' started by KC3EGP, Jan 29, 2017.

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  1. KC3EGP

    KC3EGP Ham Member QRZ Page

    Hey guys,

    I just got back from winter field day, where I noticed that my radio will only put 50 watts out. I immediately thought that I may have blown one of the finals. The guy who owned the radio before me, had replaced them before, and include the technical manual. We looked through the manual to try to find test points. We completed the PA alignment process with every measurement reading the appropriate amp draw.

    Still I can only get 50 watts out. 20 meters was a bit higher (close to 60 watts) and 10m was significantly lower at 18 watts.

    I also noticed that if I changed the frequency while holing the PTT the power meter would change based on the frequency within the band. (I was using a dummy load)

    The power meter on the radio would sometimes show the correct power, but often it would bounce between 0 and 40 watts. The actual output power would also oscillate between 40 and 50 watts at about the speed of one second.

    I looked at every single component that I could see by taking the covers off and looked at every connection. I did not notice any major defects.

    The receive side is 100% functional.


    Let me know if anyone has insight as to what may be causing this issue. I hesitate to send this old radio away to Yaesu, as the cost may be more than the radio...

    Thanks,
    KC3EGP
    Dan
     
  2. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    The best way to check is to remove the transistors and test them with a tester. I'm fixing one for a customer right now, the symptoms are much the same as you are seeing. One of the finals was blown. Even if only one shows bad it is best to replace both. The Parts and labor are about $150 for finals. It can also be one of the drivers these are much less expensive but the approach is the same using a tester.
     
  3. NN4RH

    NN4RH Premium Subscriber QRZ Page

    How are you measuring the power? The built-in meter in the radio?

    What transmit mode are you using when you make the power measurements?
     
  4. AI3V

    AI3V Ham Member QRZ Page

    Would you be so kind as to describe the tester you use to check rf power transistors?

    Thanks!

    Rege
     
    K8AI likes this.
  5. VE1IC

    VE1IC Ham Member QRZ Page

    check the bandpass filters that are on each band.
     
  6. G4COE

    G4COE Ham Member QRZ Page

    Just a note:

    When we say remove the transistors we DON'T have to remove them literally, simply lifting the base emitter or base collector junctions from the circuit will suffice... or even lifting collector emitter leaving the base intact, this avoids having to remove the transistors completely.

    A simple multimeter will do that has a diode range.... consider a transistor as two diodes in series, the base of the transistor being the junction of the two diodes.

    NOTE:
    Power FET's does not check like a transistor.

    It would be check the PA prior to the filter amd switching board to confirm you get the same fault.



    Dave
     
    Last edited: Jan 30, 2017
  7. KC3EGP

    KC3EGP Ham Member QRZ Page

    I know this is much later, but I broke down and sent the unit to Yeasu expecting to need new finals. They completed a full alignment and everything is working good as new. They only charged me $70 plus shipping. Which was far less than I had feared.
     
    AG5DB likes this.
  8. AE1N

    AE1N Ham Member QRZ Page

    Half the power = half the finals working? Yaesu final replacement costs are very reasonable even if you have to ship all the way to the west coast.
     
  9. KC3EGP

    KC3EGP Ham Member QRZ Page

    The finals had just been replaced. Yaesu determined that they hadn't been properly adjusted for full power output. Both finals were working.
     
    WA9UAA likes this.
  10. 2E0LPL

    2E0LPL Ham Member QRZ Page

    The final or PA recently replaced under warranty on my 450d...under warranty.

    I have used it with the same antenna for 9 months and tune-up under low power.

    After getting it back I used it on TX for maybe 5 mins and the same happened again...low power output on 160/80m...but higher but not full-on 40/20m.

    Is there a common problem on the 450d in this dept.

    Not sure if its going to be repaired again under warranty...I would like to be armed with some info if the is a common problem on the radio.
     

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