Icom 756 Pro2 stops receiving when warmed up

Discussion in 'Radio Circuits, Repair & Performance' started by WA4MNT, Apr 28, 2019.

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  1. KL7SG

    KL7SG XML Subscriber QRZ Page

    Yes, it is a switch. I could only guess on a replacement. Give me a minute to see what 2N3904 is.
     
  2. KL7SG

    KL7SG XML Subscriber QRZ Page

    It looks like it should be OK to try it.
     
  3. WA4MNT

    WA4MNT Ham Member QRZ Page

    My inexpensive says the 2sc4213 is bad
     
  4. KL7SG

    KL7SG XML Subscriber QRZ Page

    Also remember, the left side of R154 voltage controls Q25. The Q13 side of R153 voltage checks the status of the Q13 emitter (on/off state). It takes at least two conditions to turn on the relay. Maybe more because there are multiple connections to the emitter of Q13.
     
  5. KL7SG

    KL7SG XML Subscriber QRZ Page

    Does the radio operate normally with Q25 removed?
     
  6. KL7SG

    KL7SG XML Subscriber QRZ Page

    Oops receive normally with Q25 removed
     
  7. WA4MNT

    WA4MNT Ham Member QRZ Page

    Well it doesn't go to mute when Q12 heats up. But the voltages are quite different. Q25-B .01V, Q25-C is 3.5V.

    I guess I better order the right transistor. The squelch control squelches at either end of the control, but good for the center third of it's range.
     
  8. WA4MNT

    WA4MNT Ham Member QRZ Page

    I didn't try it without Q25
     
  9. KL7SG

    KL7SG XML Subscriber QRZ Page

    Different voltage are to be expected. This shows that the control signal shutting down the receiver, via Q13, is coming from Q25 not the control signal for Q25 or other signals at the emitter of Q13.
     
  10. KL7SG

    KL7SG XML Subscriber QRZ Page

    Did you remove Q25 to test it?
     

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