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Pioneer SX-737 No FM

Discussion in 'Electronic Repair' started by Gary L. Woodruff, Apr 7, 2009.

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  1. Howdy all, I have a vintage Pioneer receiver. It will pick up AM
    stations but is dead on FM. I do not get any deflection on the tuning
    meters and no static. I do have a print. I do have b+ into the board and
    have good voltages at the HA1156.
    I do not see anything at the HA1137, with the exception of 13.8v at pin 11
    (should be 5.6v). There is only a coil in series with a cap to gnd
    between b+ and this pin. I do not have a way to measure inductance
    on the coil but have measured the cap .047 microfarads is spec and
    I get .055. I am tempted to try to replace the IC (HA1137) but am
    concerned about the amount of voltage I see on pin 11 of the IC.
    Any and all advice is GREATLY appreciated.

    Thanks, Gary
  2. David Farber

    David Farber Guest

    That 5.6 voltage should be for pin 10, not pin 11. Pin 11 goes to the B+
    supply and the 13.8 v is correct.

    Good luck.
  3. Dave, thanks for pointing that out. the 13.8 is the only voltage I see
    on the HA1137. I do not see the input signal of 1.9v on pins 1,2,3 of
    the chip. I do see the 12.6 v at F2 but nothing after. I will try to
    replace this fuse? F2 and the HA1137. Does this make sense?

    Thanks, Gary
  4. David Farber

    David Farber Guest

    F1 and F2 fuse one of the pairs of wires coming off of the secondary of the
    power transformer. In the FM section, there is another component which also
    labeled F2 which appears to be some sort of I.F. filter. You need to tell me
    if by F2 you mean the fuse or if you mean the filter. You cannot have the
    13.8 volts at pin 10 if the fuse is blown. Do you have the correct voltages
    on Q4?

    Good luck.
  5. Howdy, thanks Dave. Yes I do see 13.7V at the collector, 1.4v Emitter
    ..21v at the base. I do not see anything on the output of the F2 filter
    (I missed the F2 listing in the tuner part list, and found it listed as
    a fuse, thanks again).

    Thanks, Gary
  6. David Farber

    David Farber Guest

    I believe we've found the problem. I am not in the office at the moment
    where my schematic is, but if Q4 is reverse biased, that's going to be a
    dead end for the signal right there.
  7. Dave, thanks again. What do you think is causing q4 to be reversed biased?

  8. David Farber

    David Farber Guest

    Sorry I couldn't get back to you sooner. Remove Q4 from the circuit and test
    it with your multimeter. Also, check the voltage at the base of Q4 were it
    still in the circuit.
  9. Dave, I removed Q4 from the circuit and it is OK. I checked the voltage
    at the base with Q4 out of circuit and get 2.1 V. I resoldered Q4 and
    checked the base again and still get 2.1 at the base. (I may have
    misread my previous reading of .21v) I do see 13.7v on the Q4 side of
    the f2 IF filter but 0v at pin 1 of HA1137. i am thinking I need to
    replace this F2 if filter?

    Thanks, Gary
  10. David Farber

    David Farber Guest

    Well the difference from .21 and 2.1 is quite a difference. That means the
    transistor is operating correctly. I would replace the HA1137 and see if the
    voltages come back up. It's not very likely any of those filters are bad.
    You could remove F2 and see if the voltage comes back up just to see what
    happens though.

    Good luck.
  11. To all who helped, thank you. I replaced the HA1137 and all is working.
    Thanks!!, Gary
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