1980 FM tuner dead

Discussion in 'Pioneer Audio' started by jtee1340, Feb 18, 2017.

  1. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    20,984
    Location:
    Bensenville,Illinois
    Have you checked the transistors you replaced?

    No sensor gain switch, so we can't fool with that, could the humidity at where it is, be lower (cold winter) than usual?

    I'm trying to remember if grounding the tuning knob defeats the touch function. Worth a try as it's easy...
     

     

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  2. txturbo

    txturbo AK Subscriber Subscriber

    Messages:
    868
    Location:
    Austin, TX
    Hi Mark,

    I have not checked the transistors yet, I will have some time to dig into it tomorrow.

    I think that following the first step of the alignment procedure, connecting terminal 25 to 12 with a 100K resistor disables the APC. If I remember I had to pull Q27 to disable the touch? I will try and isolate the part that's a problem.

    I wonder if jtee1340 ever got his working...
     
  3. jtee1340

    jtee1340 AK Subscriber Subscriber

    Messages:
    512
    Location:
    Tampa Florida
    The owner of the 1980 decided to send the unit out to a guy in Texas. Bill at Circle Stereo. It's been there a while, and I don't know the status of the repair.
    That tuner section is pretty complicated and I didn't feel comfortable tearing into it more than I had.
    I will keep you all abreast of the repair as I hear the outcome.
    Hope you get yours up and going txturbo. Thanks to all that offered great advise. "But a man's gotta know his limits" as I think Clint Eastwood said.:smoke:
    J.T.
     
  4. txturbo

    txturbo AK Subscriber Subscriber

    Messages:
    868
    Location:
    Austin, TX
    I checked the transistors and they seem to be ok.

    The more I look at this tuner the more I can see it has been worked on quite a bit. Many of the wire wraps have been soldered. Maybe that was simply done to make sure that the wires were making contact.

    I attempted to repeat the procedure that seemed to work last year but that did not produce the same result. It seems that the tuning meter pin on the PA3001 always has an output equal to B+ (12V). With the power off I measured the resistance between B+ and Pin 7 of the PA3001tuning meter output. On the bad tuner I get .7K Ohms. On a working tuner I get 13K Ohms. That's all I could get done for today.

    Tomorrow I will remove PA3001 and measure the pins out of circuit. I suspect that the IC is no good.
     
  5. txturbo

    txturbo AK Subscriber Subscriber

    Messages:
    868
    Location:
    Austin, TX
    I have been working on the tuner for a few days on and off. So far I have made little progress.

    The main crux is that the tuning meter is slammed to the left and the mute signal is activated from the 3001A.

    I have checked every part of the circuit around the PA3001A multiple times. I have gone so far as to swap the PA3001A and detector coil assembly with a working receiver. No joy. Every resistor, cap and coil has been checked.

    Basically pin 7 on the PA3001A is driven to 12V. In this condition the tuner is hardly working, no fine tune, quartz lock or stereo.

    If I lift R18, disabling the mute signal, the fine tune, quartz lock and stereo sections work. In this condition I can adjust the coil for minimum distortion.

    I am missing something obvious.
     
  6. rcs16

    rcs16 Super Member

    Messages:
    3,506
    Location:
    Baldwin, Ontario, Canada
    Yeah that is weird,
    So I assume that, pin 7 on the PA3001A(AFC) then goes to its proper voltage ~5.7V
    This is a big clue, follow that mute signal, "n" as shown in the big schem, what ever it connects to is throwing the whole mess off, check the DC at all the points the mute goes too, see if anything is off.
    "n" goes into apc pcb pin 3, a schmitt trigger ckt(q1,2) and comes out on pin 5 as a switched DCV "r". check bias voltages as shown on the sch, you can check the schmitt trigger switching thresholds with an external DCV.
    I have shitty schematics, hard to follow "r' around.

    Good luck
    Rick
     

     

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  7. txturbo

    txturbo AK Subscriber Subscriber

    Messages:
    868
    Location:
    Austin, TX
    Problem solved! It's the reed relay in the APC board.


    The relay was not failed open or short. It had some resistance while open. Because it's in parallel with the meter it was not easy to diagnose. If you check between pins 30 and 31 of the tuner board side by side with a working receiver the only clue was that the ohm reading takes a few seconds to stabilize on the bad unit, like a charging cap.


    It all makes sense now. Last year I thought the transistors that drive the relay were bad. I grounded the collector of Q27 on the tuner board, forcing the relay on the APC board to close. I checked the rest of the circuit and the signals that drive the relay circuit seemed ok so I replaced the transistor and the circuit was operational again. What I had actually done is exercise the relay, in doing so broke the high resistance while open condition temporarily. This is why when I checked the transistors that were removed on the bench they were OK.


    Why does the meter slam to the left in this condition? The relay serves two functions, one is to shunt the meter once quartz lock is enabled. The other is to complete the PLL circuit once the conditions of fine tune, no mute and no hand on the knob have been satisfied. If the relay contacts for the meter have resistance when open the quadrature tank circuit will be un balanced causing the PA3001 to believe that the tank circuit is greater than 70 KHz away from the tuned frequency, causing the mute function to stay high. Pin 7 is also trying to drive current, causing the pin to hit VCC making the meter slam.


    To anyone in the future that has a problem with the meter being slammed to one side (especially the left) remove the blue wire on pin 5 under the APC board. This will remove the relay from being paralleled with the meter. In this condition the touch lock sensor, fine tune, stereo and quartz lock led's should work.

    I am working on a small daughter card to hold a modern reed relay to replace the original. You could always dead bug one in place.

    I would recommend that in the future whenever a service or full recap of a 1980 is completed that this part be replaced. When you look at what it is doing for both sets of contacts in the circuit it could cause a performance problem that may be difficult to detect. The relay may somehow become damaged when the power supply fails as well. It is very cheap insurance.


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  8. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    20,984
    Location:
    Bensenville,Illinois
    That is impressive troubleshooting. :thumbsup:
     
  9. txturbo

    txturbo AK Subscriber Subscriber

    Messages:
    868
    Location:
    Austin, TX
    Thanks Mark.. :)

    I installed the replacement reed relay, works perfectly. I used a Hamlin HE722A1200 on a single sided perf board.


    I am sure that there are other reed relays that would work. Just be sure to get one without the suppression diode.




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  10. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,555
    Location:
    Las Vegas Nevada
    Well done.
    The suggestion will be followed.
    Nice install package.
     

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