QX-949 Power supply issue

Discussion in 'Pioneer Audio' started by KeithD, May 6, 2018.

  1. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    Any chance this is a cap issue? I see C36 is between pin 17 on the tuner board (connected to pin 6 on power supply) and ground. Pin 17 is also connected to R40, which leads to C52 - ground, so yeah, lifting R40 would isolate Q8.
     

     

    Please register to disable this ad.

  2. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,802
    Location:
    uk.. the middle bit
    c36 is a possibility .
     
  3. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    This will be more difficult than I anticipated. I can loosen the tuner board by removing the fastening screws, but there is no way to lift the board far enough to get access to the foil side without disconnecting at least some of the wires from their respective pins. The best plan may be to disconnect wires, and recap the entire board hoping that will solve the problem. I don't see how I can realistically disconnect and reconnect wires multiple times to do testing.

    Is there any other way to test what might be bad on this board?

    John, did you recap your tuner board?
     
  4. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,802
    Location:
    uk.. the middle bit
    best way is take voltage readings at the correct spots all tuner pins voltages to start with .... right across r40 might tell us something .
    setting to fm or am might change things .
     
  5. Unjoy

    Unjoy New Member

    Messages:
    49
    Location:
    Apeldoorn, Netherlands
    Do you have access to a (regulated) power supply that can feed the tuner board separately? And measure current? Or more brutal: a power supply that is able to deliver some decent current. You should be able to feel (or see...) if something gets hot on the tuner board (one of the IC's or maybe a capacitor).

    I still think it can be something else, since I do not see how some kind of short (either capacitor or IC) on pin 6 can affect the 30V supply: schematic mentions the 30V supply delivering 150mA, the current flowing to the 13.5V supply through R3 supply can never be more than 30V/R3= 9mA. It should not affect the 30V.
     
  6. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,802
    Location:
    uk.. the middle bit
    yes it is rather odd in theory it shouldn't be so . but it is appearing so .
    just for fun measure voltage at pin 6 again no wire attached . plus get voltage at disconnected wire .
     

     

    Please register to disable this ad.

  7. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    Here are voltages: Pin 6 with no wires attached: 13.2V. Wire to tuner board: -0.018mV. Voltage difference across R40: 0.84V.

    I could borrow a regulated power supply from work and try to measure amps. Couldn't I just measure that with my DMM connected between pin 6 and the wire to the tuner?
     
  8. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    Just tried it. Connected one lead of DMM to pin 6, other lead to tuner wire. Measurement was 72mA!
     
  9. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,802
    Location:
    uk.. the middle bit
    see if current changes in fm or am .
    also try every other switch .
     
  10. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    No, initial reading I reported was with selector on AUX. When I flipped to FM reading went to 79mA. Stayed the same on FM mono or AM.
     
  11. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    R40 is showing 0.84V
     

     

    Please register to disable this ad.

  12. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,802
    Location:
    uk.. the middle bit
    see if anything on tuner board is hotting up
    r40 drop is lower than expected . dont see a problem there .
     
  13. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    Nothing obvious getting warm after about 10 minutes. Checked the ICs, e-caps, and as many resistors as I could get my finger on. Voltage on pin 6 was steady at 12.7V, and pin 8 of power supply at 27V. Unit was in protection the whole time. Once I disconnect pin 6, pin 8 goes to 29.8V and the unit comes out of protection.
     
  14. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,802
    Location:
    uk.. the middle bit
    ah .. pin 6 likely a red herring ....that was suspected . .
    so we need 3 more volts to pin pin 8 .
    did you clean fuse holders yet ?
    also check negative supply voltages
     
  15. Unjoy

    Unjoy New Member

    Messages:
    49
    Location:
    Apeldoorn, Netherlands
    I would suspect there is something wrong with Q4. Are you sure that Q1 and Q4 are properly isolated from the heatsink? What are voltages on the legs of Q4?
     
  16. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    Just a reminder from post #1 how this started. I had recapped the power supply, all seemed normal. I was letting the unit warm up for about 20 minutes. When I came back to it, it was in protection. To me, that points to something going bad during the warm up time. Changing all the transistors improved things a bit when I replaced Q4 (see post #22), but nothing else.

    Here are Q4 readings with pin 6 connected, pin 6 disconnected, and readings from a good power supply on a different 949:

    E, C, B
    Pin 6 connected: 11.1, 34.2, 11.3
    Pin 6 disconnected: 13.3, 48.7, 13.8
    Pin 6 good PS: 12.9, 32.8, 13.6

    Did put a piece of paper behind Q4 to make sure it was isolated from heat sink. No change in reading.

    Cleaned fuse holders and replaced all fuses, as they seemed a bit oxidized (see post #3).

    Here are all PS voltages with pin 6 connected (and expected values from good PS):

    VAC
    1: 46.2 (46.0)
    2: 46.2 (46.0)
    3: 7.2 (7.3)
    4: 37.9 (37.7)
    5: 37.9 (37.3)

    VDC
    6: ~11 (13.0)
    7: 0 (0)
    8: ~27 (31.0)
    9: 0 (0)
    10: 0 (0)
    11: 9.3 (8.7)
    12: 9.3 (8.7)
    13: 0 (0)
    14: -44.3 (-44.2)
    15: 0 (0)
    16: -38.4 (0) difference here is because pin 16 is connected to a filter cap on one unit and ground on the other unit. The first configuration follows the service manual, the second one follows schematics. Both appeared original factory wiring.
    17: -13.3 (-12.7)

    With pin 6 disconnected, I am still getting noise on the rear channels, and I can only get the DC offset on pins 5 to about 0.3V (should be at zero) on both rear channels.

    The voltages supplied to the board seem good, so something is going wrong getting to pins 6 and 8. Interesting that pins 11, 12, and 17 are all 0.6V high. Could this be an issue with the power supplied to the board? As I mentioned in post #18, there is fluctuation in the B2 voltage coming PS board B, which is part of the power to the rear channels, and I wondered if that could be causing the rear channel noise?
     

     

    Please register to disable this ad.

  17. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,802
    Location:
    uk.. the middle bit
    did you try with pin 6 and 8 disconnected yet ? and also measure voltage at disconnected wires .
     
  18. KeithD

    KeithD AK Subscriber Subscriber

    Messages:
    538
    Location:
    La Crosse, WI
    With pin 6 disconnected, pin 8 is 30V as it should be (post #37).

    See post #27 for voltage on pin 8 with wires on 8 disconnected.

    Post #47 has values for pin 6 and wire voltage.

    Did not measure voltages on wires connected to pin 8 when they were disconnected (there are 3), and at this point I have soldered them back on. Don't see that the problem is there anyway, since voltage on pin 8 is normal when pin 6 is disconnected. It's pin 6 connection that is causing the problem, right?
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,802
    Location:
    uk.. the middle bit
    yes it does appear that way .
     
  20. Unjoy

    Unjoy New Member

    Messages:
    49
    Location:
    Apeldoorn, Netherlands
    I am still thinking pin 6 as well. I know you replaced Q4, and that things got a little better. But E, B, Pin 6 connected: 11.1V, 11.3V is not ok. I would expect to see 0.6-0.7V difference as you see on the good supply. Do you have another KSC2073, or try the SD313 again for Q4? And just to be sure grounding is ok, can you measure resistance between pin 7 and metal chassis, and pin 9 to metal chassis? This is really strange...
     

Share This Page