7070 Relay not clicking (again)

Discussion in 'Exclusively Sansui' started by G Heiman, Feb 28, 2018.

  1. G Heiman

    G Heiman AK Subscriber Subscriber

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    Location:
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    I have a 7070 receiver that did the classic worked when turned off, won't turn back on. I've read through several threads about similar problems and have replaced all of the fuseable resistors on board F-2624. Still no relay click on turn on. I can set the bias on both channels but cannot adjust the DC output voltage on either channel which is 4.3 volts. If I pull board f-2624 and turn the unit on, no click. If I pull both F-2624 and F-2626 and turn the unit on, the relay clicks. Ideas?
     

     

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  2. ManyMoonsAudio

    ManyMoonsAudio AKA paul79 Sponsor Subscriber

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    Tuner working? You lost a voltage somewhere I believe.
     
  3. LBPete

    LBPete Rolling Along Subscriber

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    Where are you measuring the 4.3 volts? If you don't have a dim bulb tester, it's time to build one.

    - Pete
     
  4. G Heiman

    G Heiman AK Subscriber Subscriber

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    Location:
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    Yes, the tuner is working.

    I'm measuring the 4.3 volts at the speaker outputs.

    I have a dbt and a kill a watt and will report my findings.
     
  5. SanthoshA

    SanthoshA Active Member

    Messages:
    128
    The DC Voltage across the speaker output's seems to be very high.
    This could be the reason the relays are not engaging, the protection circuit might not send the voltage required for the relay to turn on when the DC voltage is present in speaker outputs.
    Have you tried replacing the DC Adjustment potentiometers too?
     
  6. stereoguy70

    stereoguy70 AK Subscriber Subscriber

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    4.3 volts at the speaker outputs is very high! Sounds like you have a shorted transistor in the power amp somewhere......the protection circuit is doing its job! Time to do some testing......
     

     

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  7. G Heiman

    G Heiman AK Subscriber Subscriber

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    No, I have not tried replacing the DC Adjustment Pots. I have spares in hand. I'll try that.

    I replaced the fuseable resistors on board F-2625 and have a question. The service manual shows R27,28 to be 4.7 ohm 1/2watt resistors. What I removed were 1 ohm and appeared to be factory installed. Which value should I use as replacement?
     
  8. G Heiman

    G Heiman AK Subscriber Subscriber

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    To steroguy70: Any suggestions as to where to start testing.
     
  9. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I think this is more likely to be a power supply problem, as you seem to say you have 4.3V at BOTH speaker outputs, but in any case checking the power supply voltages would be the first place to start.
     
  10. stereoguy70

    stereoguy70 AK Subscriber Subscriber

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    Are we absolutely sure that you are reading volts? Should be millivolts......what scale do you have your meter set to?
     
  11. G Heiman

    G Heiman AK Subscriber Subscriber

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    Yes, just double checked the voltage 4.3 Vdc.
     

     

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  12. stereoguy70

    stereoguy70 AK Subscriber Subscriber

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    I would think if the problem was with the power supply, every section would have issues and you'd have a lot more voltage out the speakers than you do. I still think you have a shorted transistor in the power amp somewhere, probably the output transistors.......unless this particular unit uses STK modules instead of output transistors, to which I would say there is a problem with the STK modules.
     
  13. mattsd

    mattsd AK Subscriber Subscriber

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    4.3 volts is normal to see at the speaker terminals on this model because they are floating with the relay open, once the relay closes it will drop to whatever the offset is coming out of the amp. Measure the voltage (ground referenced) at the relay terminals that are directly in front of the terminals for the coil, I circled them in photo below. You'll need to take off the bottom cover to do this.

    Also, replace the fusible resistors on F-2625 with the values that are on the board.
     

    Attached Files:

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  14. Goldie99

    Goldie99 Well-Known Member

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    If the protection relay is doing it's job, it should be disconnecting the speakers from any +4.3Vdc voltages coming from the main amps.

    I wonder if the 4.3Vdc is not entering the circuit(s) after the relay - the Vdc sensing point is actually after the relay according to the schematics. That would also explain why the DC offset adjustment has no effect. As others have said, with 4.3Vdc on both channels, I'd look for what's common to both channels.

    On the fusibles:

    The service manual schematic at the hifiengine.com website shows R27 & R28 on F-2625 board to be 1R 0.5W, as you indeed found. The parts list in the same manual is different, showing 4.7R 0.5W - I'd stick to what's installed on the board, namely 1R 0.5W. It's not uncommon to find manual errors, so the usual 'rule' is to stick with the values already on the board (that you know must have worked fine previously).
     
  15. G Heiman

    G Heiman AK Subscriber Subscriber

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    Thanks for the info. guys. Much appreciated.
     
  16. G Heiman

    G Heiman AK Subscriber Subscriber

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    Took some time off to watch the Big Ten tournament yesterday and order some 1 ohm resistors.

    Goldie99, I looked at the schematic in the back of the service manual I have and it shows the 1 ohm resistors on R27,28. Same thing with R4 on F-2626. Parts list shows 22 ohm, actually 4.7 ohm as the schematic shows.

    Mattsd, I'll measure the relay voltages and report them today.
     

     

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  17. G Heiman

    G Heiman AK Subscriber Subscriber

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    Mattsd, the measured voltages at 9 and 12 per your drawing are 4.3 Vdc.
     
  18. mattsd

    mattsd AK Subscriber Subscriber

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    Okay, what are the voltages at 5 and 8?
     
  19. LBPete

    LBPete Rolling Along Subscriber

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    Another way to do this is to measure from chassis ground to R21 and R22. These resistors are located on the power supply board and are in the signal path before the speaker/protection relay.

    - Pete
     
  20. G Heiman

    G Heiman AK Subscriber Subscriber

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    Location:
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    The voltage at 5 is -7.7 Vdc. At 8, it started at -7.3 Vdc, but over a couple of minutes dropped -.4 to 0 Vdc.
     

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