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Restore + Repair Yamaha C-2a & C-80 / M-80

Discussion in 'Yamaha' started by mr.muddles, Aug 25, 2018.

  1. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    I tried the last meter I have the built in one in my Tektronix scope and it gave me the exact same result...

    Something can't be right?
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,805
    Location:
    Fort Dodge, Iowa
    Ohms check D511 ( VD1212)
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,805
    Location:
    Fort Dodge, Iowa
    Yes, Something is really messed up in your pre-amp.
     
  4. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    According to my notes I put in:

    R529 - 2.7k
    R530 - 2.7k
    R531 - 39k
    R532 - 39k
     
  5. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    I just finished visually confirming that they are all correct... I did not measure them though... just looked at the markings on the case. I was pretty meticulous about the resistors... not to say it's not totally possible I made a mistake though...
     

    Attached Files:

  6. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    i forget to check which side was the anode/cathode

    but the readings were 385K one way and 9.3M the other way...
     

     

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  7. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    I've never measured a diode using ohms always use the diode test... Is this one toast?
     
  8. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    I'm guessing it is because its giving a reading in both directions... and yes, I pulled one leg from the circuit to take the reading
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,805
    Location:
    Fort Dodge, Iowa
    Probably OK.
     
  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,805
    Location:
    Fort Dodge, Iowa
    Yes, it's OK. I just verified one here. Got very similar reading.
     
  11. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,805
    Location:
    Fort Dodge, Iowa
    Way back when using an analog volt/ohm meter. That's how one had to measure diodes. Very high resistance one way and low resistance the other.
     
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  12. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    TR01
    B = +4.2V
    C = +36.4V
    E = +4.8V

    TR02
    E = +3.89V
    C = +36.29V
    B = +3.3V

    TR03
    B = +4.2V
    C = +36.5V
    E = +4.8V

    TR04
    E = +3.87V
    C = +36.4V
    B = +3.2V
     
  13. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    TR13
    E = +36V
    C = +40.13V
    B = +36.5V

    TR14
    B = +3.84V
    C = +36.3V
    E = +3.2V

    TR11
    E = +35.9V
    C = +40.13V
    B = +36.48V

    TR12
    B = +3.8V
    C = +36.4V
    E = +3.2V
     
  14. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    Looks like there's a problem with TR14 and TR12?
     
  15. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    I just did step 4 on the adjustment procedures in the service manual. This is the first time I've done this reading...I'm wondering if this was what I was supposed to be reading before and instead was giving the wrong one? anyways...the voltages are fluctuating wildly in the mV and V range -/+ on both channels TP1 to 2 and TP3 to 2 on the DC Offset Equalizer Section...does this mean my problems are outside the tone control board?

    I checked the power voltages again and they are still +/- 40V
     
  16. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    Step 2 Checking muting operations:

    TR262 is supposed to be 36V +/- 3V on the collector... I'm getting 28V.. was 28.6 and rose to 28.9V
     

     

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  17. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    The only things I did just prior to smoking switches and resistors:

    swapped TR527-530 from R to L channel and then back again

    Tested phono input using a turntable and small amp with headphones...

    Adjusted the resistance loading knob for the phono...

    Speaking of which, all of the selector switches are in unknown positions, same with the rest of the switches and pots... I have the cross bars off inside the the preamp that control the selectors..

    at this point the symptoms were still the same.. I might have noticed a start of the smell at this point but I could be remembering wrong...there was no smoke...

    put away the turntable stuff and was going to take measurements...noticed TR527 was getting really really hot and around this this time i started getting really wild readings on the tone control board between TP1-3 on both channels...

    this is when the smell started coming on thick and then gradually the smell became a small waft of smoke and then the smoke became almost instant...it seemed to be a gradual but steady escalation...the mode switch flipping onto stereo made the transistor TR527 get searing hot and when the mode switch was on stereo it seemed to accelerate the inevitable smoking...
     
  18. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    is it possible that the glue on the board is somehow becoming more active over time due to the heat and causing conductivity issues? i'm just spit balling i really have no idea what i'm talking about...

    there are a number of capacitors that have the glue and some jumpers that are covered in it as well. I have a full set if electrolytic capacitors that i have not installed yet because i thought it was better to wait to fix it before doing anything else... is there any sense in just recapping it at this point?

    no body seems to really be making in grave statements about the glue so i was going to wait to clean all of that up while i did the full recap...
     

    Attached Files:

  19. mr.muddles

    mr.muddles Active Member

    Messages:
    458
    Location:
    Portland, OR
    leaving the preamp on TR525 gets pretty hot... too hot to hold my finger onto... it's by far the hottest transistor on the tone control board..

    i think the DC offset for the equalizer might be in spec..adjusting the pots affects the reading.. it will not stay steady and drops into the -/+ mV range but looks like it mostly stays within 200mV but it will not stay steady and keeps jumping around...

    the idling current for the equalizer was within spec and steady.
     
  20. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,805
    Location:
    Fort Dodge, Iowa
    That glue will need to be eliminated and any corrosion addressed.
     

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