CR-420 right channel issues

Discussion in 'Yamaha' started by JPromo, Dec 31, 2017.

  1. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,316
    Location:
    uk.. the middle bit
    i always like a happy ending
     

     

    Please register to disable this ad.

  2. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,151
    Location:
    Fort Dodge, Iowa
  3. Chaulk61

    Chaulk61 New Member

    Messages:
    17
    Yep.......perfect fit....and only took two days to get from Texas to Hamilton, Ontario.
    Great service from Mouser.
     
  4. JPromo

    JPromo New Member

    Messages:
    18
    Unfortunately, the relay didn't do it for me. Must have just been coincidence when I smacked it that it cut back in.

    Checking the output transistors, all read a steady 30V at the base all the time. Across the E and C I had one in the right channel that was stone 0.0 while the others read 0.6v. Something caused the channel to cut back in and I got a chance to test the previously 0.0 E to C and it was a perfect 0.6V. Can an output transistor be intermittent? Because it's got good voltage at the base even when the channel is out.
     
  5. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,316
    Location:
    uk.. the middle bit
    i am pretty sure you have BCE mixed up a little .
    reading between the lines the output with 0v has maybe lost its drive .
     
  6. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,316
    Location:
    uk.. the middle bit
    look for cold solder joints
     
    avionic likes this.

     

    Please register to disable this ad.

  7. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,151
    Location:
    Fort Dodge, Iowa
    2nd the motion..
     
  8. JPromo

    JPromo New Member

    Messages:
    18
    I absolutely do. Collector voltage is 30v. I'm used to tubes, where my tester makes up for what I don't know.

    So I've got one output transistor with intermittent 0v across B and E. Randomly goes in and out, but smacking in the area of will regularly bring it back.

    Joints look good, none look broken or cold. Might be worth a reflow next time the iron is hot though.
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,151
    Location:
    Fort Dodge, Iowa
    Wiggle the part and watch the solder connection for any movement while your wiggl'n.
     
  10. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,316
    Location:
    uk.. the middle bit
    have had this with sockets . no idea if any socket connections with this unit .
     
  11. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,316
    Location:
    uk.. the middle bit
    narrow it down some if you just checked if base voltage is stable .
     

     

    Please register to disable this ad.

  12. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,151
    Location:
    Fort Dodge, Iowa
    Pay close attention to TO-220 and TO-126 transistors. They run warm/hot and over a long period of time they will develope annular ring cracks in the solder connection. Large resistors as well generally get warm and can generate enough heat over time to compromise the solder connection.
     
    Last edited: Jan 8, 2018
  13. JPromo

    JPromo New Member

    Messages:
    18
    Fresh solder on all TO-220 transistors didn't do it. Added star washers to all the brass screws holding the pcb and heatsink. Still cuts out in the right channel and tapping one of those right output transistors usually brings it right back.

    Next time I have the bottom cover off, I'll do a real close check on the transistor traces, then check solder at some other large components, but besides that, I don't know where to look. Can a transistor be intermittent? I know failure is typically catastrophic.

    Thanks for your input and patience!
     
  14. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,316
    Location:
    uk.. the middle bit
    yes anything can happen .substitution will confirm it .or not as the case may be . get in closer with a plastic prodder .
     
  15. JPromo

    JPromo New Member

    Messages:
    18
    I will go ahead and try subbing transistors.

    Searching through the forums, I saw the recommendation of TIP41C/TIP42C in place of my D525 B595 pair. Good option? How many should I buy to expect a decent pairing match?
     
  16. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,316
    Location:
    uk.. the middle bit
    no real need to match unless working in pairs or more ..
    others may disagree . i have never had a problem if ordered together .
     

     

    Please register to disable this ad.

  17. JPromo

    JPromo New Member

    Messages:
    18
    So should I just try and replace the two in the bad channel, or replace both pairs? I'm realize there could be conflicting views on this too.
     
  18. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,316
    Location:
    uk.. the middle bit
    i would get that one side working first then decide .. i bet if both sides working properly you wont notice any difference .
     
  19. JPromo

    JPromo New Member

    Messages:
    18
    Just got the output transistors installed for the right channel and that seems to have been the issue all along. Ran it for about an hour last night with nothing cutting out so I'm calling it solved. Thanks for all the help!

    For search reference--output transistors can be intermittent.
     

Share This Page