1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

A-700 Restore

Discussion in 'Yamaha' started by Scottfer55, Mar 6, 2018.

  1. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    On the power source 1 board (the one with the diode bridge) there is 45.5 vac from either red to black, should be power from transformer.
    I’m measuring 117vdc across the red (B+) and blue (B-) seems high... not sure where to look on schematic to see what it’s supposed to be but I’m pretty sure it is power to the main board.
    There is also on power source 1 board a
    Black (E) and white (DSC) wire. I’m measuring 52.3vdc across those.

    All measurements are taken while on DBT
     

     

    Please register to disable this ad.

  2. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    DC power supply voltages..
     
  4. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    Scottfer55 likes this.
  5. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Much better then what I’ve been using thanks, What am I looking for? I know your busy mr @avionic and don’t want you to stop what your working on. When you get a chance I could use some help if your up to it
     
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    Basically. We have to start all over.





    Dave
     
    Scottfer55 likes this.

     

    Please register to disable this ad.

  7. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    Measure the collector voltage of each of your output transistors.( B+ and B-). Both Channels.
     
  8. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    We are looking for + 71 vdc and -71 vdc ballpark. Probably be less with the DBT.
     
  9. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    B+ 58.8vdc
    B- 58.8vdc
    Both channels same
     
    avionic likes this.
  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    OK..Thats a good sign.
     
  11. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    TR151 (relay driver) Need to know the emitter,collector and base vdc's
     

     

    Please register to disable this ad.

  12. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    Also TR152's voltages.
     
  13. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    TR 151
    E .0
    C 58
    B .0

    TR 152
    E 0
    C 58
    B -3.6

    Updated
     
    Last edited: May 16, 2018
  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
    Check your solder connections on TR151,152 and relay RY101.
     
  15. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    They are good
     
  16. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Me @avionic, I’ve got to get up early for work. I’ll be back online tomorrow evening if your available. I sure do appreciate your time and hopefully we can start where we left off tomorrow. Thank you
     

     

    Please register to disable this ad.

  17. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,562
    Location:
    Fort Dodge, Iowa
  18. Hamish119

    Hamish119 Member

    Messages:
    91
    Location:
    London, UK
    As an armchair observer vicariously playing along at home, I'm concerned for the amplifier's safety. :lurk:
    Please verify your voltage measurements/supplied information.
    According to the circuit diagram, TR151's Emitter CANNOT be at a different potential to TR152's Base. :no:
    Yamaha_A-700_TR151andTR152.jpg

    I suspect that you've swapped/muddled the transistor designations: i.e. TR151 voltages are actually TR152 voltages and vice versa. :dunno: :confused:
    A picture of the transistor orientation is worth a thousand words.

    N.B. The assistance/answers you receive will, in most cases, be based on the information you supply. If you supply erroneous information, you'll destroy the amplifier. :blah:

    And...
    The DC voltage polarity indicators are NOT optional - please specify + or - with each DC voltage measurement. The DC voltages and their polarities should be measured with the black probe welded to the zero volt reference: i.e. the copper busbar or the black leads on the 22000uF capacitors. :blah:

    The following misleading information indicates a fault as both B+ & B- are at the same (unspecified polarity) potential. :whip::eek:
    Another example
    + or -? :dunno:

    As there's 36V of unknown polarity at the L & R relay contacts, it suggests that the problem is common to both channels.

    With your meter's black/negative lead welded (not clipped) to the 0V reference point, please measure (at both individual component leads) the voltage and polarity at C205, C210, D149 & D150.
    Please post the results.

    N.B. You don't need to weld the negative lead to 0V - clipping is sufficient. :rflmao:
    You must always use the bulb limiter (DBT) until ALL issues are resolved.

    BEWARE - There are several errors/inconsistencies in the circuit diagram!

    DO NOT assume that because you've replaced parts the issue is resolved. VERIFY! [​IMG]
    DO NOT use/select the PHONO input until the current issue is resolved. :no:
    DO NOT engage CLASS A until the current issue is resolved. :no:

    DO Engage the SUBSONIC filter - it will block any DC voltages coming from the pre-amp stages.

    Good Luck!
     
  19. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Thank you @Hamish119 for this post, one thing I have to do before I go any further is pick up a better set of leads for my fluke, I’m hoping to get that today if time permits after work. (Unlikely though as we are having a hospital power shutdown this evening). I know I need the electronics type leads with the sharp pointed end. I will review your post and follow up when I’m able to get back to work on it. Thanks again
     
  20. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

    Messages:
    4,210
    Location:
    Munich, Germany
    Are you doing a "pull the plug and see what happens" power test at the hospital? That's always stressful. We're doing ours next month. Good luck.

    Cheers,
    James
     

Share This Page