Need help with Yamaha R-900 any owners out there to take a pic for me?

Discussion in 'Solid State' started by saabracer23, Feb 5, 2018.

  1. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    741
    Location:
    Salem, Oregon
    I have an R-900 in front of me that has a burnt resistor and two more resistors in the same circuit that look pretty crispy as well. There is no way to read what the value was on the burnt one. It came from the empty space below.

    D040408B-6825-4F2A-A764-1B725403AF33.jpeg
    9B49F622-964B-48B2-9359-38297A7766B9.jpeg

    You can see the two resistors right above those transistors that look pretty toasty as well. I can’t get a value on those either, I can only get the colors on the two middle bands the two channels are not alike.

    The service manual and schematic are extremely difficult to impossible to read and what can be read seems to be wrong. The resistor that burned to a crisp, the service manual board layout had a diode in that position. The value for those other two resistors that look crisp according to the schematic are 680 ohm which they clearly are not since they have orange/white or orange/yellow stripes as the center stripes. I don’t even see 680 ohm resistors in that entire circuit.

    Anyways I was hoping maybe someone with an r-900 would be willing to pop the top and send some clear closeup photos of the two amplifier circuit sides.

    Dan
     
  2. Hufsredo

    Hufsredo Member

    Messages:
    57
    Location:
    Hanford CAli
    I bought an R900 for parts, Ill take a look.
     
  3. Hufsredo

    Hufsredo Member

    Messages:
    57
    Location:
    Hanford CAli
    That must be a common issue, those are fried on the left channel on the board iv'e got. On the crispy one I can see the first band is red with a 5% gold
    on the end. The green cased ones are either X white red or orange gold, you might be able to find something on the schematic that fits. I can post pics but they won't help much, the crispy one even burned the board.
     
    goodolpg likes this.
  4. Aspen

    Aspen Active Member

    Messages:
    311
    Location:
    London, Ontario
    I will look tomorrow
     
  5. Aspen

    Aspen Active Member

    Messages:
    311
    Location:
    London, Ontario
    Red red brown gold, decided to look through the vent in the cover. I have the service manual somewhere too. There's another crispy one at the top of your pic. Stk 1070 may be pooched. I posted a source for some nos ones a while back.
     
    Last edited: Feb 13, 2018
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,112
    Location:
    Fort Dodge, Iowa
    Look for the identical twins on the other channel.
     
  7. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,112
    Location:
    Fort Dodge, Iowa
    I'd be checking transistors and diodes in the immediate circuit of those resistors.
     
  8. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,112
    Location:
    Fort Dodge, Iowa
    That big black STK1070 II is suspect as well.
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,112
    Location:
    Fort Dodge, Iowa
    There should be two like them close to the other STK. Hard to say what color they are / were. They have been cooked. How many ohms do they measure ? Probably "open" like a fuse.( fusible resistor )
     
  10. telemike

    telemike AK Subscriber Subscriber

    Messages:
    2,178
    Location:
    Greensboro, NC
    I had an R900 in college back in the 80s. I smoked the power chip on mine. Ran hot.
     
  11. Aspen

    Aspen Active Member

    Messages:
    311
    Location:
    London, Ontario
  12. Aspen

    Aspen Active Member

    Messages:
    311
    Location:
    London, Ontario
  13. Aspen

    Aspen Active Member

    Messages:
    311
    Location:
    London, Ontario
    Having trouble getting a good shot uploaded.
     

    Attached Files:

  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,112
    Location:
    Fort Dodge, Iowa
    Whats the color code on those two green resistors close to the chip amp.
     
  15. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,112
    Location:
    Fort Dodge, Iowa
    Gold being the fourth band.
     
  16. telemike

    telemike AK Subscriber Subscriber

    Messages:
    2,178
    Location:
    Greensboro, NC
  17. Aspen

    Aspen Active Member

    Messages:
    311
    Location:
    London, Ontario
    Looks to be gold, brown, red, gold
     
  18. Aspen

    Aspen Active Member

    Messages:
    311
    Location:
    London, Ontario
  19. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    741
    Location:
    Salem, Oregon
    So yours are like the amp I have, on the one channel the two middle bands are orange and white!

    So the two channels aren’t identical, wish it was that easy.
    97C84112-12CE-461A-B08A-215CFEB74566.jpeg
    D253A4EC-8B3E-4682-9A21-0AAEC11AF0E5.jpeg

    In the other channel they are 820 ohm, which it looks like Aspen’s unit has in his channel. In his photo it appears I see a grey, red, brown, gold. Maybe it came from the factory different or it was worked on in its past. The ones in there are measuring in the mega ohms.

    I assumed the STK device was bad and suspected that the voltage amplifier may need to be replaced as well. Looks like I’ll just go with the 820 ohm resistors in both channels. The service manual calls for 680, to bad it’s nearly impossible to read. Did the manual come from Yamaha like that? There has to be a better document out there in the world.


    Thank you, much appreciated!

    Dan
     
  20. avionic

    avionic " Black Knights " Subscriber

    Messages:
    38,112
    Location:
    Fort Dodge, Iowa
    On the schematic they are. They are electronically identicle. Id´use the 820 Ω to replace those two french fried resistors.Layout on the board is different.
     

Share This Page