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A-700 Restore

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

  1. avionic

    avionic " Black Knights " Subscriber

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    Is it standing on end and greenish in color ?
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    42,768
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    Look at the schematics legend. for the resistor type identification chart. Lower left side grid F-G / 1.
     
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  3. Scottfer55

    Scottfer55 Member

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    93
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    No it’s laying flat 3BEB8E29-A460-48E9-AFDB-BA559F337E1A.jpeg
     
  4. Scottfer55

    Scottfer55 Member

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    The chart indicates a carbon film resistor
     
  5. avionic

    avionic " Black Knights " Subscriber

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    42,768
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    Unless specified in the schematic.or parts list. Its a 1/4 watt carbon film.
     
  6. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    That's just a normal carbon film 1/4w.
    Color code matches 4.7kΩ as you said.

    You can use this.
    The wattage isn't too important for resistors other than the fusible/flameproof ones (where it's more critical).
    For the normal carbon film resistors as long as the wattage is equal or greater (and the dimensions are the same) you're good to go.
     
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  7. avionic

    avionic " Black Knights " Subscriber

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  8. Scottfer55

    Scottfer55 Member

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    Apparently some resistors aren’t listed on the parts list for this amp. Thanks for the help
     
  9. avionic

    avionic " Black Knights " Subscriber

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    Location:
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    This tip was only for fusibles with given resistance and current ie milliamps.. Thats it..End of story.. I don't see any so far in the A-700 schematic.
     
    Last edited: Mar 7, 2018
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  10. avionic

    avionic " Black Knights " Subscriber

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    If there not listed .. Carbon film 1/4 watt.
     
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  11. Scottfer55

    Scottfer55 Member

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    93
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    Thank you, I’m starting to get a little understanding about how to navigate around. It would help if I printed that schematic. I will work on that tomorrow. I really appreciate your help
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

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    The fusibles in this unit. Will be standing elevated above the board. Either on end like the greenish ones. Or length wise. But above the board.
     
  13. Scottfer55

    Scottfer55 Member

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    Ok my misunderstanding, it’s good for me to re read some posts. Also thanks for nudging me to look at the schematic that’s what I need to be doing more of
     
  14. avionic

    avionic " Black Knights " Subscriber

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    Whats wrong with R271 ?
     
  15. Scottfer55

    Scottfer55 Member

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    The corrosion from the old glue is pretty bad on that one
     
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  16. avionic

    avionic " Black Knights " Subscriber

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    Good idea.
     

     

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  17. Scottfer55

    Scottfer55 Member

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    I’ll add some BAV-21’s to my order, after looking at some of these solder joints I’m surprised I had sound at all
     
  18. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    The following are all the corroded parts I’m going to replace.
    R271 cfr
    R338-341 mfr
    R373 cfr
    R367-369 cfr
    R274 cfr
    D149,D150

    I have one corroded flameproof resistor I’m having trouble finding a part number for, its R335 22ohm one of the standing with turquoise leads. Any help would be welcome and I will be able to submit the order.

    I’m using carbon film 1/4 watt on all with the exception of the metal film R338-341 that @zaibatsu was so kind to link the part no.

    The zeners are also from a link from zaibatsu.

    I’ve added the bav21 diodes to my order as suggested.

    I did receive the mk-168 transistor tester from China that I ordered off eBay for cheap, recommended on another post and tested a 2sc3370 transistor out of circuit with these results
    NPN 123=ECB
    B=67 uf=538mv
    What do these numbers tell me?
     
  19. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    You can use this for your 22Ω (fusible, flameproof). It's 1/3W instead of 1/4W but close enough.
    Everything else sounds good.

    On your tester:
    B = beta = hFE (gain)
    Uf = Vf (forward voltage, same as you would read on your meter in diode test mode)

    Be careful with those output transistors, they can't be replaced in exact spec anymore.

    Also, to echo what OMGCat said earlier, be careful with those bias transistors that were mounted on the heatsink. The legs are usually brittle with heat cycling and any bending can crack them and take out the output stage from thermal runaway. It's probably worth adding 2x BD135-16S to replace them in future, just leave them for now if they are intact, but for the future if you start poking around in there to recap etc.
     
    Last edited: Mar 8, 2018
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  20. avionic

    avionic " Black Knights " Subscriber

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    Last edited: Mar 8, 2018
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