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Help with a Yamaha RX-V640

Discussion in 'Troubleshooting and Repair' started by Jeanguypataterubberboot, Dec 8, 2017.

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  1. Jeanguypataterubberboot

    Jeanguypataterubberboot

    40
    2
    Jul 9, 2013
    Hi there, I have a Yamaha RX-V640 that I have had for years and most of it's life has been in storage. When I turn it on it comes on for 1 second then turns off. I downloaded the service manual and got it to turn on in diagnose mode. I get the message "PS PRT 18% F". I connected it to a Variac and when I dial it down to less than 115 volts as opposed to the full 120 volts it powers on normally. This leads me to believe that it is a power supply problem. Here is the confusing part. When I measure the output of the Power Supply at 120 volts in diagnose mode the readings are about 3 volts low from the schematic. Nothing that I saw looks burned. I have very limited electronics knowledge so I am learning a lot here but I would love to fix it. I have an oscilloscope but don't have an isolation transformer so I don't dare use it as I heard that could create smoke in the scope.

    Thanks in advance for the help.

    Pierre
     
  2. 73's de Edd

    73's de Edd

    2,889
    1,224
    Aug 21, 2015
    Sir Jeanguypataterubberboot
    • 1. Your Avatar is giving me one HELL of an EVIL eye !
    • 2. With Jeanguypataterubberboot as your identity, it seems for sure, that you must have one HELL of a password that goes with that.
    Would the unit then stay on and play at that slightly reduced AC power input voltage ?

    Got milk? . . . . . . and that units Yamahauler manual ?

    Consulting that manuals page 91, note that the top left corner is devoted to LEFT main power amp and is being signal FLOW ARROWED in CERISE.
    Note that the two output transistors emitters merge and join into a dual 0.22 ohm emitter resistor.
    That joined output line passes to the right and past Q130 transistor above, and then to a union of one central inductor and a resistor above and one below. Our resistor of interest is the R187 / 68K resistor.
    As you look down at each of the 5 different power amp sections below, you will find the same relative part being replicated in each of their stages.
    Then the first one down is R191, then you have R194---- R198 and a final R202 on the very bottom amp.
    You now need to locate those on the circuit board of the unit and use a Sharpie to draw an oval around each of them to facilitate speedy relocation . ALSO put a large dot on the circuit board near the resistor lead that goes to the first units L102 and R190 connections, located just below it on the schematic layout.
    Then do that dot on all of the other corresponding resistors one lead.

    Standing by . . . .

    73's de Edd
     
    Last edited by a moderator: Dec 13, 2017
  3. Jeanguypataterubberboot

    Jeanguypataterubberboot

    40
    2
    Jul 9, 2013
    Actually he's a friendly kid. lol
    That name has been with me since 1987. I'll never forget it.

    I have located the resistors on the board. the sharpie doesen't work that well on the brown board though But I'll be able to relocate them.

    What next?

    Thanks for the help
    73
     
  4. Jeanguypataterubberboot

    Jeanguypataterubberboot

    40
    2
    Jul 9, 2013
    Actually after taking most of it apart and putting it back together it works fine now. It must have been a bad connection. Woohoo. Now I can sell it.
     
  5. 73's de Edd

    73's de Edd

    2,889
    1,224
    Aug 21, 2015
    Sir Jeanguypataterubberboot . . . .
    The next step would have been to place a DVM in DC Volts AUTO / OR / 50VDC range and have its neg probe to ground.
    Then you power up and and probe each of the "dot" marked points and log down that voltage found on each resistor.

    73's de Edd
     
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