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Yamaha receiver won't turn on

Discussion in 'Troubleshooting and Repair' started by Rick79, Nov 6, 2017.

  1. Rick79

    Rick79

    268
    3
    Nov 26, 2014
    1996 Yamaha RX-V795a

    I bought this receiver at a yard sale. Before buying I was able to test it. It powered up and I tested all channels and everything was working. The next day I tried powering it up and I noticed it would shut off right away in about a half second. I have another receiver that is the exact same model and it was having the same issue, the contact in the relay was worn and I just needed to replace it.
    So i removed the cover to inspect the power relay switch and it does have continuity. The switch just doesn't stay on. Could the cylinder on the switch be bad? I don't wanna try holding it down and possibly burn something out. Is there any other components on this board that could cause of this problem? I don't have a capacitor tester, but I do have a multimeter.
     

    Attached Files:

  2. Rick79

    Rick79

    268
    3
    Nov 26, 2014
    Update: I swapped power boards with my other RX v795a and that receiver turns on. So everything on the power board is good. What could possibly be wrong? it was working at the yard sale when I bought it but not here at home.
     
  3. HellasTechn

    HellasTechn

    1,407
    195
    Apr 14, 2013
    I repaired a Yamaha RX-V795a about 6 months ago. I cant really remember what was wrong with it. One thing i do remember is that there was a problem with the fan running at very low rpm and the amp was overheatig.

    I The protection kicks in if something is wrong in a number of places on the board.

    You say you checked the relay. How ? The proper way of checking a relay is to remove it from the board, then measure the contacts at that state, then apply the appropriate voltage to it's coil and then measure the contacts
    again.

    First thing i would do is check the power supply for bad regulators. Then check the power transistors at the output state.
    P.S. I do not remember the location of the Vregs...

    You may also want to take a look here:

    https://www.electronicspoint.com/threads/yamaha-rx-v795a-receiver-doesnt-power-on.272207/
     
  4. Rick79

    Rick79

    268
    3
    Nov 26, 2014
    Oh Yeah, that post was me repairing another Yamaha RX V795a.

    I checked the relay applying 12v and it made good contact, plus I installed the whole board into my other RX V795a and it powered on no problem.
    I was just wondering if there was something else I could test before taking everything apart looking for bad transistors and cold solder. I hear that some power transformers have thermal fuses that go out on some yamahas. I don't know how to check for that or how to test the transformer.
     
  5. kellys_eye

    kellys_eye

    4,284
    1,145
    Jun 25, 2010
    What do you mean by 'good contact'? What is your criteria for determining this? Did you actually check the contact resistance?

    Where is the cover for the relay?

    If it has been exposed for any length of time I'd be cleaning those contacts and/or replacing the relay.

    You can test at D822 (small square bridge rectifier) for AC at the relevant ~ pins and DC at the +/- pins.

    Note, since the bridge rectifier doesn't actually show the ~ markings you can take it as read that they must be the ones that AREN'T marked +/-......
     
  6. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    Sir Rick79 . . . . .

    Verily, verily now I ask thee . . . . .

    Is it to be the relay . . . or is it not to be the relay . . . .

    On the schema snippet with the power relay, I have marked up the area of concern.
    The relays coil and spst contacts for power switching are highlighted in YELLOW.

    DC metering mode . . . Negative meter probe to anywhere along the BLACK DOT ground buss

    Voltage probe initialy to the RED dot to see if the regulated 9 VDC is there .
    Then power on the unit to see if that voltage holds or significantly pulls down, and if the relay clicks and pulls in.
    If the relay is then dropping out . . . then meter at the GREEN dot to see if that .7 v holds until the relay drops out.
    If that .7 drops off . . . . . then the relay associated trouble is being elsewhere.

    Waiting for your tests before progressing in the next logical test sequence and area.

    REFERENCE SCHEMATIC SNIPPET OF POWER RELAY CIRCUITRY . . . . .

    YAMAHA POWER RELAY CKTRY.png

    73's de Edd
     
    Last edited by a moderator: Nov 7, 2017
    Dougnsalem and HellasTechn like this.
  7. Rick79

    Rick79

    268
    3
    Nov 26, 2014
    Hi edd
    I have two Yamaha RX-V795a Receivers. I removed the power supply board from the receiver that won't turn on and I installed it into the other receiver and it works just fine powering it up. So that means the relay and everything else on the power board is ok.
     
  8. Rick79

    Rick79

    268
    3
    Nov 26, 2014
    I removed the cover to inspect the contacts. I checked for resistance with my meter and there was no resistance. I also installed the power supply board into another Yamaha RX V795a receiver and it works, so it has to be something else in the receiver causing the 1/2 second shut down.
     
  9. 73's de Edd

    73's de Edd

    2,678
    1,085
    Aug 21, 2015
    OK then that means that you need to monitor the GREEN dot voltage on each unit and pass back the different voltages that are being experienced by both units.
     
  10. Rick79

    Rick79

    268
    3
    Nov 26, 2014
    4.75 Volts on the working Receiver & 4.58 Volts on the other receiver right before it shuts down. It only stays on for a half of a second.
     
  11. damianos

    damianos

    1
    1
    Nov 19, 2017
    Helo Rick i have exactly the same problem and the same voltage 4.5 volt for half second on power pcb relay.
     
    Rick79 likes this.
  12. Rick79

    Rick79

    268
    3
    Nov 26, 2014
    I tried the Diagnosis mode holding down the buttons "input mode" & "am/fm" while pressing the power button and I can see for a half a second it displays "PS PRT 14%” what does that mean?
     
  13. Rick79

    Rick79

    268
    3
    Nov 26, 2014
    Hey Damianos, Did you ever find the problem?
     
  14. KilgoreCemetery

    KilgoreCemetery

    231
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    Apr 12, 2017
    PS PRT is "Power Supply Protect".

    edit: It's telling you that there is a 14% voltage deviation
     
    Last edited: Jun 17, 2018
  15. KilgoreCemetery

    KilgoreCemetery

    231
    9
    Apr 12, 2017
    My google-fu turned up two more things:
    1. You should make sure the impedance selector switch in the back is set properly. Evidently it's easy to get the switch between settings on this model.

    2. Pulled this from a different site and the section I found in the service manual about error codes seems to confirm it:
    "All of the power supplies are voltage divided and summed to create one voltage that the CPU monitors. The error indicates the voltage in % of 5 volts that the CPU is monitoring. Because all of the power supplies are summed it is not possible to indicate which supply is in fault by the % reading. One of the supplies could drop to 20% of its normal reading but the CPU would not necessarily indicate a 20% change depending upon the voltage division of that particular supply. The supplies that the unit monitors are the main B+ and B- as well as most of the low voltage regulate supplies. The normal reading is not 100 percent but somewhere around 18-23 percent."

    Untitled.jpg
     
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