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Yamaha RX-497 turn on problem.

Discussion in 'Yamaha' started by vanakaru, Apr 30, 2018.

  1. vanakaru

    vanakaru New Member

    Messages:
    44
    I got this receiver as non working - basically off the dumpster. I thought to give it a try or salvage some parts from it. For instance power caps are audio grade and rather nice when healthy.
    So it did not turn on - buttons did not do a thing. I had read about the 0.022uF capacitor along the relay being the problematic. And so it was, showed just about 5000pF. After replacement this cap, relay clicks happily when I push the power button, but nothing happens and after a sec. or so I hear feint click relay disengaging.
    I tested visually and with the multimeter all I could think of but can not find the cause. 10.5V power schema is there and power buttons work as expected.
    Then I just bridged the relay switch part to give constant power to to the power tranny. And BANG!!(pun intended) the thing starts working. However as soon I disconnect my bridging all is as dead as before.
    I have been running this for some days now and all the functions work - even the power buttons(main and standby) switch the amp on/off. Only it is not really off, is it.
    Tried factory reset thinking that maybe the memory chip was thinking about safe mode still - no go.
    I like the sound of this amp a lot. Specially pure direct is brilliant and enjoyable.
    So this is a keeper for sure. Thus would be nice to get it to work as it should - without the hardwired relay.
    Can you think of something to do about it with limited skills and equipment(just the soldering iron)?
     

     

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  2. vanakaru

    vanakaru New Member

    Messages:
    44
    Can someone tell me how the params in DIAG mode will be set. I can tweak these ok, but after re-powering all comes back as unchanged.
    Since this amp is working without noticeable problem I am pretty sure the protection modes need reset to solve the power-up.
     
  3. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

    Messages:
    4,105
    Location:
    Munich, Germany
    If you have checked for DC on the speaker outs and know for sure that you aren't pumping Dc to your speakers then I would start with:

    The relay itself. Check that the contacts aren't burned or oxidized.
    Bad solder connections in the protection section.
    Bad cap(s) in the protection section.

    I don't think that there is such a thing as a "protection mode reset". If there is DC voltage at the speaker posts the protection relay is supposed to open and there shouldn't be any option to override it. That's a good thing.

    If the relay is opening for any other reason then there is a problem in the protection section.

    Cheers,
    James
     
  4. vanakaru

    vanakaru New Member

    Messages:
    44
    There is no abnormal DC at the speakers - about 25mV.
    I did replace cap(C254) that is common problem with these amps. It was bad without a doubt. The relay itself seems to work properly - it gets 13-15V and turns on then after a second or so voltage drops to 0 and relay switches off. However when this relay is bridged there is no voltage drop and relay stay on.
    The protection detects voltages from 0-5V and you can set the range what will trigger shutdown i.e. 2-3V(drops under 2 or goes over 3). I was going to set these as maximums 0V and 5V just to test what protection procedure triggers the switch(DC, temp, PowerSupply overload). But I do not know how to set this change I made. After restart all params are the same as before.
    I have seen that more parts would be replaced in protection section - flipflop IC252, transistor Q254 and some diodes. Before I do that I want exhaust easier options.
     
    Last edited: May 8, 2018
  5. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

    Messages:
    4,105
    Location:
    Munich, Germany
    I found a very nice quality service manual pdf at vintagehifi.com.
    https://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Yamaha-RX-497-Service-Manual.pdf

    I guess that you have that or another copy of the SM. It surprised me to see that there really is a protection history and reset function, see page 11 for info about clearing it. Page 12 shows Factory Reset. I have to print this thing out and look at it a bit, this is way outside of my experience.

    One thing that is in my experience with Yamaha amps is bad solder connections. I'd probably start re-touching all of the solder connections in the protection and power supply to start with. And if you have already found 2 bad caps there are probably more.

    Cheers,
    James
     
  6. mbz

    mbz AK Subscriber Subscriber

    Messages:
    2,072
    Location:
    Melbourne, Victoria
    I would be strongly against bypassing the amps protection, some of the protection is rather abstract and go beyond just dc at spkrs.
    Suggest read protection history as per @Bratwurst7s, pages 10&11. It may be something simple like a tired cap in the regulated
    supply causing the voltage to dip out of spec or ...
     

     

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  7. vanakaru

    vanakaru New Member

    Messages:
    44
    I ran DIAG
    3. AD DATA CHECK
    K0/K1
    The only keys that are giving values not in the range are
    SPEAKER B - 71
    SPEAKER A - 100
    Do I understand this right that I need to check this switch/key panel for possible bad solder joints and resistors.
    Also there is a history in
    6. PROTECTION HISTORY
    that I can not understand
    6-1 TmRPRT 000
     
  8. mbz

    mbz AK Subscriber Subscriber

    Messages:
    2,072
    Location:
    Melbourne, Victoria
    What is the first message you get when you enter diagnostic mode.
    It should be one of the following,

    NO PROTECT ...
    I PROTECT ...
    PS PRT ...
    DC PRT ...
    TMR PRT ...

    Reply post what the first line is, need the complete line, all characters.
     
  9. vanakaru

    vanakaru New Member

    Messages:
    44
    Mine reads just as I wrote:
    6-1 TmRPRT 000
    According to the manual it should be at least like this:
    6-4(not 6-1) TmRPRT .....and some numbers other than 000 to indicate value. That I do not understand. Maybe this means that the sensor on R channel heatsink is not working?
     
  10. mbz

    mbz AK Subscriber Subscriber

    Messages:
    2,072
    Location:
    Melbourne, Victoria
    Yeah, it can be a bit tricky, the history may have been accidently cleared
    or the threshold is incorrectly set.

    1. Attempt to power on the RX normally
    2. Enter DIAG mode "MASTER" + "FM/AM" + "8" Keys
    Confirm first message displayed is 6-1 TmRPRT 000
    3. Access the AD DATA CHECK menu by pressing station preset button "3"
    4. Try to find sub-menu THM L,R using the Tuning "Forward" or "Reverse" buttons
    Record any numbers
    5. Access the PROTECTION SETTINGS menu by pressing station preset button "5"
    6. Try to find sub-menu TEMP using the Tuning "Forward" or "Reverse" buttons
    Record any numbers. Since only the right channel is monitored the left
    threshold is zero L000, the right should not be zero, ie, not R000

    As a last resort there is a factory reset procedure however you will loose
    some settings, best to wait on this step. Suspicion is the temp threshold is
    incorrectly set (to R000)
     

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