CR-800 Pop at shutdown revisited

Discussion in 'Yamaha' started by jandajr, Aug 30, 2018.

  1. jandajr

    jandajr Member

    Messages:
    80
    Location:
    Las Vegas
    With the help of several AK members I was able to completely restore a CR-800. During that restoration I posed the question about popping at shutdown. I was informed that having any burnt lights might be the cause. Replaced all the bulbs, problem solved. I have been enjoying my 800 with the exception of the cabinets damaged veneer. So I decided to re-veneer the entire cabinet. While having the cabinet off I also decided to upgrade to LED lights. Since changing to LEDs the popping has returned. Re-attached the original bulbs, dead silent at shutdown. What gives? below are the two diagrams I used for the new LEDs
     

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  2. avionic

    avionic " Black Knights " Subscriber

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    How did you wire the diodes? Both ways? Series and individually?
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,159
    Location:
    Fort Dodge, Iowa
    Your first screenshot with the three wired in series. I believe they need to be wired in parallel.
     
  4. jandajr

    jandajr Member

    Messages:
    80
    Location:
    Las Vegas
    I wired the three meter lights in series.
    I will wire them in parallel, and see what happens.

    Thanks again
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,159
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    Look over the schematic at how the incandescent lamps are wired.
     
  6. slow_jazz

    slow_jazz Lunatic Member

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    Try hooking the speakers up to the B terminal instead of A terminal.

    On my Pioneer SX-450 that solved my problem.
     

     

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  7. jandajr

    jandajr Member

    Messages:
    80
    Location:
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    I re-wired it in parallel and everything is back to normal, no pop!
    I followed the chart on how to determine what resistor to use, my mistake.

    Thanks again for your help.
    IMG_1340.jpg
    Above is a photo of the 800s cabinet with its new veneer and painted grille.
    I believe Yamaha receivers look better in a lighter color.
     
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  8. jandajr

    jandajr Member

    Messages:
    80
    Location:
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    When I first tested the LEDs, I turned the receiver on and off a half dozen times.
    After running it for about 10 minutes, I shut it down and it popped.
    I let cool down for ten minutes, tried it again, no pop. I can't win.

    It's no way as loud as it was originally, but still noticeable.
     
  9. amr2

    amr2 Well-Known Member

    Messages:
    502
    You can wire the LEDs in series with the advantage of less dissipation in the resistance. I have used arrays many times without any problem.
     
  10. amr2

    amr2 Well-Known Member

    Messages:
    502
    I would avoid putting several Leds in parallel with only one current limiting resistor. You can have inconsistent brightness. Use a resistor for each led if you don’t want to use a series array.
     
    Last edited: Sep 7, 2018
  11. amr2

    amr2 Well-Known Member

    Messages:
    502
    The serial array draws less current, this can be the origin of the problem.
     

     

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  12. jandajr

    jandajr Member

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    80
    Location:
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    Running the LEDs in series did cause the problem. I'm now using a resistor for each LED in parallel. As a stated earlier, no popping until it heats up.
    I checked the voltage and I'm getting +15.31 instead of 12 volts, at the two terminal. When I rebuilt the power supply I replaced all the diode and caps in that circuit. I don't believe 15.31 volts is correct. If so then I have to replace the resistors from 470 ohm to 680 ohm. Any thoughts on the 15.31 volts? The resistors are also getting hot to the touch.
     
  13. llwhtt

    llwhtt Super Member

    Messages:
    1,443
    Location:
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    The protection/relay circuit relies on the current draw of the incandescent lamps to operate correctly. The LEDs draw far less current and the power supply doesn't collapse as quickly at turn-off. The four parallel lamps draw 240ma, what you need to do is supplement the current draw of the LEDs with a parallel resistor that will get you back to or close to the original 240ma. Another possibility is to make C822 smaller so the power supply collapses quicker though I've never tried that.

    Craig
     
  14. jandajr

    jandajr Member

    Messages:
    80
    Location:
    Las Vegas
    I'm still puzzled as to why the voltage is 15volts vs 12. I re-checked FR807, D811, C821, and C822. Any thoughts?
    I'm going to re-do all the LEDs with 150 ohm resistors, to get me to 240ma at 15 volts.

    Thanks Craig
     
  15. llwhtt

    llwhtt Super Member

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    1,443
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    Basic electronics, less current equals higher voltage. The LEDs don't draw as much current as the lamps, as current draw goes down voltage goes up.. You need to calculate your series LED resistors based on the original 12VDC since that's what the voltage will be when the correct amount of current is drawn. Not sure what LEDs you are using so let's say we have a 2 volt drop across the LEDs and 10ma for each LED. So you need to drop 10 more volts at 10ma, 10/10ma equals 1,000 Ohms. Using your 150 Ohm resistors would give you 66ma per LED, I don't think they would last very long at that current. Now after all of the LEDs are connected we're only drawing 40 ma and we need 240ma or so. We need to draw 200ma more from the supply. 12V/200ma is 60 Ohms.at about 3 Watts. Find something near 60 Ohms @ 3 W. This is all based on 2V/10ma LEDs, what LEDs are you using? It's all in the math!

    Another thing, the 12VDC is based on 120VAC coming out of the wall. This supply is not regulated so it will vary with whatever is coming out of the wall.

    Craig
     
    Last edited: Sep 10, 2018
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  16. jandajr

    jandajr Member

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    Location:
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    Here's the calculator I used with my specs.
     

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  17. llwhtt

    llwhtt Super Member

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    OK, the calculator works fine as long as you punch in YOUR specific LED specs. Your LEDs have 3.3V forward drop? You're going to run them at 20ma? Did you notice the 25ma max.? So your 66ma is way over the max. Anyway my math ends up the same as the calculator. Somebody mentioned earlier that using one resistor causes varied brightness amongst the LEDs.

    So at 3.3V forward voltage and 20ma per LED you'll need a 75 Ohm 3 Watt resistor to make up the needed current draw.
     
    Last edited: Sep 10, 2018
  18. jandajr

    jandajr Member

    Messages:
    80
    Location:
    Las Vegas
    Yes, the LEDs current is 20ma, with a 3.3 forward voltage.
    I thought I had to use a resistor for each LED? I'm I wrong?

    Sorry that I didn't give you enough info.
    In the Yamaha CR-800 the tuner indicator light is connected separately from the three meter lights.
     
  19. llwhtt

    llwhtt Super Member

    Messages:
    1,443
    Location:
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    All four are connected to the same place in parallel. OK, 12V - 3.3V is 8.7V, we need to drop 8.7V at 20ma, which is 435 Ohms per LED, 470 Ohm is common, 1/2 W is plenty. With the 470 Ohm resistor we'll have 18.5ma, close enough. So now we have 80ma total LED current draw but we need close to 240ma, so we need 160ma more. 12/.16 = 75 Ohm @ 2 Watt, use at least 3 Watt resistor, 5 might even be better.
     
  20. jandajr

    jandajr Member

    Messages:
    80
    Location:
    Las Vegas
    Great.
    I'm already using a 470 Ohm resistor on each LED, so all I have to deal with is the 75 Ohm resistor.

    I've attached a copy of the circuit board layout. Seeing that I'm adding one resistor, does it matter if I connect the resistor to either of the 12+ locations.
    In parallel correct?
     

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