Sansui AU-5900 power light question

Discussion in 'Exclusively Sansui' started by franclou, Jun 26, 2017.

  1. franclou

    franclou New Member

    Messages:
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    Hello,

    I changed the relay and some transistors in the AU-5900, everything is working fine (sound is amazing), but since I unplugged and replugged the red led indicator, it doesn't always light up. The machine can be on for an hour and then it lights up, other times, it lights up when powered on and then the light goes out. Doesn't affect the sound quality at all, I was just curious.

    Thank you in advance.
     
  2. LBPete

    LBPete Rolling Along Subscriber

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    Is it an LED or a bulb? If it's a bulb, it's not uncommon for solder points to fail due to the many heat and cool cycles when the amp is turned on then off. It may just need to have the solder reflowed.

    Please post the serial number for the database. Click on the link in my signature block.

    - Pete
     
  3. franclou

    franclou New Member

    Messages:
    24
    Thanks for the answer Pete, here are two pictures I took of the light.

    The serial number has been scratched by a previous owner, sorry about that. IMG_20170629_072407.jpg IMG_20170629_071540935_HDR.jpg
     
  4. LBPete

    LBPete Rolling Along Subscriber

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    That's an LED. The power for that LED passes through R601 on the power supply board (F-2596). Check to see if the voltage there behaves normally.

    - Pete
     
  5. JLange2010

    JLange2010 AK Subscriber Subscriber

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    I have the same amp with the same behavior. I'll be curious to see how this turns out!
     
  6. franclou

    franclou New Member

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    Hey Pete ! Thanks a million, gonna look at it this weekend. The connection looks loose though, the LED "legs" are passing through the connector.
     
  7. franclou

    franclou New Member

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    Hey Pete, R601 gives me 2,20 with my multimeter, which I think is fine ? The LED does'nt light at all now after I played with it, is there a way I can replace it ? Thank you very much.
     
  8. LBPete

    LBPete Rolling Along Subscriber

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    It would be very unusual for one of those LEDs to fail. When you say you have 2,20 with your mulitmeter, what are you measuring? is this voltage across the two terminals in the connector? Is the unit turned on when you are measuring? Is this 2.2 volts or millivolts or ohms?

    - Pete
     
  9. franclou

    franclou New Member

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    I measured the resistance on R601, I took it out of the board. It's 2.2 ohms. In the connector, it seems I don't have any current at all, machine on or off. I put the red sensor of the multimeter in the red opening of the connector and the black in the white. Newbie here ... it shows I think !

    Thanks again
     
  10. LBPete

    LBPete Rolling Along Subscriber

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    Its not 2.2 ohms, it's 2.2K ohms which is 2,200 ohms. The K is a multiplier x 1000. The resistor is good but do you have voltage to the connector? Measure the DC voltage between pins 12 and 13 on board F-2596.

    - Pete
     
  11. franclou

    franclou New Member

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    24
    The DC voltage between the two pins is 38.75 V.

    Thank you
     
  12. franclou

    franclou New Member

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    So, if I resume, there is power in the pins 12 and 13 but no current at all in the connector (white box) to the LED. So, I should replace the connector ? Thanks.
     
  13. LBPete

    LBPete Rolling Along Subscriber

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    If you have power at pins 12 and 13 but no power at the connector, either the wire between the pins and connector is damaged or you are not making good electrical contact with the meter probes. Your meter should have a "diode test" function. You can test the LED the same way you would test an ordinary diode. Connect the meter probes to the diode's two terminals and note the reading on the meter. Then revers the two probes and not the reading again. It should read zero in one direction and something like 0.650 in the other direction.

    - Pete
     
  14. franclou

    franclou New Member

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    I have no nothing on the LED, OL on both end. However, I have DC voltage on the connector when I take the time to put the meter probes wisely. So, it looks like the LED is bad ?

    Francois
     
  15. franclou

    franclou New Member

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    24
    Me again Pete ! I bought a new LED indicator for 35 cents. When I plug it in the connector, it doesn't work. But, if I play with it a little bit, it lights up, then the second I let it go, it goes off. I guess there is something wrong with the connector. When I test this new LED with the multimeter, it lights up right away. The LED in the machine seems dead.
     
  16. franclou

    franclou New Member

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    Pete, I replaced the LED and the connector. The LED will work for about one or two minutes, then it goes off. I'm clueless now. Thanks again.
     
  17. LBPete

    LBPete Rolling Along Subscriber

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    LEDs are directional. Since the supply is a DC voltage, the LED must be installed with the anode to pin 13, cathode to pin 12. If that's not it, there is one of two things going on. 1) The replacement LED may have a different current/voltage requirement than the original. 2) The power supply circuit is not dropping the voltage to the LED. Since the original LED is dead, lets concentrate on the replacement. The replacement LED should have a current and voltage specification. With that information you can calculate the value of the resistor that needs to be in series with the LED.

    Here's a link to a calculator to determine the new value for resistor R601. You measured about 40v supply voltage. The forward voltage and forward current values should be supplied with the LED. It should be on the package the LED came in. The original resistor is 2,200 ohms, what value resistor does the calculator recommend for the new LED?

    - Pete
     
  18. franclou

    franclou New Member

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    I'm learning so much stuff, thank you a lot for your patience and kindness Pete !

    The anode and the cathode are on the good pins, like I said, the LED goes on then stops after a minute or so.

    The forward voltage is 2.2V and the forward current value is 20ma. With the calculator (I found the link), it says that the resistor should be 1,890 ohms. Is that possible ? I tried to calculate the colors of the resistor on the Digikey website, but I'm not so sure.

    Thank you !
     
  19. LBPete

    LBPete Rolling Along Subscriber

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    10,932
    Location:
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    1,890 ohms is correct. The original resistor at 2,200 ohms may be a little too high for your new LED. It won't cause any damage but may cause the working voltage to be too low. Can you get a 1/2 watt resistor around 1800 (1.8k) ohms?

    - Pete
     
  20. franclou

    franclou New Member

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    24
    I had a 1.8kohms 1 watt at hand, the LED was lit for a minute before shutting down again. I can order a 1.8kohms at 1/2 at Digikey. Can the difference in watts make the difference ?

    Thank you
     

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