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Power supply overheating

Discussion in 'Power Electronics' started by Jimbert, Jan 31, 2021.

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  1. Jimbert

    Jimbert

    11
    2
    Dec 2, 2014
    Organ power supply.jpg Organ power supply1.jpg Organ power supply2.jpg
     
  2. Jimbert

    Jimbert

    11
    2
    Dec 2, 2014
    In my original post I neglected to add the text. The organ has no sound. All power supply voltages appear to be OK except the 23V supply measures 27V. The big mystery is that R1 overheats to 200+ deg, but only at one end. I've measures the temp with an infrared digital thermometer. If I position it to one end I get 79 deg. At the other end I get 200 deg. resistance of R1 measures 10 ohms. Not sure what's going on. Any ideas?
    Thanks,
    Jim B
     
  3. bertus

    bertus Moderator

    1,479
    584
    Nov 8, 2019
    Hello,

    Are the degrees celcius or fahrenheit?
    200 degrees fahrenheit is about 94 degrees celcius.
    What is the unregulated voltage mentioned as 53 Volts?

    Bertus
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,999
    2,502
    Nov 17, 2011
    Surely Fahrenheit as the op is from "murica".
    The difference in temperature between the ends may be due to the wider copper trace at the "cool" end that dissipated more thermal energy than the thin trace at the "hot" end. Although the difference is quite high. Possibly the IR theermometer wasn't correctly aligned and measured the temperature of the PCB partly?
    Anyway, 94 °C is not yet to be worried about.
    Just a note on the side: Going from 53 V to 27 V via a linear regulator is not the best design decision. No wonder R1 gets hot.

    The 23 V reading 27 V is imho not an issue either as this is the source of other regulated voltages and as these read o.k., as you state, power seems to be good. The issue with the missing sound is located elsewhere I would think.
     
    shrtrnd likes this.
  5. Jimbert

    Jimbert

    11
    2
    Dec 2, 2014
    Bertus, Harold,
    I also think the "No Sound" problem must be downstream. However, The 200 deg F is certainly not normal. The thermometer sensing area seems to be pretty localized as I move it around the high temp resistor. That's still a mystery. And as I said all voltages are correct (except the 23V reads 27V) including the 53V. The 53V feeds 3 separate power amps whose component temps seem normal. I've included below the description of the power supply from the manual. Perhaps it will help. It just seems like the "No Sound" problem would be associated with a central supply. Thanks so much for any help. My electronic knowledge is pretty superficial.
    Jim B
    Organ power supply4_0001.jpg
     
  6. bertus

    bertus Moderator

    1,479
    584
    Nov 8, 2019
    Hello,

    The +23 Volts is unregulated.
    Is the -23 Volts unregulated correct?
    It is made from the same taps of the transformer.

    Bertus
     
  7. Jimbert

    Jimbert

    11
    2
    Dec 2, 2014
    Bertus,
    According to the schematic the 23 V both + and- is unregulated. I measured both again and the +23V tap measures +25V and the -23V tap measures -28V. Not sure what that means, if anything.
    Jim
     
  8. bertus

    bertus Moderator

    1,479
    584
    Nov 8, 2019
    Hello,

    On an unregulated powersupply, the voltage may vary with the load.
    The +23 has larger capacitors, as the likely expect a higher load.
    The voltage may well be correct.
    The regulated voltages shoeld not vary with the load.

    Bertus
     
  9. Jimbert

    Jimbert

    11
    2
    Dec 2, 2014
    Bertus,
    Thanks for your reply. Do you see anything in the power supply that would explain the "No Sound"? I will try to isolate the power amps to see if there's any effect.
    Jim
     
  10. TallPaul

    TallPaul

    11
    4
    Oct 5, 2014
    Maybe a transistor opened up. I would replace all those dried out electrolytics. test the diodes
     
  11. WHONOES

    WHONOES

    1,099
    309
    May 20, 2017
    I would imagine that if the power supplies are as your documentation dictate then the problem is with one or both of your power amps'.
     
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