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  1. gerryt

    Switching Power Supply Short

    The resistor's resistance value is supposed to be 100K and it is 1 milli ohm. I have also found two MOSFETs that were not working when tested on the multimeter.
  2. gerryt

    Switching Power Supply Short

    Thanks for your words of wisdom. Checking each piece one at a time, so far have found a faulty resistor.
  3. gerryt

    Switching Power Supply Short

    Hi all, I am trying to find a short in a SMPS for a subwoofer. It keeps blowing fuses as soon as the 120 AC power is turned on. The NTC Thermistor was damaged when I took a look at the board. Any suggestions as to what the most likely cause of this is?
  4. gerryt

    Carvin LM15 Powered PA Cabinet Protect Circuit

    Yesterday when I was doing some testing on this unit, it was unplugged but I got a mild shock when touching the large heat sink and fan assembly. The filter caps were still holding some current. But I am wondering why the heat sink would be transmitting some current. I have uploaded a...
  5. gerryt

    Carvin LM15 Powered PA Cabinet Protect Circuit

    Thanks for your reply. The unit has XLR output for another powered unit, but does not allow for unpowered speakers to be added. I disconnected the speakers and the protect circuit still is on. I will check the output transistors.
  6. gerryt

    Carvin LM15 Powered PA Cabinet Protect Circuit

    I have a Carvin LM15 powered PA cabinet where the protect circuit light stays on when the unit is powered up. I have tested the woofer and tweeter to be sure they are working and have continuity. I have not been able to find a schematic for this unit and have contacted Carvin to see if they can...
  7. gerryt

    Solid State Bass Amp hums

    The hum is present even with all control levels turned to minimum. It does not change if the controls are turned up.
  8. gerryt

    Solid State Bass Amp hums

    Hum is present even when no instruments or CD are plugged in. Input cables are shielded. I am using a bass that does not hum when played through my other bass amplifiers. I have noticed after listening more carefully that the humming sound comes mostly rom the amplifier itself more than...
  9. gerryt

    Solid State Bass Amp hums

    Everyone helped me so much to solve the overheating problem I had with my QSC Amp, so I thought I would ask for help again with another amplifier problem. I have a small Ampeg BA - 108 (first generation) solid state bass amp that hums continually and also presents a very small amount of...
  10. gerryt

    QSC Power Amp gets hot

    I am not really sure why the channel was so hot. I had the amp in my portable rack since I bought it used a few years back, so I don't know if it has been running hot the whole time I have had it. I took it out of my rack to put in to my studio to power my mid field monitors and that is when I...
  11. gerryt

    QSC Power Amp gets hot

    I adjusted the trim pot a very small amount, from about 10 o'clock to 11 o'clock. I will monitor the amps performance in my recording studio, I use it to power my mid field monitors. Amazing how a very small adjustment can make such a difference.
  12. gerryt

    QSC Power Amp gets hot

    I have adjusted the bias trim pot for the channel that was getting hot and the problem seems to be resolved. Hopefully this will continue. Thanks to everyone for your help with this.
  13. gerryt

    QSC Power Amp gets hot

    Thank you very much for your suggestions, I will check the bias trimpot and the NTC.
  14. gerryt

    QSC Power Amp gets hot

    Thank you so very much for helping me with this, I really appreciate it. I will try reducing the trim in channel two and see what happens. I just tried this and channel two still gets hot. I could only turn the wiper a small amount and it was at the end of its travel. I have also noticed...
  15. gerryt

    QSC Power Amp gets hot

    No, it is the other channel
  16. gerryt

    QSC Power Amp gets hot

    You are correct in identifying the thermistor attached to the heat sink. I tested it by adding heat from a soldering iron using my multimeter to see if impedance increased as the thermistor warmed up. The resistance increased as it warmed up. I also checked to be sure it was well connected...
  17. gerryt

    QSC Power Amp gets hot

    Hope I did this right for you , base pin to emitter pin in quiessent mode: Channel one: .706 DCV and -.645 DCV Channel two: .864 DCV and -.580 DCV I did notice that the numbers for all four power transistors decreased slowly as I held the multimeter leads on the pins.
  18. gerryt

    QSC Power Amp gets hot

    Voltage for power transistors in quiessent state: Channel one -34.00 and +34.00 DCV Channel two -33.00 and +32.00 DCV (this is the channel that gets very hot) DC Voltage for amplifier output in quiessent state: Channel 1 -1.2 DCmV Channel 2 1.0 DCmV
  19. gerryt

    QSC Power Amp gets hot

    Ok, figured how to test the + and -37V DC rails. They are both running at -35 and +35 DCV
  20. gerryt

    QSC Power Amp gets hot

    Please bear with me, I am just learning about how to do this. I have found the ground rails on my circuit board, but I do not know where to put the leads from my voltage meter.
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