Question about Pyramid - PS21KX 20 Amp Power Supply Car Audio Amplifier

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Hello, I have a pyramid power supply(PS-52KX), that recently started with a overvoltage problem. I run a Galaxy DX94 HP 10 meter transceiver, and just recently, when I key up the radio, the voltage goes from where I set it(around 14.5 VDC), to wide open voltage. I have recently replaced the TIP41C transistor, and the NTE 5554 Transistor (crossed referanced part number), on the small output board, that goes to the power posts. Still the problem remains. I'm not sure where to go from here. Any help would be greatly appreciated. I don't mind removing and replacing compounents. I just can't have my ham radios on and overvoltaged power supply. Thank You. Best Regards, Chris ---------------

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  • 631 Answers

I'm not sure what you mean by 'wide open voltage'. If it's over 17v, the supply may have multiple problems. I don't have the 52kx schematic but other Pyramid supplies have over-voltage protection. There is an SCR that is triggered when the voltage gets to ~17v. This should clamp the output and trigger a shutdown. You should check the 16v Zener diode and the SCR. If the SCR or the Zener is defective, that would prevent the over-voltage from clamping the voltage. Also confirm that the SCR has a solid connection to the ground terminal of the supply. If it's open, that could prevent the clamp from shutting down the supply.

If the voltage is going high, measure the DC voltage from pin 4 to pin 5 of the LM723. It should remain the same at all times. Also measure the voltage from pin 5 to the ground terminal of the supply. That should also remain constant at all times.

Posted on Aug 20, 2008

  • Wayne Feierabend
    Wayne Feierabend Jan 12, 2017

    What is the value of Z1? Can't read/test mine cracked. Same unit PS52KX. What diode do I order?

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