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

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PS36K power supply overload problem

I have a PS-36K Pyramid poewr supply. When I turn it on it goes to 15 volts and the protection light comes on and the unit beeps. I cannot adjust voltage. I need a schematic and would appreciate any suggestions you can give. THANKS!

Jim Goldring

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Re: PS36K power supply overload problem

Most of Pyramid's supplies are based on the LM723 voltage regulator. The DATASHEET should tell you most of what you'll need to know to repair it. THIS is the schematic diagram.

If the output voltage drives the voltmeter to the end of the scale, it likely has one or more shorted power transistors.

Posted on Dec 21, 2007

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The protect light is a notification that the amplifier has reached a set temperature and shuts the amp down till it cools off. Look for the thermosister on the heatsink and follow the circuitry back to the control chip. Once you get that fixed the amp should power up until it gets too hot and the protect circuit kicks in. I had one of these amps for a while and the circuit was very touchy. Regards, rcampsr

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Generally, the fuse only blows when the rectifiers fail. In other Pyramid supplies, they use a square, 4 terminal bridge rectifier. They probably use the same thing in your supply.

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1 Answer

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...

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.

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Have you done any troubleshooting at this point?

Are you going to try to repair this yourself?

Have you tried to locate a schematic for the supply?

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PB1500 no diag. lights - Power - OK

I don't know how you checked the fuses but if you didn't use an ohm meter, you need to confirm that you have B+ and remote at the amplifier.

With your multimeter set to DC volts, the black meter lead on the ground terminal of the amp and the head unit on (so the amp will have remote voltage applied), touch the red lead alternately to the B+ and remote terminals of the amp. If the voltage is below ~11 volts, you need to check the wiring feeding whichever line is too low.

If the voltage is sufficient at the remote and B+ terminals, the switching power supply has probably failed in the amplifier.

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