Pyramid PS-26KX power suply

[Mrbadness]

Hello I have a power supply thats not working. The needle jumps from 6 volts up to 15 back and forth. I put a load on it and it stays at 6 volts. The relay clicks when it jumps. I don't know where to start trouble shooting. Can anyone help??

[CapLeaker]

Re: Pyramid PS-26KX power suply

These Pyramid PSU’s really suck balls. Is the fan still working? What does the amp meter say? Can you put a small load on it like some car headlight bulb? Sounds like a regulation problem of some sort. Is the regulator LM723 IC in a socket? Remove it and put it back in.
Check the 12V regulator (7812) and it’s capacitors, as it supplies the voltage to the relay and other IC’s. There is a 16V zener diode, that makes the SCR fire. Download the manual, the schematic is in it.

Usually with these linear PSU’s the fan fails (pass transistors get too hot), pass transistors fail because the heat or some other unfortunate event (mounted on a large heat sink), the regulator IC LM723 and a bad SCR. The TIP41 rarely goes bad. I’ve seen bad meters on them too, but that is besides the point.

[redwire]

Re: Pyramid PS-26KX power suply

Pyramid Power Supply schematics here: http://www.repeater-builder.com/pyra...mid-index.html
The common problems are failed pass-transistors. I would see why the output voltage is too high at no load- it might be a damaged pass-transistor. If the output goes way too high over ~17V the SCR crowbar trips which should blow the fuse.

If the power supply collapses, i.e. output voltage does not keep up to the setpoint, it activates the protect buzzer and LED.
The transformer tap-change relay activates when output is above some voltage so this is normal that it is clicking.

[Mrbadness]

Re: Pyramid PS-26KX power suply

Okay that gives me a place to start. Thanks for the input. anyone out there have one of these??