Pyramid PS52-KX trouble going to 24 volts??

[bigmann3104]

I have a Pyramid PS52-KX Power Supply and I have my radio hooked up to it and one day I was just sitting there and my radio lights just went bright and I noticed that the power supply volt meter went all the way to the right past 20 volts! I tested the power supply postd with my fluke volt meter and I get 24 Volts at the power posts!!

Does anyone know what went bad in the power supply that is making it go to 24 volt? And what to replace to get it back to 12 to 15 volt??

Thanks!!

 

[Robb]

Sounds like it lost the regulator.

 

[bigmann3104]

there is a small board inside the power supply and there is a regulator in there. It is a TIP-41C but there is also another chip in there that is a TYN688 I dont know what this one is but on the solder side of this 3 leg chip between the middle leg and the red power wire going to the post terminals the trace is burnt!! So I dont know if this Tyn688 is bad or what? I fixed the trace that was burnt between the middle laeg if the TYN688 and the red supply wire and it still is givving 24 Volts!!

 

[Robb]

Probably both devices are toast.

That is to say, the regulator TIP and the controller IC are prolly toast.
I would replace them both. Do the TIP first; but it may be more than that. When these supplies get clogged up/choked with 'dust bunnies'; they start self-destructing. Keep them cleaned out and well ventilated. I worked on one of those before for a friend and had to replace a bunch of stuff because he allowed it to get chuck full of dust, overdrive it with a linear, and ran it hot for days on end that way.

 

[bigmann3104]

The inside of this power supply is so clean it looks brand new!! but anyhow ill replace the TIP because I have those and we will see what happens!! but I dont know where to get the TYN688 or a part that would work to take its place as a drop in replacement

 

[bigmann3104]

Ok Changed the TIP and i still have 24 Volt!! I need to look else where maybe the LM732???

 

[Robb]

Just start testing all of the parts in that circuit. If you cannot test the IC; replace it. Also start testing the pass regulator transistors. It's gonna get ugly before it gets right. Like I said; I ended up replacing more that a few parts. Also check the bridge rectifiers first. Be especially CAREFUL around the filter caps; discharge them!

 

[unit_399]

Check the output pass transistors. Probably one or more is shorted emitter to collector.