Pyramid PS-26KX Benchtop Power Supply Problems

[coppercitycomputer]

Greetings! My boss gave me a Pyramid PS-26KX bench-top power supply to repair. It's 6-15VDC at 25AMP. The problem is the protection light flash's and it chirps over and over again. The AMP meter also max's out. It has four large 2N3772's on the back heat sink. I did some investigating and three of the large transistors get pretty hot quickly in the matter of a few secs, also something labeled TYN416 gets "smoking" hot at the same time, the center leg of that part is discolored. I also found one of the wires that go's to one of the 2N3772's disconnected, I can not be sure it did not brake lose with me fiddling around in there!

http://www.manualslib.com/manual/312...id-Ps26kx.html

How do I test the parts? Thanks for your help!

[stj]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

z1 and the scr form a crowbar circuit that will shortcircuit the supply if the output goes over 16v

i suspect either it's screwed or the output IS over 16v.

so, disable the crowbar by removing the scr and see if it runs - if it does then meter the output voltage.
AND DONT LEAN OVER IT INCASE C7 EXPLODES!
it's under-rated and should be 25v

if the voltage looks good and goes up and down as it should, either the scr is shorted or zd1 is fucked.

if you have over 16v then we will look more closely at it.
before you do any of this,
make sure none of those 2n3055's are shorted, that would have the same effect.

once it's fixed you should upgrade c6 & c7 to 25v btw.

[budm]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

What resistance do you get when measure at the output terminal and the Ground terminal (power not applied of course)?

[coppercitycomputer]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

Bud M, I get about 640 set on the continuity setting on my meter, between the pos and neg outputs on the front of the supply.

STJ, I am sorry but I did not understand a thing you said besides make sure none of the 2n3055's are shorted. How do I check or test them? My knowledge is pretty limited.

[stj]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

shit, i assumed you were an engineer!

o.k. do a continuity test on the 2n3055's
between the case and each pin.

[coppercitycomputer]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

STJ, They all check constantly expect the one that does not get warm. The last one on the left, I get about 500 on the blue wire and about 18 on yellow wire expect on the last one the blue is about 1500. I was testing to the red wire, doing the case got me nothing on any of them.

[budm]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

The 2n3055 are connected in parallel (Collectors are tied together, Emitters are tied together), so the RED wires are connected to the Collector (case), the Blue wires look like for the Emitter which also tied together.
I expect then that the reading between any RED and Blue will have the same reading. Also it looks like one of the Yellow wire is not solder to the pin of the 2n3055 (2nd from the left)?
Transistor pin out:
http://www.ese.upenn.edu/detkin/comp...ransistors.htm
Can we also get good pictures of the control board?

[coppercitycomputer]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

Budm, you are correct, the readings between any RED and BLUE are the same. That wire was disconnected when I removed the heat sink off the back, but I can not be sure it was like that when I got it or I knocked lose taking it apart.

[budm]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

That may explain why it did not get hot, that is the Base of the transistor. And if that wire touched the red, the 2N3055 will be fully on. If Q1 (TIP41) is shorted or leaky, that will also turns on the 2N3055 without regulation.
So the reading on Red and Blue is?
Check and resolder the wires the transistors and check the wires and solder joints on the controller board and over all wires connections in the unit, then power up again real fast to see what happen.
BTW, did you hear the Buzzer or the relay clicks?

[coppercitycomputer]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

Budm, I will have to drag out my soldering iron, to do that. The reading is about 1200 on red to blue. The one that did not get warm has all it's wires connected (far left) 2nd from the left is the one missing a connection. No relay clicks just chirping from the little beeper. and the protection light flash's each time it chirps.

[budm]

Re: Pyramid PS-26KX Benchtop Power Supply Problems

So the 2n3055 are not shorted out. They may be driven full on by Q1 or the regulator IC1 (LM723?) has the problem.