Chinese power supply troubleshooting : probleme to ask for...

Thread Starter

AhmedKhouaja

Joined Nov 2, 2019
9
Hi guys !
First i'm new member here with you , and i hope you guys help me with my power supply kit problem:
Like most people , i have problem with this kit wich is i get -0.45v when the V and A pot are fully anti-clockwise and i get only 5.1V when the V and A are fully clockwise.
I checked almost the whole circuit with the help of schematic that is made by "Netzener" .
I'm using 12-0-12 , 3A transformer...
So guys can you guess where is the probleme? I will attach a pdf file wich can help you understant the whole circuit...
Thank you .
 

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bwilliams60

Joined Nov 18, 2012
1,199
Well the first thing that pops out at me is that they are telling you to use a 24V transformer. Can you post pictures of your board front and back, nice and clear. There are also reference points that you can measure from to narrow down the problem area. I would suggest maybe reading through the manual and you will find a lot of good information to help you out.
 

Thread Starter

AhmedKhouaja

Joined Nov 2, 2019
9
Of caurse , i will attach 2 pictures .
The probleme is as the pdf attached in the first commant , i need to find 10V between (Vout-) and R12 , but i get only the half of it , i find 5.1V !
The other test are right as the pdf telling , and for the transformer its not neccessary 0-24V because its linear power supply and 1V for each transistor will activate it (as i thought). Webp.net-resizeimage.pngWebp.net-resizeimage-2.jpg
 

Thread Starter

AhmedKhouaja

Joined Nov 2, 2019
9
I did all the mesurment, and they are all right, except one i will show you where is the error ...
And for the transformer , i'm using 0-24V AC and i'm getting the -5.5V as expect...
Screenshot_20191103-162436_Drive.jpgThe point that shows 11.4V , for my case i get only 5.1V the half of its real value ! ....
 

DickCappels

Joined Aug 21, 2008
5,928
The output is 30.1V even though the base of Q2 (Vset) is only 5.2V

There appears to be something wrong with Q2-Q4, something like a emitter-collector short in one or both of these transistors.

Edit: Originally referred to "Q2-Q2" as "Q1-Q2".
 
Last edited:

Thread Starter

AhmedKhouaja

Joined Nov 2, 2019
9
The output is 30.1V even though the base of Q2 (Vset) is only 5.2V

There appears to be something wrong with Q2-Q4, something like a emitter-collector short in one or both of these transistors.

Edit: Originally referred to "Q2-Q2" as "Q1-Q2".
Like you said sir, maybe these two transistors are faulty, i will replace them, also i will replace the U2 with new TL081 too and i'll post the new results....
 

Thread Starter

AhmedKhouaja

Joined Nov 2, 2019
9
Finally guys, i just made it , i fixed it.
The problem was with the U2 :TL081
The output of this IC was giving only 6V as maximum output...
Thank you guys for your replys , it really helps me ...
 
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