dc POWER SUPPLY PROBLEM

Hi all of them
i am facing a problem now a days
problem is that i had bought a power supply from market, and it makes PROBLEM from the FIRST day i had bought this
well PROBLEM is that, when i Swith ON the supply, display(DIGITAL VOLTMETER) works, but showing 0000 VALUES
when i vary from KNOBS, then nothing is going to happen
i open the POWER SUPPLY, and check fro the whole circuit that might be, if any thing burnt in it, then i must reploace, but every thing is OK from INSIDE
i study this supply since last week but uinable to LOCATE the EXAXT FAULT
if any one of you have any IDEA about this FAULT then must told me
i also mention that, i CHECK VOLTAGE from DIGITAL MULTIMETER at different part of power supply, it SHOWS (20V DC) which mean that transformer is OK....
so plz help me about this issue
waiting
TAYYAB
ELECTRICAL ENGINEERING STUDENT

Very frustrating to buy a supply that doesn't work.

It can be difficult to figure out what's wrong with a circuit without a schematic diagram. And lots of instruments these days have a lot of digital functionality on one chip; the schematic can be useless unless you also have the firmware source code.

If there's nothing obviously wrong with the components, the best strategy would be to return it to the vendor under warranty, if that's possible.

Check if the the output voltage varies when you rotate the knobs.

Like I said on the other website, it is Made In China.
Don't buy no-name-brand cheap junk.

Audioguru said:

Like I said on the other website, it is Made In China.
Don't buy no-name-brand cheap junk.

Click to expand...

Well said.

If it is anything like the cheap electronic junk toys that my kids get all the time, pull lightly at some of the wires, they may come right off. I can't tell you how many toys I have opened up after one day that quit working.

Little fuse somewhere? A panel fuse or circuit breaker on the back of the unit? Or a fusible resistor on a PCB somewhere, looks like a resistor with a low value written on (often less than 1 ohm) and rough matte paint, not shiny. They blow open circuit.

And check all the solder joints with a good magnifier.