Hello , Am wondering if anybody can help me please. I have been looking for a (ideally) AC/DC variable power supply but not too expensive ,
Ideally for 0 volts to about 35 volts after looking around my head was spinning with all the different types but i stumbled across a DC 0-30 volt kit to build (which looks straight forward to build) on ebay
http://www.ebay.co.uk/itm/Regulated...V-2mA-3A-Precision-Variable-Lab-/132104143924
so with it been cheap and thought it i would get me half way to my goal ..
Problem i have is that after i assembled it, and checked it , its not working , i got 20 vac going in (it does say 24 vac tho but would this matter?) at the fan i get 24 volt but the output not power at all . could anyone give me any advice other that putting it in the bin . i have been i touch wit the seller but they don't know anything about electronics they just sell them (am guessing they buy them in from china or Hong Kong) they asked me to take it to a specialist to see if they can sort it , i will be getting back to them if i cant get it working to get a refund i just thought i would see if anyone has any experience with this type of power supply first .
Cheers Mal

 

Did it come with a circuit schematic that you can post here?

 

Can you take notes of the chip numbers and large transistor, it looks like they are op amps, can be easily re traced.?

 

Do you have a schematic?

Using 20VAC instead of 24VAC, would reduce maximum output voltage by 4*1.414 volts.

 

Did it come with a circuit schematic that you can post here?

Hello Mr Chips . No it did not come with any schematic's it was just a printed circuit board with just the right amount of components . i will take picture of the circuit and i will give the numbers on chips and transistor ASAP cheers Mal

 

i will take picture of the circuit and i will give the numbers on chips and transistor

We could see them marked on the blank board. A 7824, several TL081's, and a power transistor.

What we need is a schematic.

 

the chips are all the same TLO81CP the large transistor D1047
Here is some pictures i know there is no heat sink but i wanted the circuit working before i fitted them i was going to also fit a cooling fan too .

 

Take photo of the pcb track side also,..

 

Have a look at the picture of it on the advert ( hover mouse over pic to enlarge) then very carefully check that all the components are fitted exactly the same, (colour codes, polarities etc) I built a kit of an audio bargraph indicator for an amplifier and the assembly instructions had several mistakes.

 

hello i have just been doing some digging about on the net for schematics for this circuit, I found this video on you tube showing someone assembling a kit and if you fast forward to about 17 minutes he puts up a schematic of his circuit . The circuit board and components look exactly the same as the one i have apart from the small diodes (4148 , 5v1) are shown printed the opposite way round ? the tracks on the circuit boards are exactly the same as i see ?? and the guy in the was using 24vdc so his didn't work first time , i am using 20vac cheers Mal

 

Perhaps cloned from this:

http://www.electronics-lab.com/project/0-30v-laboratory-power-supply/

 

I've seen that circuit described somewhere else, I think I had googled images for variable power supplies and it was one of them so maybe you could find it and see if there are any comments or differences.

 

Perhaps cloned from this:

http://www.electronics-lab.com/project/0-30v-laboratory-power-supply/

Ah yes Mrchips, the very one I had seen

 

So what voltages are you getting across C2,C3, Pins 4,7 of the op amps from ground?

 

So what voltages are you getting across C2,C3, Pins 4,7 of the op amps from ground?

Hiya Dodgydave,
C2 is 3.6v C3 1.8v pins 7 are 16.4v and pins 4 are 1.3v

 

Hiya Dodgydave,
C2 is 3.6v C3 1.8v pins 7 are 16.4v and pins 4 are 1.3v

There's your problem then, you haven't got the Negative voltage on C3 of 5.6V, C2 should be at least 15V.

 

There's your problem then, you haven't got the Negative voltage on C3 of 5.6V, C2 should be at least 15V.

cheers i think i would be better getting the correct input power supply then check it again i have checked the diodes which seen to be ok . Do you reckon changing the power supply will solve it ??

 

cheers i think i would be better getting the correct input power supply then check it again i have checked the diodes which seen to be ok . Do you reckon changing the power supply will solve it ??

You need to check the power supplies first, Ac in, Dc across the capacitors C1,C2,C3, check polarity of the diodes D1,2,3,4,5,6,7

 

You need to check the power supplies first, Ac in, Dc across the capacitors C1,C2,C3, check polarity of the diodes D1,2,3,4,5,6,7

Thank you i will check them tomorrow . I do know that's its only 20vac input tho ...

 

You need to check the power supplies first, Ac in, Dc across the capacitors C1,C2,C3, check polarity of the diodes D1,2,3,4,5,6,7

Hiya Dodgydave , Sorry it taken a while but i had computer problem so couldn't get back to you with the out come .
The polarity on all diodes are correct as the printed circuit board indicates, and the ac power in is 20vac . The DC power across C1 is 5v ,C2 9.2v and C3 25v.
This is very frustrating as i have got over everything three times and checked all joints and all seems ok .
Any help will be much appreciated Thank you .Mal