Adjustable dc power is not working on pcb

[jhorapalok]

I have made two variable dc power supply using LM 317. I made them on vero board and stripboard and both of them working perfectly.
Then i wanted to make them on pcb. I drew the schemetic on the copper side with the help of a marker pen (mirrored schemetic ofcourse!) and then etched the pcb by ferric chloride. PCB is ok but after connecting the parts the power supply is not varying. it is giving the highest output voltage. I checked and rechecked the circuit, everything seems to be ok but the power supply is not working. what is the problem? please help.

 

[dougy83]

check for a connection from the ADJ pin to your potentiometer (pot) and from your pot to ground (0V). Also check that your pot has the appropriate resistance.

There could also be an error in the footprint pinout of the LM317, so if you can provide images of your schematic and PCB someone may be able to check them for you.

 

[KeepItSimpleStupid]

What does your schematic look like? Since you probably just joined it might take a while before you can post schematics and even links.

What will help is the voltages at Vin, Vout and adj relative to ground and the voltages across the divider resistors.

If you used the diode that is between Vin and Vout, the diode can be installed backwards.

The schematic should be simple enough that we could spot the errors, if you posted bit sides of the PCB. You can use go advanced/manage attachments to upload attachments.
One other possibility, is the lack of a load. Load the output with at least 20 mA.

If you used a potentiometer, make sure the resistance varies as expected. Confirm the resistor values with in-circuit, powered off resistance measurements.

 

[dr pepper]

Maybe you connected the trimpot accross the track rather than one end of the track and the wiper, this has got me before esp when it isnt clear which is which.

 

[jhorapalok]

I think i have messed up connecting the transformer. I tried to use a transformer that labeled 9V x 2. It has two wires at its primary side and three wires at secondary side. Wire 1 and 2 of the secondary side read 10v ac and wire 3 and 2 also read the same. I wanted to get 18 volt for my power supply and so i connected wire 1 and 3 of the secondary side to the two ~ pins of a bridge rectifier leaving wire 2 unused.
Then i connected + of the bridge rectifier to the positive side and - of the bridge rectifier to the negative side of my circuit. Is there anything wrong in this connection?

 

[KeepItSimpleStupid]

There is nothing in theory that is wrong with what you did, however 9 V x 2 would usually mean that there would be 4 wires at the secondary.

Two windings at 9VAC or 4 wires. This would mean that you would get either 0 or 18 VAC wen the windings are placed in series depending on the phase.

With a full wave bridge and 18 VAC in, you should be getting close to 25 VDC.

So, what do you get between 1 & 3?

And what do you get at the output of the bridge?

A possibility is that the transfomer is bad, thus you read a good open circuit voltage, but once you put a load on it, one or both of the windings or even the primary nearly opens.


The other marking would be 18 VAC CT. for 3 wires.