adding lm317 supply to existing -15/+15v PSU - running into issues

[Humner]

I have an existing -15/+15 power supply for a project I'm using based on 7815 and 7915 IC's. Its using a transformer with 15-0-15 secondaries to power this.

the -15/+15 power supply has been working well without issues and I now want to add an adjustable LM317 based PSU to this existing setup.

For the LM317 supply, its based mostly off this(only difference is 270 for R1)

http://circuit-zone.com/ediy_blog/675/1.5v-30v-1.5a-lm317-variable-power-supply.gif

I'm using the existing diode bridge and taking voltage from the positive side to the IN leg of the LM317 and then the ground is connected to the existing ground.

I turned it on, and managed to burn out the adjustment POT only when it was turned to least resistance. I then went to check for shorts/solder bridges etc and it looks OK. I triple checked the LM317 pinout as well(as I know its different to 7815 etc) and confirmed this is OK as well.

So now I'm hoping to check that I have actually wired this up correctly to the existing PSU before I burn out another POT  ;D

 

[Humner]

I think I may have found something that might cause some issue.  :

I've actually got R1 as 72ohms. I added in another resistor in parallel when I needed to add it in as series. Silly mistake

Anyway - would this cause the expected POT burn out?

 

[Humner]

I found the problem...

turns out I had one of the protection diodes the wrong way,  the one going from output the adjustment leg.

feel a bit sheepish.  :-X

 

[gyraf]

+1 for trying and finding by yourself!