Odd output from Elenco XP-15K Power Supply - Schematic

[tomherrick]

Schematic of XP-15K.

[tpowell1830]

Hi Tom, you can find your original post by going to the menu above and clicking Profile and then Show Posts. This belongs with your original post.

[rstofer]

Right, add the schematic as an attachment to the other post and then delete this post (if possible).
It's kind of a PITA to flip between two threads to try to follow the schematic versus the PCB images.

[rstofer]

Diodes D5 and D6 make up a poor man's zener diode and the voltage between ground and the point where the diode connects to R4 should read -1.4, give or take.  Black wire of you meter goes on ground.  This negative voltage is what allows the regulator to get down to 0V.

I don't know the AC voltage between the blue and yellow wires of the transformer but about 1.4 times that value should be measured at pin 3 of the LM317 as a DC voltage.

Pin 1 of the LM317 should move between some negative value, like -1.4V, up to some positive value, nearly 15V,  but I haven't calculated the exact range.

[Simon]

Please refer to: https://www.eevblog.com/forum/beginners/odd-output-from-elenco-xp-15k-power-supply/
Tomherrik, this forum does not work like this, you need to post in the original topic or you will just have a bunch of unrelated and unintelligible posts floating around that no one can decipher. You can also edit your post if you want to add information.