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cant get 5k pot adjustment to work. what am i doing wrong? does R2 hook into Adj?

This is a schematic of the Power Supply

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hillbillyboy_316 (author) 7 years ago
replaced the lm338k with a lm317t and im getting 1.2volts to 32 volts.  must have had a bad voltage regulator?
hillbillyboy_316 (author) 7 years ago
im not getting the 1.25 reference volts from my regulator  im only getting .50 volts
hillbillyboy_316 (author) 7 years ago
have a 5k pot and 240 ohm resistor and i have no load on it
hillbillyboy_316 (author) 7 years ago
built it on veroboard and one of the copper tracks had a small whisker still attached between input and output of the regulator.  but i can only get adjusted up to 9.4 volts
hillbillyboy_316 (author) 7 years ago
figured out my problem but can only get up to 9.4 volts
hillbillyboy_316 (author) 7 years ago
what about redesigning schematic for a lm317 instead of 338k?
hillbillyboy_316 (author) 7 years ago
did that and i didnt have a 1/2 watt 120 ohm resistor so i used a 1/4 watt and turned i had a little flame come off that one when it burnt up
Substitutions
C1 1 14000uF or 10000uf 40 VDC Electrolytic Capacitor  
C2 1 100uF 50Vdc Electrolytic Capacitor  
C3 1 0.1uF Disc Capacitor  
C4 1 0.01uF Disc Capacitor  
R1 1 5K Pot  
R2 1 240 Ohm 1/4 W Resistor  
U1 1 LM338K 1.2 to 30 Volt 5 Amp Regulator  
BR1 1 10 Amp 50 PIV Bridge Rectifier  
T1 1 24 V 5 Amp Transformer  
S1 1 SPST Toggle Switch  
MISC 1 Wire, Line Cord, Case, Binding Posts (for output)  
here is the values for the components.  someone told me that the schematic is wrong and the resistor needs to be 120 ohms and the 5k pot needs to be 2.5k.  would that solve my problem?
hillbillyboy_316 (author) 7 years ago
use 1 1k resistor or one for C3 and one for C4?
hillbillyboy_316 (author) 7 years ago
yes i checked the wiring for the 338k, looks right to me.  as far as the caps, take all 3 out or just C3 and C4? the data sheet says a 120 ohm resistor from out to ADJ for the regulator
hillbillyboy_316 (author) 7 years ago
had a bad 5k pot replaced it and now when i turn the power supply on the 240 ohm resister starts to get hot and burns up
hillbillyboy_316 (author) 7 years ago
C3 and C4 are disc capacitors and arent polarized.  i checked everything and it seems everything is correct. when i turn it on it goes straight to 33 volts.  could my 5k pot or my voltage regulator shorted and went bad.  schematic called for 24v 5 amp transformer and i used a 6 amp.  and the C1 was supposed to be 14000 uf and i used 28000 uf. everything else is the same values. is there anyway to check 5k pot and voltage regulator to see if they are good?
hillbillyboy_316 (author) 7 years ago

R2 is supposed to be 240 ohms but every time i hook one up it burns it up

supply1.gif
It can't "burn up", so its not wired correctly I'm afraid.

Steve
lm338k regulator
AndyGadget7 years ago
Your circuit looks OK, straight off the datasheet.
I'd suspect a wiring error - A short circuit somewhere?
Very easy to miss a wire whisker or track which isn't quite cut through.
Also, if your regulator is on a heatsink, make sure the two pins aren't touching the sides, and check the case (output) isn't grounded anywhere. 
Re-design7 years ago
If you're trying to build and instructable, post the the comments to that page.  We don't have any idea what your circuit is and the author of the instr.  may never se it here.
LM317 ?
mathews7 years ago
When you say R2, what do you mean? If you can post a circuit diagram, and details of the Pot, then we can help you better.

If you are sure you have put the pot in the right place in your circuit, are you using the right pins? i.e the wiper pin and an outer pin (correct), or both outer pins (giving a fixed 5k resistor).