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

This is a schematic of the Power Supply

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hillbillyboy_316

8 years ago

replaced the lm338k with a lm317t and im getting 1.2volts to 32 volts.  must have had a bad voltage regulator?

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hillbillyboy_316

8 years ago

im not getting the 1.25 reference volts from my regulator  im only getting .50 volts

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hillbillyboy_316

8 years ago

have a 5k pot and 240 ohm resistor and i have no load on it

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hillbillyboy_316

8 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

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hillbillyboy_316

8 years ago

figured out my problem but can only get up to 9.4 volts

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hillbillyboy_316

8 years ago

what about redesigning schematic for a lm317 instead of 338k?

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hillbillyboy_316

8 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
C1114000uF or 10000uf 40 VDC Electrolytic Capacitor 
C21100uF 50Vdc Electrolytic Capacitor 
C310.1uF Disc Capacitor 
C410.01uF Disc Capacitor 
R115K Pot 
R21240 Ohm 1/4 W Resistor 
U11LM338K 1.2 to 30 Volt 5 Amp Regulator 
BR1110 Amp 50 PIV Bridge Rectifier 
T1124 V 5 Amp Transformer 
S11SPST Toggle Switch 
MISC1Wire, 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?
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hillbillyboy_316

8 years ago

use 1 1k resistor or one for C3 and one for C4?

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hillbillyboy_316

8 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

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hillbillyboy_316

8 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

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hillbillyboy_316

8 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?

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hillbillyboy_316

8 years ago

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

supply1.gif
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AndyGadget

8 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. 

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Re-design

8 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.

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mathews

8 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).