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I bought this adjustable power supply kit and successfully assembled it. I wanted to upgrade the potentiometers to 10 turns so I could have fine control over the current and voltage limits set. Both potentiometers are 10K ohm and I have tested both to make sure they were in that range. For some reason, the output of the board drops somewhere like -0.5V when I try to use the upgraded potentiometers but works fine with the originals. What is causing this?

These are similar to the originals, only without the rear two pins (all i could find)

These are the upgraded potentiometers

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  • \$\begingroup\$ User error - incorrect wiring, damaged PCB when desoldering the original pot, etc. I don't think anyone will be able to answer this without more details like photos. \$\endgroup\$
    – pipe
    Commented Feb 27, 2016 at 4:55

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I'll make a WAG on this- the wiper is typically the rear terminal in 10-turn helical pots (vs the middle terminal on single-turn pots), so if you wired the middle terminal to where the wiper should go it wouldn't work well.

Note that Bourns numbers the terminals 2-1-3 from the back (see the drawing).

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    \$\begingroup\$ Yeah that was it. I guess i know now for the future to check BOTH terminals in reference to what i believe is the wiper. Much appreciated! \$\endgroup\$
    – Daniel
    Commented Feb 27, 2016 at 5:24
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    \$\begingroup\$ It's not a bad idea to play with the original potentiometers and the new ones with a multimeter set to Ohms mode; by doing this you can easily discover which two nodes are the terminals of the main resistive element, and which is the wiper. \$\endgroup\$
    – Kaz
    Commented Feb 27, 2016 at 7:28
  • \$\begingroup\$ As @Kaz says, btw you were lucky the pot was not destroyed- if it's connected as a voltage divider and you turn the wiper to minimum resistance the expensive pot can be fried. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Feb 27, 2016 at 13:25

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