I have a 5 pin trim pot I desoldered from an old board. I am assuming maybe it is a dual gang poteniometer or something with a common ground pin. Does anyone have any ideas what the actual pinouts could be and how I can test it to check? There is number on the side that says 2889, but I am not sure what that means (I doubt its a part number). Here are some images of it: enter image description here

enter image description here

  • \$\begingroup\$ My guess it that it is a coil/transformer (one side centre-tapped) from an old radio, withg an adjustable coild. \$\endgroup\$ – Wouter van Ooijen Mar 18 '15 at 22:24
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    \$\begingroup\$ Usually you can remove the metal case easily, and then it is revealed that this is a trim inductor. \$\endgroup\$ – PlasmaHH Mar 18 '15 at 22:41
  • \$\begingroup\$ FYI, I would guess the markings are a date code. 28th week of 1989. \$\endgroup\$ – Karl Bielefeldt Mar 18 '15 at 22:42
  • \$\begingroup\$ It's definitely not a pot and definitely is an RF inductor or transformer. Try searching for a company called coilcraft or even murata. \$\endgroup\$ – Andy aka Mar 18 '15 at 22:45
  • \$\begingroup\$ It was from a radio actually, but there were a ton of these everywhere. At least 15 or so. Could it be an RF inductor then? \$\endgroup\$ – electricviolin Mar 18 '15 at 22:47

Most likely, it's a variable-frequency tank circuit. Try this for a test.

Measure the resistance between the 3 in-line pins. Probably you'll find that the center pin has equal resistance to the 2 ends. Now look at the other two pins. If they read open, then most likely those pins are a variable capacitor, and the adjustment slot varies the capacitance. Basically, it looks like


simulate this circuit – Schematic created using CircuitLab

(Ignore the + on the cap symbol.)


It looks like a an IF transformer.

This will usually have two windings with one being tapped.

Depending upon the particular application it will probably have a capacitor across the tapped winding to make it resonate at either 10.7MHz or 455kHz.



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