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Sunday, January 29, 2017

When the Current Regulation Pot Fails!


When your "Current Regulation" pot fails there is a better part to replace it with.
This new pot is $6.99 and features 10 turn linear resolution with a smooth rotary action.


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For other information on the K40-S build use the  K40-S BUILD INDEX with schematics


The wipers fold back.
I guess I turn the pot to fast!
There are supposed to be multiple wipers. 


Getting the knob off was a B*%^+. I had to grab the shaft with a vice grips. Then wedging a flat blade between the vice grips and the knob I pried it off. I think the knob was glued on ..... seriously!

After the gripping experience with the knob the rest was easy. Simply wire in a new pot.
This one is a linear multi-turn wire wound pot which gives much better current resolution and feels nice!

Purchase here

Note: these pots are often not avialable. Any 5K pot will work. The 10 turn ones give you finer control.

Wiring & Diagram

The replacement is pretty simple if you pay attention to the pots connections when you take the old one out. The only confusion might be that the new pots connections are not in order. The wiper is the first pin (2) from the end opposite the shaft.
If the pot operated backward reverse the leads 1&3.

Here is some help ....

Careful the wiper is on the left.

Pot with DVM current readout
I wired in a plug to make disconnect easy and modular

Installed in the panel 


I added a DVM across the pot so that I could get a digital representation of the pots postion and the relative current. 
When setting up a job type I record the digital value and then next time I do that same job I just reset the pot to that value to accurately repeat the setting.

Note: you need a 3 wire DVM so that you can read from 0.

See the wiring diagram above for installation.

The green film in this pack works for a filter when making a plastic bezel .


This knob might look nice and installs with a set screw.

Purchase here

Enjoy and comment
Maker Don


  1. Thank you for the post, it helped me fix my potentiometer design!

  2. Hi Don,
    thanks for all the work you've shared with the K40 community!
    As I have only rudimentary electrical knowledge (I know ow to spell "Ohm") you see me puzzled. My K40 came with an analog ampmeter, however adjusting the power is not very precise and you could easily exaggerate turning the knob.
    You have replaced the pot with a better one (I guess this is a drop in replacement ???) and in additon you have wired a voltmeter.
    What is not clear to me is what tells the voltmeter in addition to the ampmeter?
    Should I adjust the laser power according to the voltmeter? What are the corresponding values (i.e. 20mA corresponds to xyz volts?)
    Greetings from Germany

  3. I added a a analog ma gauge, a 10 turn pot, laser test fire button, and used the original laser on off switch. But now when I turn on the original switch the laser fires. Any help would be greatly appreciated. Thanks for your hard work and information, it has help me greatly.