potentiometertools
Is there any special tool used to adjust trimmer potentiometers?
I have some similar to the one on the picture:
I've tried using small slot, Phillips and Pozidriv screwdrivers, but they all don't seem to fit nicely giving me impression that there is some special tool used to adjust trimmer potentiometers.
If there isn't any special tool, what has proven to work well for you?
Given that you've said R7 is set to 0 ohms, the two fixed terminals of R6 are shorted together. When the wiper is at either extreme, its resistance to either fixed terminal will also be 0 ohms. When the resistance is 50%, both halves will be in parallel. Given that this appears to be a 50 k pot, we'd expect
$$R_{eq}=\frac{R_{max}}{2}||\frac{R_{max}}{2}=\frac{R_{max}}{4}=\frac{50000}{4}=12500$$
just as you measured.
Yep, as @Andy aka noted, you want to swap your red lines. The result should look like this:
simulate this circuit – Schematic created using CircuitLab
Here is a pretty good resource: http://www.beavisaudio.com/techpages/Pots/ There is a section on volume control that reiterates the circuit above.
Best Answer
Goot Zirconia Cross Screwdriver for Electronics DIY
This is a very interesting key for those who working with radio, or anything else that requires adjustment in bobbins, trimpots, trimmers and the like.
Its tip is a type of a white ceramic (the package says "zirconia" but it is actually Zirconium dioxide), which gives a high stiffness and does not change the tuning coils because it is not obviously of magnetic material.
Source (Portuguese): http://badulaquesdachina.blogspot.com/2010/03/chave-de-alinhamento-de-ceramica.html