Omeg pot replacement help

[m23585]

I need help to find a replacement for this potentiometer with switch. But I'm not sure if this is linear or logarithmic. Could anyone help me with that? It's from Viking VK20 metal detector (on/off + sensitivity adjustment). The design doesn't have to be the same as long parameters will be, I believe.




Thanks

[migusch]

Hello, m23585!
I can decipher "100KA" from the picture. 100Kohms does not need any further comment.
The Letter A for the taper is not that easy to interpret because there is no reliable rule that manufacturers follow.
Wikipedia writes:
"A letter code may be used to identify which taper is used, but the letter code definitions are not standardized. Newer potentiometers will usually be marked with an 'A' for logarithmic taper or a 'B' for linear taper. Older potentiometers may be marked with an 'A' for linear taper, a 'C' for logarithmic taper or an 'F' for anti-logarithmic taper. The code used also varies between different manufacturers."

In the case that the potetiometer is still working from an electrical point of view (albeit the shaft might be difficult to turn...) you can still measure the taper. Try to turn the shaft in a 50%-position and measure the resistance between the middle pin and consecutively both outer pins. When you have around 50kohms in both cases you have a linear taper, when both values differ much it seems to be logarithmic taper. As a control whether the poti still works (in electrical means) both resistance-values should sum to 100k in each taper.

If its linear taper you can buy it at maplin:
http://www.maplin.co.uk/p/omeg-100k-...h-switch-fw45y
There are a lot of electronic stores to buy from and google is your best friend...

good luck,
migusch

[migusch]

Oops - forget my link...
I did not see that your potentiometer is PCB-mounted.
migusch

[m23585]

Does it make a difference that it's pcb mounted? Because I was thinking to use wires to solder points on pcb. I just need to make sure I will have proper replacement. Will try your method, looks quite easy to check, even for me


Thanks a lot

[migusch]

Does it make a difference that it's pcb mounted?

It depends on how your detector is physically constructed. Usually the potentiometer is mounted at the front panel and in your case the pcb seems to be directly behind the front panel. If there is enough space between both it won't be any problem to connect the potentiometer via wires.

[m23585]

Is this linear then, on one leg shows 50, another about 46? And I checked the space, should be enough to put there 'normal' type of pot.

[migusch]

Yes, it seems to be linear. When I wrote both resistance-values add up to 100k I forgot the word 'almost' as the tolerance of potentiometers is usually up to +-30%
When you write " 'normal' type of pot" I guess you mean an ordinary pot without switch. But then you have to add a further switch to the front panel if you need the switching-function.

[sinclairuser]

as far as i know silverdog stocks 100 meg pots with built in switches, ebay has loads, even board mount type, there are not hard to find.

[m23585]

Well, now it should be easy to find. Thanks guys.

[6666]

Do you have a multi meter ?

just open up the pot, its only 4 tabs, and measure the track by moving probe along the track.

[m23585]

Problem sorted. Thanks guys