Trimpot problem

[codog]

I seem to have a trimpot problem in the biasing section of Dr Boogey. The whole sweep of the trimpot only changes the voltage from 9.26v down to 9.16v. And this happens with all 4 trims. Any ideas what might be wrong?
Thanks,
      Clay

[alanlan]

Have you used the correct value of trim-pots?

Check all component values, orientation of transistors and wiring.

[axg20202]

+1. It's so easy to accidentally use trimmers marked '100' where '100K' are specified. That would be the first thing to check.

[codog]

The side says 100k and when it is at "full" and "empty" I get readings of ~110K and 0 ohms. When i measure the resistance from my +9v line to the drain, there is the resistance of whatever I set the pot to. That means I have it connected properly, doesn't it? And also, I don't have the transistors in, I'm just measuring the socket. Should I have them in?

[slacker]

You need to have the transistors in when you set and measure the voltages.

[codog]

Well there's my problem. Could you explain to me why they have to be in? I can't see why it would be necessary. Thanks again.

[railhead]

The current is passing through them -- they're a critical part of the circuit path.

[axg20202]

The side says 100k and when it is at "full" and "empty" I get readings of ~110K and 0 ohms. When i measure the resistance from my +9v line to the drain, there is the resistance of whatever I set the pot to. That means I have it connected properly, doesn't it? And also, I don't have the transistors in, I'm just measuring the socket. Should I have them in?

Doh! No worries - I challenge anyone around these parts to claim they've never embarked on at least some preliminary 'debugging' only to discover they've forgotten to put the IC or transistors in their sockets!  Stands to reason - if the circuit isn't complete it won't function like the complete circuit.