Bad pots or bad parts

[hari]

I built Marshal Shredmaster from http://www.handmades.com.br, it sound heavy and i like it. But I found that there 3 pots that not response (contour, graves, agudos). is that problem because of bad pots or bad parts? anyone have the same experince like this?

ty

[RaceDriver205]

The chance of the parts or pots being faulty is near zero. Most likely a bad connection.

[Mark Hammer]

Not necessary.  I've had plenty of pots that were the source of nonfunctionality in my projects.  Occasionally they are dirty inside.  Occasionally the rivets that secure the resistive strip to the solder lugs are not tight enough to provide continuity.  And sometimes, when installing the pots into a chassis and twisting them around, the wire leads can be too short and tug the lugs close enough to short against each other.  Sometimes that tugging and twisting results in leads snapping at the solderjoint in the process.  It can also be the case that closely spaced pots may seem to have their lugs away from each other, but when you go to tighten the nuts on the outside of the chassis, they move over a few degrees here and there inside the chassis and before you know it they are shorting out against the case or another pot.

These days I always do the following:
1) Take the back off the pot and clean and pretreat it with chemicals
2) Give the rivets a little pinch with my needlenose pliers to secure them (easier to do without damage when the back is off)
3) Cover the solder lug and first little bit of the lead with heat shrink tubing so that it doesn't short out against anything and to provide some strain relief for the solder joint.

This has helped to improve my rate of fires-up-first-times considerably.

[Paul Perry (Frostwave)]

That's very true Mark, but the odds against THREE dud pots in one project...... unless they are salvaged from somewhere....

[Mark Hammer]

That's very true Mark, but the odds against THREE dud pots in one project...... unless they are salvaged from somewhere....

True.  Of course, all it takes is just one bad pot, shorted lug, or snapped lead to create nonfunctionality.  I don't know about you, but I don't know from which direction someone will collide with my vehicle, so I insure all four sides...and the top and bottom.   Similarly, I take precautions with all my pots because I don't know where the problem is going to happen, only that it WILL happen if I don't take precautions.

[petemoore]

   If the pots wired, you *may [small percentage of the time] have to remove an alternate path through the circuit by disconnecting it...
  Anyway you can just measure the pots from wiper to outside lug, wiper to other outside lug...to see if there are any dead spots, and across the outside lugs to find the value of the pot.
  Another thing I like to do while I'm in there is to check for *bad ground connections where ground connections *arent' marked on the schematic.