help with trimpot adjustment at drains of tc

[Marc.yo]

i am having trouble getting 4.5v or even close at the drains of the jfets on the thunderchief. i am getting like 8 volts minimum. what i am doing wrong?

[petemoore]

  Not necessarily 'wrong'...
  Start by reading the debugging page.
  For all we know it is a source follower that's working fine, the battery is approaching midlife crisis'.
  Find out what it is on your board that doesn't follow the schematic, using the DMM.
  Let's say it's a gain stage, and the battery is 9vdc.
  ..Jfet orientation is a good place to start [with data sheet of device used], also it's possible the gate  or source aren't seeing resistances which make the drain bias correctly, such as the source not being pulled toward Gnd. via S resistor.
  It may be possible to choose a Jfet which doesn't bias using the shown resistor values, trying another Jfet is a good suggestion, but before trying anything else I would follow the recommendations [requirements] RG wrote up to allow us to debug effectively.