Help with JFET switches

[drummer4gc]

Hey all,

I've got a Boss RV-3 that's not letting signal through one of it's JFET switches, Q2. It's a 2sk880. Didn't have one, so I replaced it with another Boss mainstay, a 2sk30a. No dice. I'm assuming there are different relevant characteristics between these two JFETs, but don't understand enough to know which spec matters. I'm assuming the 2sk880 turns on at a lower voltage than the 2sk30a - where should I be looking in the data sheet to confirm?

RV-3 Schematic: http://i.imgur.com/Fnmm3lQ.jpg (huge, so I didn't embed)

Thank you!

[anotherjim]

JFET is normally on and needs to be turned off with negative gate. Not letting signal thru implies the gate is always negative from the Source/Drain voltage.
I'd have expected the substitution to work, as the 30A is used in similar 9v circuits.
Is there half supply (Vref) on the Source?
Does the cathode of the gate diode get to 0V to turn 'em off? And then go up toward +9v to turn on? Latter case tricky as it's all high impedance and your meter will load the reading down to less than 9. But it only has to get close to Vref to allow it to turn on.

[Transmogrifox]

I agree with anotherjim it is more likely a problem with supporting circuitry than the FET itself. 

[drummer4gc]

Thanks for the advice, it was spot on! I'm still a bit confused by the voltages I was getting; they were inconsistent, which I think is related to the challenges of probing an SMD circuit. However, I was able to notice inconsistencies by comparing voltages between the two JFET switching arrangements and trace it to a capacitor, which needed some resoldering. Works great now, thank you!