25K is not enough resistance to stop the signal from getting through the high frequency signal path. But you wouldn’t get an accurate reading anyway unless you unsoldered the jumpers…the dc voltage from opamp pins will skew the reading of your ohm meter. The most likely cause is a bad solder joint somewhere. Make sure everything is soldered correctly…including the jumpers. You can double check that the high frequency optocoupler led is being lit up by making a tiny incision with you xacto knife (about 1mm long) on the heat shrink on the back side of the led (close to the led’s leads). That way you can see if the led is actually bright when it’s supposed to be bright (when the depth knob is at 0, for example…or when in calibration mode on the high harmonic mix setting).
If the LED is turning on then the problem has to be in the high frequency signal path somewhere…most likely a bad solder joint. Use the schematic to trace out the components in the high frequency path and then look for bad solder joints in those areas.
Let me know what you find.
-Brach