Filter Characteristic.

   Input signal is applied to the Circuit I/P and is monitored at TP1
     1a - checks the mid band gain
     1b and 1c - the bandwidth ie O/P should not have dropped to half
     1d and 1e - checks the cut off and should be less than half
                 the mid band gain.

   If low or no signal the fault is in the amplifier.
   Is 5V present? check for 5V rail on TP5V.
   if so Suspect Amplifier Q1,2,3,4 Voltage on TP1 should be ÷ 1.8V.
   Check for Transistor type, orientation.
   Check values, Soldered joints, and look for solder bridges.

   If filter Characteristic is wrong then Suspect filter components.
   Check values, R4, C6, L1, C7, L2, C8, R7 AND soldering.

