The most likely reason is damage to the output amplifier. To verify that this
is the problem, turn on the unit, increase the amplitude, and check for an
output signal at U4 pin1. If the signal is missing, then please contact
customer service [(800)-772-8700 x 78] to return the unit, referencing this
If the signal is present, then the output circuit needs to be replaced,
which consists of the following chips: U4 (430-095), Q1 (420-002),
and Q2 (420-003).
After replacing the output op amp, you will need to calibrate the bias current
of the output amplifier:
- Set the output amplitude to minimum.
- Set the output frequency to 5 kHz.
- Adjust R32, the blue pot that is closest to TP3 and above
U4, until you obtain a a reading of 0.017 - 0.035 V across
TP3 and TP4 (located to the right of U4).