Check the waveform at pin 14 of the U4 socket with an oscilloscope. You should see a
square wave with 5Vp-p. Adjust VR1 to make sure that the oscillator frequency can
change between 3 to 150Hz. Check VR1, R15, C4 and C5 if the oscillator is not
working. Also check the voltage at U2 pin 4. It should be near 5.0V for the oscillator to
work. If it is less than 3.0V, check the bypass lead on U3 socket.
Check pin 14 of U5 socket. You should get identical signal since the two pins are
connected together.
Figure 4. Oscilloscope waveform of counter clock in Test 2B.
Test 2B without oscilloscope
Without an oscilloscope, you can measure the DC level of the clock signal. This can
give you some indication of the oscillator output although it is not as reliable as an
oscilloscope.
Disconnect the power and install a bypass lead between pin 2 and pin 14 of U3 socket.
Do not install U3 through U8. Use the test setup shown in Figure 4.
