Figure 6. Counter sync pulse at U4 pin 15.
Test 3 without oscilloscope
Disconnect power supply and insert U4 and U5, CD4017. Do not install U3, U6, U7 and
U8. Install a bypass lead between pin 2 and pin 14 U3 socket. The test setup is shown
in Figure 5.
Dial VR1 to the highest resistance for the lowest counting speed. Apply power and
measure the voltage at pin 1 of U4. Since the positive pulse only appears once every
ten clock cycle, the DMM will read near zero voltage when there is no pulse and near
5V when there is a pulse. However, many DMM voltage reading cannot response fast
enough to a short pulse and the voltage reading may not go up to 5V. If you see a
rhythmic rise and fall of the voltage reading with the low voltage near zero, the counter
is probably working. If you dial VR1 to the fastest counting speed, the voltage value
