Test 1C: IC output short-circuit
This is an important test ensure that no output pin of any IC is shorted to the power or
the ground network. This condition often causes large current to flow through the ICs
leading to permanent damages. Do not insert U2 through U8. Do not apply any power to
the circuit during this test. Set your DMM to beeping continuity test or resistance
measurement. Measure the resistance of an output pin at an IC socket to the ground.
The resistance should not be near zero. Otherwise you have a short circuit at the pin.
Repeat the same test from the IC outputs to the +5V power network.
Test 1C: Test-points for IC output pins. No
power should be applied. No pin should be
shorted to power (+5V) or ground.
U2 pins 5, 9
U3 pins 1, 2, 12, 13
U4, U5 pins 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 12
U6, U7, U8 pins 10, 11, 12, 13, 14, 15, 16
Test 1D: IC sockets power supply
In this test, we want to make sure that power is properly reaching all IC sockets and
there is no short-circuit of the power supply network. Do not start this test if Tests 1A,
1B or 1C have not passed.
Disconnect power from the power jack. Do not install any ICs U2 through U8. Use a
DMM to measure the resistance between pin 14 and pin 7 of U2. It should be about 4K
Ohms. This is from the internal resistance of U1 (78L05). If this resistance is only
several Ohms, you have a power-ground short. Check your soldering work to locate the
problem. Do not power up the circuit when there is a power-ground short.
If all power network tests have passed, apply battery power 8 – 12VDC to the power
jack. Measure the voltage across the following pairs of power supply pins of the IC
sockets. The voltage should be 5.0V +/- 5%. Figure 2 shows the test setup. U6, U7 and
U8 do not have +5V power supply.
Measure the current consumption. It should be less than 5mA.
Do not install any IC into socket until Tests 1A, 1B, 1C and 1D all
passed. Doing so may cause IC damages. Check your soldering work.
