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Troubleshooting Guide
The following guide should help in solving any problems encountered with
your signal tracer. First, check your unit for soldering or wiring errors.
Next, check the voltage at the emitter of transistor Q1. It should measure
between 4.5 to 5.5 volts. If you still have a problem, refer to the following
sections for help.
I. LED does not light:
A) Be sure the red clip is connected to a positive voltage between 5 to
40 volts, and the black clip is connected to ground.
B) Check the LED, it may be in backwards or open.
C) If 4.5 to 5.5 volts is present at the emitter of transistor Q1, proceed
to II.
D) Check the zener diode D1, transistor Q1, and capacitors C5 and C6
for backwards installation.
E) Make sure R9 and R10 are not interchanged.
II. Weak or no sound in earphones with green clip connected
to probe tip, and the LED is on:
A) Check to see if the IC is in backwards.
B) Must determine if the oscillator or amplifier is at fault.
If an
oscilloscope is available, look at the output of the op-amp (pin 1).
There should be 3 to 5V of a 1kHz squarewave.
If no scope is available, put the switch to tip receive position and
remove the green alligator clip from the tip. Touch the tip with your
finger. The earphone will buzz with 60Hz response when the gain
control is fully clockwise and the amplifier is operational.
C) If the oscillator is at fault:
Check the LM-358 op-amp (pins 1, 2, 3, 4, and 8), resistors R1 to
R6 and capacitors C1 and C2 for soldering or wiring errors.
Replace the LM-358 op-amp if there are no solder or wiring errors.
D) If the amplifier is at fault:
Check the LM-358 (pins 4 to 8), trim pot R11, resistors R7, R8, and
capacitors C3 and C4, for soldering or wiring errors.
Replace the LM-358 op-amp if there are no solder or wiring errors.
E) Check switch S1.
