Heathkit IG-4505 - Page 40

Page 40
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Recheck the wiring. Trace each lead in colored pencil
on the Pictorial as you check it. It is frequently
helpful to have a friend check your work. Someone
who is not familiar with the unit may notice
something you have consistently overlooked.
Check all component leads connected to the circuit
boards. Make sure the teads do not extend too far
through the circuit board and make contact with other
connections or parts, such as shields or the chassis.
Check all of the wires that are connected to the circuit
boards to be sure the wires do not touch the chassis or
other lugs. Make sure all wires are properly soldered.
If the difficulty still is mot cured, read the
“Precautions for Bench Testing’’ section, and the
section titled ‘“Troubleshooting.”’
Precautions for Bench Testing
WARNING: The full AC line voltage and high voltage DC is
present at several points in the calibrator. Be careful to avoid
electrical shock when working on the Calibrator.
@
Be cautious when testing transistors and integrated
circuits. Although they have almost unlimited life
when used properly, they are much more vulnerable to
damage from excessive voltage and current than other
circuit components.
Be careful so you do not short any terminals to
ground when you make voltage measurements. If the
probe should slip, for example, and short out a bias or
voltage supply point, it may damage one or more
components.
ad Do not remove any components or circuit boards
while the Oscilloscope Calibrator is turned on.
bad When you make repairs to the Calibrator, make sure
you eliminate the cause as well as the effect of the
trouble. If, for example, you should find a damaged
resistor, be sure you find out what (wiring error, etc.)
caused the resistor to become damaged. If the cause is
not eliminated, the replacement resistor may also
become damaged when the Calibrator is put back into
operation.
° Refer to the ‘X-Ray Views,” ‘Component Charts,”’
and the ‘Schematic Diagram” to focate the various
components.
e Use a high impedance voltmeter and an oscilloscope to
make the specified measurements in this section.
° If you suspect that a transistor is defective, first
measure the base-to-emitter voltage (Vbe). This
voltage is normally between .6 and .8 volts. If the
voltage is above this range, the transistor is open. If
the voltage is 0 volts, the transistor may be shorted or
a base-to-emitter short exists (possibly on the foil side
of the circuit board).
NOTE: In an extreme case where you are unable to resolve a
difficulty, refer to the ‘‘Customer Service’ information
inside the rear cover of the Manual. Your Warranty is
located inside the front cover.
Troubleshooting
\
The following symbols and protedures are used
in the troubleshooting charts:
Follow the “YES” arrow when you obtain the
proper measurement or condition.
Follow the ‘““NO” arrow when you do not obtain
the proper measurement or condition.
me This symbol, “APPROXIMATELY EQUAL
TO,” before a voltage measurement indicates
that this voltage may vary as much as +20%.
e All voltages given in the troubleshooting charts
were taken with a normal line voltage of 117
VAC.
e Components are listed in the order in which
failure or a problem is most fikely to occur.
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