Heathkit AR-14 - IN CASE OF DIFFICULTY; Visual Test Procedures; Bench Testing Precautions

~if·&iffHE;iJ
Page 55
IN CASE OF DIFFICULTY
This section of the manual is divided into three
parts: Visual Test, Precautions For Bench-
Testing, and the Troubleshooting Chart. Begin
your search for any trouble that occurs after
assembly by carefully following the checks
listed in the Visual Tests section. After visual
tests are completed, refer to the Troubleshooting
Chart.
Refer to the Service and Warranty sections of
the Kit Builders Guide in an extreme case, when
you
are unable to resolve the difficulty.
NOTE: Refer to the Circuit Board X-Ray Views
and photos on Pages 76 through 79 for the
physical location of parts on the circuit boards
and on the chassis.
VISUAL TEST
1. Recheck the w1rmg. Trace each lead in
colored pencil on the Pictorial as it is
checked. It is frequently helpful to have a
friend check your work. Someone who is not
familiar with the unit may notice something
consistently overlooked by the constructor.
2. It is interesting to note that about 90% of the
kits that are returned for repair, do not
function properly due to poor connections
and soldering. Therefore, many troubles
can be eliminated by reheating all connec-
tions to make sure that they are soldered
as described in the Soldering section of the
Kit Builders Guide.
3. Check to be sure that all transistors are in
their proper locations. Make sure each tran-
sistor lead is connected to the proper point.
4. Check the values of the parts. Be sure in
each step that the proper part has been
wired into the circuit, as shown in the pic-
torial diagrams. It would be easy, for ex-
ample, to install a 22 Kn (red-red-orange)
resistor where a 220 Kn (red-red-yellow)
should have been installed.
5. Check for bits of solder, wire ends or other
foreign matter which may be lodged in the
wiring.
If the trouble is still not located after the
visual tests are completed, and a voltmeter
is available, check voltage readings against
those shown on the Schematic Diagram and
voltage drawings (Figure 17 and 18 on Pages
74 and 75). NOTE: All voltage readings were
taken with an 11 megohm input vacuum tube
voltmeter. Voltages may vary as much as ±20%.
NOTE: A
review of the Circuit Description
may help you determine where the trouble
is •
PRECAUTIONS FOR BENCH TESTING
1. Be cautious when testing transistor circuits
that you do not operate the transistors be-
yond their limits. Although the transistors
have almost unlimited life when used prop-
erly, they are much more vulnerable to
damage from excessive voltage or current
than tubes. A vacuum tube, for instance, can
often be operated under shorted, zero-bias,
excessive-voltage, or high-current condi-
tions for short periods of time without
materially damaging the tube, but any one
of
these same conditions can completely
destroy a transistor instantaneously.
2. Be sure you do not short any terminals to
ground when making voltage measurements.
If the probe should slip, for example, and
short out a bias or supply point in the power
output stage, it is almost certain to cause
damage to one or more transistors or diodes.
3. Be sure the connections to the test equip-
ment are not crossed, thereby introducing a
short circuit across the amplifier output
(SPKR)
terminals. This could also damage
one or more transistors or diodes.
4. Transistors should be inserted or removed
only while the Receiver is turned off. If this
rule is not followed, transistors may be
damaged.