Heathkit TA-16 - Page 36

Page 32
Tests and the Signal Tracing sections tell how
to search through the amplifier to find a dif-
ficulty. The Hum Tests use a method that does
not require electronic test equipment. The Sig-
nal Tracing section requires the use of a signal
tracer or an oscilloscope.
Before you try to locate the cause of a diffi-
culty, be sure you are operating the controls
correctly. See the Operation section on Page 30.
CAUTION: The power transformer, AC socket,
primary circuit breaker, and the On-Off-On
switch all have AC line voltage applied to them.
Use caution when testing to avoid electrical shock.
GENERAL CHECKS
The following general checks should be made if
the amplifier does not operate properly after
the kit is assembled.
1. Recheck the wiring. Trace each lead in
colored pencil on the Pictorials 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 some-
thing consistently overlooked by the builder.
2. 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 reheat-
ing all connections 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 the pilot
lamp lights up.
4. Check the values of the parts. Be sure that
the proper part has been wired into the
circuit, as shown in the Pictorial diagrams
and called out in the wiring instructions.
It is sometimes easy to misread the third
color band on a resistor. For example,
if a 3300 n (orange-orange-red) resistor
were installed instead of a 33 KS/ (orange-
orange-orange) resistor, the circuit would
not operate properly.
5. Check for bits of solder, wire ends or
other foreign matter which may be lodged
in the wiring and for solder that may be
bridged across the circuit board foils.
6. If, after visual checks, the trouble is still
not located and a voltmeter is available,
check voltage readings against those shown
on the Voltage Chart (fold-out from Page 28)
and the Schematic Diagram (fold-out from
Page 41). NOTE: All voltage readings were
taken with an 11 megohm input vacuum tube
voltmeter. Voltages may vary as much as
±20%.
7. A review of the Circuit Description will
prove helpful in indicating where to look
for trouble.
TESTING PRECAUTIONS
When testing the amplifier, make certain the
speaker leads are not short circuited, as this
could damage the output transistors or other
circuit components in the amplifier. When
making voltage measurements, be careful that
you do not short across adjacent foils on the
circuit board, or between two terminals, or
from a terminal to ground. For instance, if the
voltmeter test probe should slip and short out a
bias or supply point in the power output stage,
it is almost certain to damage one or more
transistors or diodes.
Never remove or install transistors while the
amplifier is turned on or you may damage some
of the other transistors. Although transistors
have almost unlimited life when they are used
properly, they are much more vulnerable to
damage than vacuum tubes. A vacuum tube,
for instance, may be operated under shorted,
zero-bias, excessive voltage, or high-current
conditions for at least short periods of time
without materially damaging the tube; but any
one of these same conditions can completely
destroy a transistor instantaneously.
THE CIRCUIT BREAKERS
The circuit of your Guitar Amplifier is pro-
tected by two circuit breakers, one in the pri-
mary winding and the other in the secondary
winding of the power transformer. If your
amplifier should ever go completely dead and
the pilot lamp goes out, there may be a short
circuit somewhere that has caused a circuit
breaker to open up. Use the following pro-
cedure if you suspect that one of the circuit
breakers has opened.