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[ J6.
HUM TEST FOR ANALOG FUNCTIONS.
If previous
checks did not isolate the problem, turn the volume control
for maximum output. Momentarily touch a powered-up AC
soldering pencil on the center tap of the volume control.
CAUTION
DON'T use a soldering iron over 40 watts. Cordless irons
will NOT work for this test.
Listen for a low hum or click. This indicates that amplifier
U1 (TDA2002), the volume control, sound cabling and
speaker operate satisfactorily.
If you don't hear anything, repeat the test with the volume
control turned halfway down. This new test determines
whether the volume control is faulty. Also check cable con-
nectors for improper mating and broken wires .
SOUND INTERFACE BOARD
INTRODUCTION
The Sound Interface Board permits the Control Board to
reset the Sound Board. The negative 12 volt, sound
amplifier supply for also resides on the Sound Interface
Board.
There are two types of problems associated with Sound In-
terface Board failures... (1) No sound, or one sound stuck
on. (2) Heavily distorted sound. Before proceeding, isolate
the problem to the Sound Interface Board by replacing it
with a board you know to be good.
NO SOUND, OR ONE SOUND STUCK ON
Check the reset circuit on the Sound Interface Board. This
circuit includes chips U1 and U2. Also check the sound-
select lines. These run between the Control Board, Sound
Interface Board and Sound Board. The sound-select lines
connect to chip U1 at pins 1 through 6, 11 and 12. An addt-
tional strobe line from the Control Board connects to chip
U2 at pin
3.
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