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TEST/DIAGNOSTIC PROCEDURES
(Continued)
NO SOUND DURING THIS TfST{but
sound can be heard during the Diagnostic Tests).
Check the sound-select inputs (pins 2 through 9 of U9) to see if they pulse during Sound Test
01. Also, check the -12 V supply voltage on the CPU Board. If this voltage is low (or AC ripple
seems too high), perform the following checks:
1. The gray and gray-green transformer secondary wires for 19.4 VAC.
2. The CPU Board filter capacitor C26 for -12 VDC.
3. The filter capacitor C26 for excessive AC ripple (over 0.75VAC}.
If the 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.
rc&mO©1Nl
DO NOT use a soldering iron over 40 watts. Note also that cordless soldering
irons will NOT work for this test.
Hearing a low hum or a 'click' indicates that the power amplifier (U1, TDA2002), the Volume Con-
trol, and the speaker are operating satisfactorily, as is the sound circuit cabling. Not hearing a
sound requires repeating the test with the Volume Control turned part way down, to determine
whether the Volume Control is faulty. Also, check the cable connectors for proper mating, and
that no broken wires affect this circuit.
TAXI 34
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