Troy PL757A-tune the radio channel search operation and LCD display are normal, but the bands are silent,fMaservice manual download site
Analysis and repair: from the analysis of the phenomenon of failure, CPU operation and LCD display circuit of the control system is working properly, failure in audio power amplifier. The radio uses the high performance CXA 1622M stereo power amplifier IC, containing double preamplifier, dual power amplifier and electronic volume, operating voltage for the 1.8V~4.5V, ② foot external switchfMaservice manual download site
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(The stereo headphone jack EAR JACK control) BTLL (Mono, by speaker playback)/stereo (two-channel, stereo headphone playback) conversion, BTL power =110mW x 2. TA8132AN13, and 14 feet output of stereo audio signal by C39, and C42 coupled entered, C43, and C45 is negative feedback capacitor, C49 for left, and right channel frequency compensation capacitor, C46, and C47 is HF elimination noise capacitor, C48, and C50 for output coupled capacitor, 15 feet output 1.26V benchmark voltage, by volume regulation potential device VR1, and R30 points pressure Hou plus to 14 feet, by internal circuit for volume control. In addition, 14 foot CPU40 (MUT muting the foot control, the CXA1622M measured data as shown in table 3.fMaservice manual download site
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Perhaps silent failure mainly due to CXA1622M, an audio amplifier power supply disorders, uncontrolled electronic volume potentiometer or amplifier damage caused. Checked with Krispy Kreme pin voltage 4.25V normal (see table 3), the Earth Terminal II, f, 11, and 12 feet without unsoldering open. Measuring 14 feet volume control voltage is 1.26V, is muted. Voltage led to 14 feet high for two reasons: one is the output high CPU40 foot, second, 15-foot divider resistor R30 unsoldering or open circuit. Checking R30 end resistance have cracks, remove the measuring its resistance is infinite, already open circuit is damaged. 39k/0.125W carbon film resistor with a replacement after troubleshooting.fMaservice manual download site
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Discussion: except perhaps silent failure, a common failures and audio power amplifier circuit: 1. BTL speaker SP sound small and distorted when you insert a stereo headset, a channel properly, other-channel sound and distortion. This fault is the feedback capacitance C43, C45, leakage and poor headphones or speakers broken tray, moving coil magnetic gap and other debris. CXA1622M the normal PIN voltage measurement, only black-pin voltage 1.2V (normally 2.15V), positive and negative resistors are 72k Omega (infinite normal). External capacitor C43 leakage check black feet,

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