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Analysis of maintenance: because the net is difficult to look up information on the power amplifier circuit, the protection circuit with common amplifier protection circuits are different, so refer to the circuit board protect parts are hand-drawn circuit diagram, as shown in Figure 1. V2 use the TL074 part op-amp, as signal input V4 is the JRC4558, phase transformations and relay control signal output.YFmservice manual download site
YFmservice manual download site
When the amplifiers signal input through V4 and V2 amplifier transformed to charge the C37, V4 ¢ß feet DC control voltage output negative Q1 turn-on relay closing; when the amplifier when output over-current and over-voltage, protecting signals by changing to the Q7 's base, the Q7 C37 turn-on discharge, V4 ¢ß foot output voltage increases Q1 cutoff relay release.YFmservice manual download site
YFmservice manual download site
Maintenance comparison model of another piece of PB 12 Bass Amplifier Board. Two subwoofer models, power output and the voltage is different, but the whole structure is the same, only part of the component parameters are not the same, it is estimated that such circuits in active subwoofer JBL occupy a certain proportion of.YFmservice manual download site
YFmservice manual download site
PB 12 protection circuit is normal, powered on with no input signal, measured with multimeter two critical point voltage amplifier protection circuits, found no difference in the input signal, PB12 V4 ¢ß foot output DC control voltage from +10V to -12.7V, relay suction,YFmservice manual download site
E150P V4 feet voltage does not change, estimated to be components of the signaling pathway on issues, or amplifier output protection signals. In the case of power failure, use a multimeter on the measurement of the electrical blocking signal path of the related components and connections, found chip resistors R61 feet with circuit board solder resistance is too large, carefully observe the solder solder less, should belong to less Tin in SMT production process, by welding, and troubleshooting.YFmservice manual download site
YFmservice manual download site
Maintenance summary: patch in the production of circuit boards, circuit boards are generally used for SMT production line welding manual Visual inspection to check the solder quality, low Tin solder, when you didn't find in Visual inspection, although censorship could pass, but in the long run, due to oxidation and vibration may cause the solder connection is bad. Therefore, please install the subwoofer (or active speakers) produced by SMT surface mount technology PCB, in inspection and to be aware of the little Tin solder inspection.
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