The right channel is silent, the left channel sound small, signal input selection failed. Regardless of the input from the VCD,DVD,TAPE there is sound, volume potentiometer adjustment does not work.qpGservice manual download site
qpGservice manual download site
Teardown observations found two D1266 have burnt fried right channel power amplifier tube, two negative feedback resistor has an open circuit. The signal selected by CD4052, high bass control with LM348 and SC9153 for electronic volume control, to facilitate overhauling real draw right circuit as shown in Figure 1.qpGservice manual download site
qpGservice manual download site
qpGservice manual download site
We can see from Figure 1, this is a classic DCL amplifier circuit. Two C1815 simple single differential input circuit A1015 and two 4007 bias circuit, C1815 and D1266-NPN composite pipe A1015 D1266 PNP-type composite pipe together with audio signals in polarity of the amplifier driving the speakers. After inspection, two D1266 breakdown, two resistors (0.33 ω) open V4-emitter breakdown, 270 ω resistor circuit.qpGservice manual download site
qpGservice manual download site
D1266 with substitution of plastic C5198, the other parts using the same model to replace, and then power up test, right back to work. Teardown 4052 directly replacing the original CD4052, sound source selection back to normal, but still sound small. Directly across from the CD4052 output L,R signals treble bass output, volume change, volume control is also normal,qpGservice manual download site
qpGservice manual download site
LM348 a problem with the circuit board. LM348 circuit board power supply 12V normal measurement, replace double-treble and bass control potentiometer is not valid. No LM348 due to checked information, in order to ensure the effect of treble and bass control, salvaged from a discarded card a piece based on the four amplifiers LM324 treble and bass control,qpGservice manual download site
qpGservice manual download site
CD4052 between the electronic volume control input and output strings, dual potentiometer using a thin wire attached to the LM324 panel circuit board, completed the transformation test, treble and bass control effective troubleshooting.qpGservice manual download site