Marantz PM7200 can work in categories a and b and is a pure class a music amplifier, manufactured by Amoi Electronics, this is can be seen from PCB process, obviously more than the coarser in @# the production machines and solder levels were relatively poor. After the malfunction of the machine is turned on there is no sound output, relays do not snap, this amp is no screen, LEDs do not display properly, without blinking. No fault seems to only proceed from the circuit test.TqKservice manual download site
Part level after the first judgment, plus or minus 55 v power supply, the output relays without voltage, access signal circuit can measure to the amplified signal, plug the speaker cable connected directly, sound output to normal, explain later-stage amplifier circuit is no problem. The relay drive circuit and protection circuit.TqKservice manual download site
TqKservice manual download site
Protection circuit and drive circuit of core components are using of is compared common of TA7317P, this components alone installation in a PCB Shang plug received amplifier Hou level circuit board, 7317 of 1 feet for had flow detection, 2 feet for output voltage detection, measurement Shi are no found exception, 9 feet powered is with a star 22K resistance from +VB,5 feet negative powered with a star 10K resistance from-VB,8 feet tube of is delay drive following electrical, with a star 220K resistance and 47UF capacitor from 9 feet take to charging, When 8 pin voltages up to 1.3 volts, the relay sucks and.TqKservice manual download site
TqKservice manual download site
Here to note a problem, 7317 is by short received following electrical coil of cathode to achieved control of, that 4 feet and 6 feet connected, so no connected Shi 6 feet can didn't to following electrical coil anti-back of 24 v voltage, even will a, b channel of switch disconnect also can didn't to, because this paragraph amplifier of headphones interface also design has a following electrical, marking for 5270, it of coil 24 v voltage is a power on some, so don't thought measurement to has three a coil Shang are has 24 v on think not normal.

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