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VMmservice manual download site
The machine power input circuits is relatively simple, power Jack DcJACK, isolating diodes D1, 4. 5V battery and Zener diodes zD1. Before starting the measured battery voltage is 4. 5V, the rectifier output voltage is 4.3V, are normal. After you press the power switch on, ZD1 voltage is only 1.8V, and upper and lower volatility, suspect ZD1 leakage damage. Remove ZD1, its forward resistance 5.8k ω, the reverse resistance 36k ω (infinity), has been damaged. The tube has not see models, circuit board labeling 8.2V/1W parameter selected Motorola's production of 1 N4738A replacement, measuring the online resistance slowly rises above 10K, indicates that the power supply input leak current fault is excluded. Power on power on test radio function has returned to normal.VMmservice manual download site
Discussion: ZD1 is the input power supply over voltage protection diode, in order to prevent damage caused radio circuit rectifying power supply wrong setting. ZD1 is damaged, the regulated parameters do not have to ask, pick just 1W, Zener diode substitution between 6V~8.2V it.VMmservice manual download site
VMmservice manual download site
Example 2: press "start" button does nothing, it will not power on, display no display and machine does not work.VMmservice manual download site
Analysis of maintenance: in order to improve the technical performances, this machine uses the grouping supply means, composed of Q19~Q24 electronic switch control. Under normal conditions, loading batteries or plug in the external power supply for Q21 R45 turn-on a positive bias, Q20 base via the R46, Q21 ground conduction and A11 terminals supply voltage through Q20, plug-in added to CPU power end of 53 feet, boot for work. At this point press the power switch (POWER),VMmservice manual download site
VMmservice manual download site
CPU34 foot output goes high, A3 by plug-in terminals, R49 Q23, Q19, Q24, conducting. Which, power voltage by Q24 plus to double channel amplifier CXA1622 Krispy Kreme feet, main for power larger of audio amplifier level powered; while, the voltage by Q20, and Q19 for tuning voltage VT boost circuit, and band conversion control circuit 74LS138 of 16 feet, and radio circuit TA8132AN ¢Ý feet, and FM/AM tuning and the in the put circuit, circuit powered, also by plug-in A10 Terminal to CPU reset circuit (R82, and reset switch), and LCD LCD display, powered.
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