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Power Supply Circuit
The power supply circuit regulates a constant output voltage +5.6V by T1 and D4.
D2
Power Switch
ON
DC +7.5 V
Input
OFF
GND
Nature of Trouble
No power
No sound at all
Keyboard LEDs don't
light up
A certain key or switch
does not function
Certain keys or switches
do not function
T1
2SD1858Q,R
R1
GND
TROUBLESHOOTING
Faulty Block
Power Supply Circuit
Power switch
Power Jack (J1)
Power Amp.
(IC1: AN8053N)
CPU (LSI1: MSM6521-13)
Oscillator (XL1)
Keyboard LED
Keyboard LED Matrix
Key and Switch Matrix
Key and Switch Matrix
— 5 —
R3
R4
R2
R5
R6
DG
AG
Checkpoint
Base of T1 should receive +6 V.
Emitter of T1 should provide +5.6 V.
Switch contact.
Jack contact.
Pin 16 should receive +7.5 V when the
power switch is turned on.
Voltage at pin 14 should drop at 0 V
when the power switch is turned on.
Check output signal of pin 1.
Voltage at pin 27 should rise 0 V to 5.6
V when the power switch is turned on.
Pins 39 ~ 46 should provide pulses.
Pin 29 should have a sound signal when
a key is pressed.
Pins 20 and 21 of the CPU should
receive an ocsillation signal.
Open circuit on LX or LY line.
Dust on the contact.
Open circuit on KC or KI line.
VDD +5.6V
AVDD +5.6V
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