Laser Does Not Light; Focusing Failure; Hf Trouble - Sharp MD-R3 Service Manual

• Laser does not light

Is 5V applied to the pin 13 CD LD ON terminal of IC901?
Yes
Is +4.0V applied to the emitter of Q751?
Yes
Is +1.8V applied to the collector of Q701.
Yes
Is +1.8V applied to the pin 8 of CNP751?
Yes
Check CNP751. If it is normal, the optical pickup is defective.

• Focusing failure

Remove disc, and check whether the optical pickup lens
moves up and down.
Yes
Set disc, and check whether the following waveform appears
on the pin 8 of IC750.
Yes
IC750 is defective.

• HF trouble

Does output (tracking error signal) appear on the pin 4 of
TP751 in the CD TEST mode 3?
Normal
s the tracking gain adjusting VR752 set to minimum?
I
No
Does tracking output appear on the pin 17 of IC750 in the CD
TEST mode 4?
Yes
Does output appear between the pins 26 and 27 of IC700?
Yes
Check connection of optical pickup wire between IC700 and CNP751. If it is normal, the optical pickup is defective.
8 PIN
(FE OUT)
22 PIN
(FS OUT)
Abnormal
IC901 is defective.
No
Is +5V applied to the C751 side of
No
R753?
Yes
Check the pin 2 of BI851/CNS552A/B, and check +5V line of
SERVO.
Is +3.2V applied to the base of
No
Q751?
Yes
Q751 is defective.
PWB pattern breakage between Q751 and pin 8 of CNP751
No
Check as stated in item "Triangular wave for focus servo is
No
not output".
Set disc, and check whether the following waveform appears
No
on the pin 8 of IC750.
Check CNP751. If it is normal, the optical pickup is defective.
Adjust again tracking gain.
Yes
Check the peripheral parts of IC750. If it is normal, IC750 is
No
defective.
Check the peripheral parts of IC700. If it is normal, IC700 is
No
defective.
– 63 –
MD-R3
R753 is defective.
No
Check between the
No
base of Q751 and
the pin 6 of IC750.