Hitachi HCUR700UC Service Manual page 11

I O P M E A S U R E M E N T M E T H O D
When measuring Laser drive current (Iop), playback the discs (CD, DVD) described below, measure Iop for CD Laser and
DVD Laser by the test point (LD1 - LD4) on the SERVO P.W.B.
TEST DISC : DVD / DVDT-S01 (Manufactured by ALMEDIO INC)
CD / TCD-784 (Manufactured by ALMEDIO INC) or commercially available Discs.
LD3
LD2
LD1
` LD4
R148
R147
Mechanism Unit bottom side
O P T I C A L P I C K U P D I A G N O S T I C S A N D R E P L A C E M E N T
NO DISC indicated,
Playback not smooth, etc
• Laser drive current check
• HF signal check
Present value :
50% up to initial value
Traverse Unit replacement
(refer to the next page)
Laser drive current check
after replacement. If the
present value is less than
80mA, write on the new
label by hand, put on the
new label over the old label.
1. DVD Laser current measurement
LD2
LD1
(1) Connect the oscilloscope GND side to test point LD1 near R147 and oscilloscope signal side to
test point LD2 near R147.
(2) Playback the title 1 / chapter 1 of the DVD Test Disc.
(3) Measure the voltage between LD1 and LD2, calculate Iop as follows.
Measurement Voltage Value
Iop =
39 (Resistance Value)
2. CD Laser current measurement
(1) Connect the oscilloscope GND side to test point LD3 near R148 and oscilloscope signal side to
test point LD4 near R148.
(2) Playback the track 1 of the CD Test Disc.
(3) Measure the voltage between LD3 and LD4, calculate Iop as follows.
Measurement Voltage Value
Iop =
39 (Resistance Value)
When repairing, carry out failure diagnostics by following the procedure
described below.
If the present value of the laser drive current is 50% up to initial value, it is the point
of the pickup replacement.
In case of the pickup replacement, replace the Traverse Unit with no adjustment.
The initial value is indicated on the label on back side of Mecha.
If the present value exceeds 80mA,
replace the Traverse Unit with a new one.
Cause : Damaged electrostatically when replaced.
– 11 –
+
– Oscilloscope
HCU-R700