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11-07-2000
P10501A07.DOC
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Maintenance instruction Premium 10501
1.2 Laser current measurement instruction
The laser current of the VAU1254 can be measured and gives an indication is the laser is damaged or
end-of-life. The following instructions describe how the laser current can be measured.
Measuring conditions:
- Ambient temperature 25 degree Celsius
- Measure after 5 minutes of play
Remark:
Laser current will increase at higher ambient temperatures!
1. Put the CD unit in play mode with a clean not scratched disc, preferably a test disc like SBC444 or
SBC444A, and play track 1.
2. Measure the DC voltage across the 4E7 safety resistor R3208 [1]
3. Put the CD unit in stop mode, (the laser is switched off now).
4. Measure the DC voltage across the 4E7 safety resistor R3208 in mode stop [2]
5. Calculate the laser current as follows
Laser current = (voltage [1] - voltage [2] ) / 4.7 ohm
The calculated value should be within 50 and 100 mA. (Nominal 75 mA)
This calculation assumes that the difference in current consumption of the pre-amplifier between play
and stop mode can be neglected, and that resistor R3208 has a nominal value of 4.7 ohm.
Remark:
This measurement method should be used only to check if the laser is still operating well within the
specified laser current. The location of resistor R3208 can be found in the component placement sheets
and is located close to the micro controller between the micro controller and the power connector.
© 2000 Philips Electronics N.V. All rights reserved
Philips components
Page 7
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