The voltage on the diode won't reveal much, its the current thats the important figure. And that brings another problem because laser diodes are very static sensitive although in circuit there is less of a problem.
I understand what you say regarding accessability... I don't know what to suggest tbh. Maybe there are dedicated jigs and extension leads available but that's hardly a diy option.
It may or may not be a faulty pickup and without the detailed checks needed its not possible to say.
I understand what you say regarding accessability... I don't know what to suggest tbh. Maybe there are dedicated jigs and extension leads available but that's hardly a diy option.
It may or may not be a faulty pickup and without the detailed checks needed its not possible to say.
Normally you measure the volt drop across the resistor to get the current. The laser should only be "lit" for the brief moment that the focus search operation is being performed. After that it is turned off. A typical laser current is in the 50ma region but its very device dependent and unless you have the exact value the individual pickup was calibrated at then the measured value can only be a rough guide that the laser is at least drawing somewhere in the expected current range. In full size players many pickups have the value incorporated as part of the pickup serial number for reference.
For general info...
If you take a laser diode and gradually increase the current from zero then it functions first as a side emitting red LED. There is no laser action. As the current increases more and more then suddenly lasing begins and the optical output increases dramatically. From this point a tiny further increase in current causes a massive increase in the optical output. Go a bit to high and the laser is damaged or destroyed. Its a fine window of operating current that is needed and is why the laser diode has an integral photodiode to monitor the "optical" output and maintain the "optical" output at an exact level. The current varies according to temperature and also as the laser ages. The laser power control circuit always tries to maintain the optical power at a constant level by altering the current but this current is always within a fairly narrow window.
For general info...
If you take a laser diode and gradually increase the current from zero then it functions first as a side emitting red LED. There is no laser action. As the current increases more and more then suddenly lasing begins and the optical output increases dramatically. From this point a tiny further increase in current causes a massive increase in the optical output. Go a bit to high and the laser is damaged or destroyed. Its a fine window of operating current that is needed and is why the laser diode has an integral photodiode to monitor the "optical" output and maintain the "optical" output at an exact level. The current varies according to temperature and also as the laser ages. The laser power control circuit always tries to maintain the optical power at a constant level by altering the current but this current is always within a fairly narrow window.
If all checks point to the laser then it its time to look at replacement. I couldn't turn anything up on the KSS 602.
Have you checked to make sure that the spindle motor servo output and motor drive really is "non functional". We're assuming the pickup isn't focusing and that the system control isn't getting the Fok (focus OK) signal.
Its worth looking at the problem from another angle.
Have you checked to make sure that the spindle motor servo output and motor drive really is "non functional". We're assuming the pickup isn't focusing and that the system control isn't getting the Fok (focus OK) signal.
Its worth looking at the problem from another angle.
During focusing:
I cheked RF amplifier output with oscilloscope - no signal.
On the photodiode output (that one to control laser output power) : voltage level ca. 200mV, change to zero when trying to focus, not always, 1 of 5.
Another possibility is RF amplifier CXA2521 damage.
I didn't check RF amplifier input due to lack of space. I have to solder some wires to connect the oscilloscope.
What do you think I am supposed to check more.
I cheked RF amplifier output with oscilloscope - no signal.
On the photodiode output (that one to control laser output power) : voltage level ca. 200mV, change to zero when trying to focus, not always, 1 of 5.
Another possibility is RF amplifier CXA2521 damage.
I didn't check RF amplifier input due to lack of space. I have to solder some wires to connect the oscilloscope.
What do you think I am supposed to check more.
All I could think of was to check the spindle motor drive amp during focus search. That would be just to confirm that the motor isn't spining up purely because there really is no spindle drive output from the servo. Very unlikely the problem would be there but it just covers all bases before deciding the pickup is faulty. Any measurements would have to be done during the brief focus search time.
And never overlook supplies. Are they all correct and not low. Once you've done all that then the pickup is the most likely suspect.
And never overlook supplies. Are they all correct and not low. Once you've done all that then the pickup is the most likely suspect.
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