These checks and adjustments must be performed in the sequence described.
The laser diode must not yet have been fitted to the PCB.
Neither U2 nor U3 should yet be fitted into their sockets.
All other components should have been fitted to the PCB.
Apply power to the UPNLT. LED1 should light.
Check that there is +5V +/- .2V on pin 10 of U2. If not, this problem must be remedied before continuing with setup and adjustment.
Disconnect the power supply to the UPNLT.
Fit U2, the 555 timer IC, into its socket.
Apply power to the UPNLT. LED1 should light.
LED2 should light for a period of 5 to 10 seconds, then extinguish. If not, this problem must be remedied before continuing with setup and adjustment.
Disconnect the power supply to the UPNLT.
Solder a temporary wire link across R1.
Connect a 47R resistor between the LDK and PDK/LDA points on the PCB. (This resistor simulates the laser diode during these adjustments.) It is easiest to solder this resistor to the short leads already connected to these points.
Set VR1 to mid position.
Set VR2 fully clockwise.
Connect a multimeter set to a range suitable to read a current of around 50 mA between pin 1 of U3's socket (the corner pin closest to VR2) and 0V.
Apply power to the UPNLT.
Adjust VR2 slowly anticlockwise to give a reading on the multimeter of 50 mA. Try not to overshoot significantly, as this may damage VR2 and/or Q2.
Disconnect the power supply from the UPNLT.
The temporary link fitted in step 3 should still be in place.
The 47R resistor fitted in step 3 should still be in place.
Connect a 47K resistor between the PDA and PDK/LDA points on the PCB. (This resistor simulates the monitor photodiode during these adjustments.) It is easiest to solder this resistor to the short leads already connected to these points.
Set VR1 fully clockwise.
Connect a multimeter set to read a current around 20 mA between pin 1 of U3's socket and 0V.
Apply power to the UPNLT.
Adjust VR1 slowly anticlockwise to give a reading on the multimeter of 20 mA +/- 5mA. This adjustment is quite sensitive and some instability is normal. A reasonable effort to set the current to 20 mA suffices.
Disconnect the power to the UPNLT.
Remove the temporary link across R1.
Remove the temporary 47R resistor fitted in step 3, and the temporary 47K resistor fitted earlier in step 4.
Fit U3, the CS8130CP transceiver IC, into its socket.
The laser diode may now be fitted.