PIONEER CDX-FM687/XN/ES
Service Manual

CX-892

5) Focus and Tracking Automatic Gain Control
This function is used for implementing automatic control of the focus and tracking loop gain. The following is the adjustment procedure : (1) Inject disturbance to the servo loop. (2) Extract the error signal (FE and TE) generated at when the disturbance is applied to obtain the signals G1 and G2 via the B.P.F. (3) The microcomputer reads the G1 and G2 signals via the LSI. (4) Based on the necessary correction calculated by the microcomputer, the LSI performs the loop gain adjustment. Above adjustments are repeated several times to ensure higher adjustment accuracy.

This adjustment takes place at the following timing : � When the focus close alone is completed during the setup process. � Just before the setup is completed (just before the play takes place). � After the off-focus has been corrected during the play.

7) Adjustment of Pre-Amp Stage Gain
It is used for adjusting the entire RFAMP (FE, TE and RF amplifiers) to +6dB or +12dB depending on given gain level when reflected light from the disc is significantly below the required level due to stained lens. This phenomena can be noticed when playing back the CDRW. The following is the adjustment procedure : When reflected light from disc is judged to be significantly below the required level during the setup, set the entire RFAMP to +6dB or +12dB. In this case, if the gain is modified, the setup have to be repeated from the first step. Through the adjustment, if you judged the play becomes available by setting the entire RFAMP to +6dB, +6dB should be selected for the setup next time on. See the figure below :

6) Automatic RF Level Adjustment (RFAGC)
This adjustment is used for implementing intended signal transmission successfully by adjusting unevenness of the RF signal (RFO) levels, that results from disc and machine relevant factors, to a target value. The adjustment is actually done by varying gain of the amplifier provided between the RFI and RFO. The following is the adjustment procedure : (1) Using the command, the microcomputer reads the output from the RF level detection circuit on the servo LSI. (2) Based on the read value, the microcomputer calculates an amplifier gain that will produce the target RFO level. (3) The microcomputer sends the corresponding command to the servo LSI so that the above gain value may be set.
Gain of entire RFAMP

Play the CD-RW with the gain being set to +12dB + 12dB

+ 6dB

yy y ,,
Play is started with +6dB judging the lens is stained Play at +6dB increases due to stained lens or other reasons (the typical gain is employed for the initial setup) Time

TYP

14

Fig.19 : CONCEPTUAL DIAGRAM OF PRE-AMP GAIN ADJUSTMENT