PIONEER DEH-2750MP/XU/CN
Manual de Servicio

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1.3 AUTOMATIC ADJUSTMENT FUNCTION
This system automatically handles the circuit adjustment inside the CD LSI. All adjustments are performed whenever a disc is inserted or the CD mode is selected by pressing the source key. Each adjustment will be explained below.

A

1.3.1 TE, FE, and RF offset auto-adjustment
This adjustment is made to adjust the offsets of the TE, FE, and RF amplifiers in the preamplifier block to their target values on the basis of the REFO when the power is turned on. (The target values for TE, FE, and RE offsets are 0V, 0V, and -0.8V respectively.) <Adjusting procedures> 1) With the LD OFF status, the microcomputer reads each offset through the servo LSI. 2) The microcomputer calculates the voltages for correction from the measured values, and inputs the calculated results as the offset adjustment values.

B

1.3.2 Tracking balance (T.BAL) auto-adjustment
This adjustment is to equalize the pickup output offsets for E-ch and F-ch by changing the amplifier gain inside the LSI. Actually, the gain is adjusted so that the TE waveform becomes symmetrical on each side of the REFO. <Adjusting procedures> 1) The focus loop is closed. 2) The lens is kicked in the radial direction to make certain that the TE waveform is generated. 3) The microcomputer reads the TE offset calculated in the LSI through the servo LSI. 4) The microcomputer takes either of the following steps depending on the calculated offset: � When the offset is 0, the adjustment completes. � When the offset is positive or negative, the amp gains for E-ch and F-ch should be changed. The steps 2) to 4) are repeatedly taken until the offset becomes 0 or the repeating time reaches the limit frequency.

C

1.3.3 EF bias auto-adjustment
This adjustment obtains the best focus point during the play mode and maximizes the RFI level by utilizing the phase difference between the 3T level of the RF signal and that of the signal obtained when focus error disturbance is applied to the focus loop. At this moment, the auto-gain control (AGC), where focus error disturbance is applied to the focus and tracking loops, is also performed as explained below. <Adjusting procedures> 1) The microcomputer transmits the command to apply disturbance component to the focus loop (inside the servo LSI). 2) In the LSI, the 3T-offset component of the RF signal is detected. 3) From the relation between the 3T detected component and the disturbance, the LSI obtains the volume and direction of the focus offset. 4) The microcomputer transmits the command and reads out the detecting result from the servo LSI. 5) The microcomputer calculates the necessary correction and inputs the result as the bias adjustment value to the servo LSI. The adjusting steps are repeated a few times for higher adjustment accuracy as same as those for the AGC.

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E

1.3.4 Focus and tracking AGC
This function automatically adjusts the focus and tracking servo loop gains. <Adjusting procedures> 1) Disturbance component is applied to the servo loop. 2) The error signals (FE and TE) are extracted through the band pass filter as the G1 and G2 signals. 3) The microcomputer reads the G1 and G2 signals through the servo LSI. 4) The microcomputer calculates the necessary correction and performs the loop gain adjustment inside the servo LSI. For higher adjustment accuracy, the above steps are repeated a few times.

F

CX-3158

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