Fostex X-24 service manual Playback Frequency Response Calibration, Erase Current Adjustment

X-24

3)Playback the TCW-231 test tape and check the output level if it is -10 dBV (0.3 V) ± 1 dB reading.

4)If the reading is not within the above range, adjust R106 ~ R406 on the R/P AMP PCB assy.

3-9. Playback Frequency Response Calibration

1) Set the controls as follows.

Record track select switch: OFF

Dolby B noise reduction on/off switch: OFF

2)Connect an AC volt meter to the TAPE OUT 1 through 4 pin jacks respectively.

3)Playback the TCW-284F test tape and adjust R103 ~ R403 so that the output level at 6.3 kHz is 0.5 dB lower than the 400 Hz output level.

4)Confirm that the output level at 12.5 kHz is within ± 1 dB of the 400 Hz output level.

3-10. Erase Current Adjustment

At adjusting the erase current, put a blank cassette tape to the transport and the track to be adjusted is put in REC mode. Assuming the track 1 to be adjusted, the oscilloscope probe is connected to the test point TP106 on the R/P PCB assy and rotate and fix the core T101 for minimum voltage point. Then, confirm that the voltage at TP105 is more than 55 mV.

NOTE: If the voltage at TP106 is adjusted at minimum, the erase current flowing the erase head is set to the maximum.

Adjust the remaining tracks in the same way.

Track 2: Adjust T201 for minimum voltage at TP206. Then, confirm that the voltage at TP205 is more than 55 mV.

Track 3: Adjust T301 for minimum voltage at TP306. Then, confirm that the voltage at TP305 is more than 55 mV.

Track 4: Adjust T401 for minimum voltage at TP406. Then, confirm that the voltage at TP405 is more than 55 mV.

3-11. Coarse Bias Adjustment

At coarsely adjusting the bias current, put a blank cassette tape to the transport and the track to be adjusted is put in REC mode. Assuming the track 1 to be adjusted, the oscilloscope probe is connected to the test point TP104 on the R/P PCB assy and rotate and fix the pot R133 (220 kΩ) at 60 mV.

Adjust the remaining tracks in the same way.

Track 2: Adjust R233 so that the voltage at TP204 is 60 mV.

Track 3: Adjust R333 so that the voltage at TP304 is 60 mV.

Track 4: Adjust R433 so that the voltage at TP404 is 60 mV.

3-12. Record Level Calibration

*The procedures up to 3-10 must be completed before proceeding to this adjustment.

1)Put a blank cassette tape to the transport and apply a 400 Hz, -10 dBV (0.3 V) sine wave signal to the INPUT 1 and 2 phone jacks. (In the case the signal is input from XLR jack, the terminal No.3 (COLD) and No. 1 (GND) must be shortened.)

2)Set the controls as follows.

Record track select switch: All tracks ON (Confirm that the REC TRK LEDs (1 ~ 4) are blinking.)

Trim knob: At minimum

Dolby B noise reduction on/off switch: OFF

3)Connect an AC volt meter to the TAPE OUT 1 ~ 4 pin jacks.

4)Put the transport into REC PAUSE mode and adjust the Input Fader so that the level at TAPE OUT 1 ~ 4 is -10 dBV (0.3 V).

5)Release the PAUSE button and start recording the signal.

6)After recording a certain length, rewind the tape to the start point of recording section. Then, playback the tape and

check the level at TAPE OUT 1 ~ 4. If the AC volt meter reading is not within -10 dBV (0.3 V) ± 0.5 dB, adjust the pot R121 ~ 421 (22 kΩ) on the R/P PCB assy.

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