PHILIPS FWC399
Service Manual

9-3

Brief introduction

General 1. Playback Mode 13. Motor Speed (For FR versions only)

Signal playback head A or Deck B is selected and fed by Mode Selector IC7710 (HEF4952BT). During High speed dubbing, a feedback signal from uP through pin 03 of IC7610 (HEF4094BT) will trigger the The signal is amplified by amplifier IC7720 (AN7323S) before feeding IC7740 (HEF4952BT) out AF Board transistors 7622 (BC847B) 7616 (BC857B) to cause a change in the voltage level between High and Low, thus changing

via connector 1701. speed of the motor. 14. IC7610 (HEF4094BT) 2. Recording Mode

Recording Signal selected fed through Mode Selector IC7710 which then amplified by IC7610 (HEF4094BT) is a Shift Register use issues the logic for cmos switch ICs (HEF4952BT) via 1A0, 2A1 and 2A2.

amplifier IC7720 (AN7323S). The amplified output signal will pass through IC7730 (HEF4952BT) for record equalization It also issues logic to On/Off SOL_A, SOL_B and MOT. Recording speed is controlled via NS/HS. back to IC7710 (HEF4952BT) before registered into the Rec/PB Head of Deck B.

3. Dubbing Mode

In Dubbing mode, signal from playback head Deck A is selected and fed through by the Mode Selector IC7710 Circuit (For sets with Dolby B NR version only) (HEF4952BT) which then equalised for playback mode by the amplifier IC7720 (AN7323S) so that a flat response is 15. IC7630 (CXA1551M) IC7630 (CXA1551M) circuit is a Dolby Reduction Type B IC for Playback and signal. Noise obtained after pre-amp. The equalised signal will then follow same path as in the Recording mode. Reduction ON/OFF are controlled by DOLBY, which CLK, direct from uP. After clocking in DATA, CLK is set to HIGH/

4. Mode Selector LOW for NR OFF/ON.

The Mode Selector IC7710 (HEF4952BT) caters for 4 inputs signal, namely from Deck A, Playback Signal The filters 5631 & 5632 (LXD-210) in Dolby circuit is for purpose of filtering the 19kHz Pilot Tone (for Tuner

from Deck B, Recording Signal and Dubbing Signal. 16. 19kHz Filter

5. Amplifier PB/REC signal only) of the Recording signal. 17. Level Adjust The Variable resistor 3635, 3636,3641 and 3642 in circuit is for adjusting playback level of the Dolby reference 6. Automatic Level Control (ALC)

Amplifier IC7720 (AN7323S) is for purpose of amplifying Playback and Recording signal from the Mode Selector.

ALC circuit consists resistors (3760, 3765, 3766, 3767), capacitors (2762 2763) and control by transistor 7787 (BC847B). (400Hz , 200nWb/m). 7631, 7632 are ON to enable adjustment of 3641, 3642 during Playback Deck A. Transistor ALC limits the amplifier output a constant value when input signal becomes too large, thus limiting recording current to 7633, 7634 and 3635, 3636 are active for Playback Deck B. 18. Amplifier IC7640 (NJM4560M)

below saturation level, to prevent recording distortion.

7. Muting Circuit (For Non-Dolby version only) The Amplifiers 7640A & 7640B (NJM4560M) in Dolby circuit is for purpose of amplified the Recording signal.

Switch S4 IC7740 (HEF4952BT) is for purpose of muting the output during mode. During Recording The circuit which consists transistors 7788, 7789 and 7790 (BC847B) is for purpose of muting the output during

mode, S4 is closed and shorted to the ground. 19. Muting Circuit

8. IC7740 (HEF4952BT) Recording mode.

The function of the IC7740 (HEF4952BT) is to change time constant between 120us Ferro I) and 70us Chrome (IEC

II) during playback mode. It will automatically determined whether the tape type is 120us Ferro I) or 70us Chrome (IEC II). This IC will switch to Flat Gain during the Recording mode.

9. IC7730 (HEF4952BT) CR Chrome (IEC type II)

NOTATIONS & ABBREVIATIONS USED IN THIS DOCUMENT

The function of the IC7730 (HEF4952BT) is change gain time constant according to tape type and recording speed DB Dolby NR type B boost current at higher frequency during recording to compensate for head loss. It will automatically determined DD Double Deck

whether the tape type is 120us Ferro I ) or 70us Chrome (IEC II). DM Double Motor

11. Bias Symm (For Dolby B NR version only) ND Non Dolby

FE Ferro (IEC type I) FF Non-Autoreverse 10. Bias Level FR Autoreverse Deck B Bias Level making use Variable resistor (3773) adjusting optimal level of the bias current for Ferro or Chrome. Gnd Ground x HSD High speed dubbing

Bias Symm making use of Variable resistor (3785) adjust bias current for left and the right channel to be equal. NR Noise Reduction

NSD Normal speed dubbing REC Record Playback Switch which consists FETs 7785 (For Dolby B NR version only) & 7786 (J111) is for the purpose of providing S/A Sub-assy a virtual ground for Rec/PB Head (Deck B) during mode. During Playback mode, the FETs are turn on and SD Single Deck shorted pin 2 and 4 of connector 1720 ground. During Recording mode, FETs are turn off to allow the oscillator SM Single Motor

12. Switch PB Playback

to be superposition onto the Recording signal for recording.