9A-39A-3
Brief introduction
General
1.Playback Mode13. Motor Speed (For FR versions only)
Signal from the playback head Deck A or Deck B is selected and fed through by the Mode Selector IC7710 (HEF4952BT).During High speed dubbing, a feedback signal from the uP through pin 03 of the IC7610 (HEF4094BT) will trigger the
The signal is amplified by amplifier IC7720 (AN7323S) before feeding to the IC7740 (HEF4952BT) and out to the AF Boardtransistors 7622 (BC847B) and 7616 (BC857B) to cause a change in the voltage level between High and Low, thus changing
via connector 1701.the speed of the motor.
2.Recording Mode14. IC7610 (HEF4094BT)
Recording Signal is selected and fed through by the Mode Selector IC7710 (HEF4952BT) which is then amplified by theIC7610 (HEF4094BT) is a Shift Register use for 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 andIt 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 the playback head Deck A is selected and fed through by the Mode Selector IC7710Dolby Circuit (For sets with Dolby B NR version only)
(HEF4952BT) which is then equalised for playback mode by the amplifier IC7720 (AN7323S) so that a flat response is15. IC7630 (CXA1551M)
obtained after the pre-amp. The equalised signal will then follow the same path as in the Recording mode.IC7630 (CXA1551M) in the Dolby circuit is a Dolby Noise Reduction Type B IC for the Playback and Recording signal. Noise
Reduction ON/OFF are controlled by DOLBY, which is from CLK, direct from uP. After clocking in DATA, CLK is set to HIGH/
4.Mode SelectorLOW for NR OFF/ON.
The Mode Selector IC7710 (HEF4952BT) caters for 4 inputs signal, namely Playback Signal from Deck A, Playback Signal
from Deck B, Recording Signal and Dubbing Signal.16. 19kHz Filter
The 19kHz filters 5631 & 5632 (LXD-210) in the Dolby circuit is for the purpose of filtering the 19kHz Pilot Tone (for Tuner
5.Amplifier PB/RECsignal only) of the Recording signal.
Amplifier IC7720 (AN7323S) is for the purpose of amplifying the Playback and Recording signal from the Mode Selector.
17. Level Adjust
6.Automatic Level Control (ALC)The Variable resistor 3635, 3636,3641 and 3642 in the Dolby circuit is for adjusting the playback level of the Dolby reference
ALC circuit consists of resistors (3760, 3765, 3766, 3767), capacitors (2762 , 2763) and control by transistor 7787 (BC847B).(400Hz , 200nWb/m). Transistor 7631, 7632 are ON to enable adjustment of 3641, 3642 during Playback Deck A. Transistor
ALC limits the amplifier output to a constant value when input signal becomes too large, thus limiting recording current to7633, 7634 and 3635, 3636 are active for Playback Deck B.
below saturation level, to prevent recording distortion.
18. Amplifier IC7640 (NJM4560M)
7.Muting Circuit (For Non-Dolby version only)The Amplifiers 7640A & 7640B (NJM4560M) in the Dolby circuit is for the purpose of amplified the Recording signal.
Switch S4 of the IC7740 (HEF4952BT) is for the purpose of muting the output during Recording mode. During Recording
mode, S4 is closed and shorted to the ground.19. Muting Circuit
The muting circuit which consists of transistors 7788, 7789 and 7790 (BC847B) is for the purpose of muting the output during
8.IC7740 (HEF4952BT)Recording mode.
The function of the IC7740 (HEF4952BT) is to change time constant between 120us Ferro (IEC I) and 70us Chrome (IEC
II) during playback mode. It will automatically determined whether the tape type is 120us Ferro (IEC I) or 70us Chrome (IEC
II). This IC will switch to Flat Gain during the Recording mode.
NOTATIONS & ABBREVIATIONS USED IN THIS
DOCUMENT
9.IC7730 (HEF4952BT)CRChrome (IEC type II)
The function of the IC7730 (HEF4952BT) is to change gain and time constant according to tape type and recording speed
DBDolby NR type B
to boost recording current at higher frequency during recording to compensate for head loss. It will automatically determinedDDDouble Deck
whether the tape type is 120us Ferro (IEC I ) or 70us Chrome (IEC II).DMDouble Motor
FEFerro (IEC type I)
10. Bias LevelFFNon-Autoreverse
Bias Level making use of the Variable resistor (3773) for adjusting the optimal level of the bias current for Ferro or Chrome.FRAutoreverse Deck B
Gnd x Ground x
HSDHigh speed dubbing
11. Bias Symm (For Dolby B NR version only)
NDNon Dolby
Bias Symm making use of the Variable resistor (3785) to adjust the bias current for the left and the right channel to be equal.NRNoise Reduction
NSDNormal speed dubbing
12. PB SwitchPBPlayback
Playback Switch which consists of the FETs 7785 (For Dolby B NR version only) & 7786 (J111) is for the purpose of providingRECRecord
a virtual ground for the Rec/PB Head (Deck B) during Playback mode. During the Playback mode, the FETs are turn on andS/ASub-assy
SDSingle Deck
shorted pin 2 and 4 of connector 1720 to the ground. During Recording mode, the FETs are turn off to allow the oscillator
signal to be superposition onto the Recording signal for recording.SMSingle Motor |
ACEC
