Daewoo DV-K784N-JJ, Service Manual

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TA1246F PNR system
It is possible to make the below system because TA1246F can have same VHS Hi-Fi characteristics even with less parts and less con-
stants.
• Playback and recording uses same circuit, which is located in feedback loop of MOS (Main OP Amp). The characteristics of
Emphasis and De-Emphasis can be acquired by controlling the feedback loop. So playback of self-record tape has good performance.
• The characteristcs mixed with FM Emphasis, NR Emphasis and Weighting can be shown by De-Emphasis and Weighting which are
different from the spec generally used so far. Hence, we can meet VHS spec even with less parts and less constants.
• Weighting characteristics is applied to rear part of PNR in Record mode and to front part in Playback mode, and NR (Noise
Reduction) can affect 20KHz LPF, and Dynamic Range can be protected.
IN
MOA
+
–
NR
DeEmph.
CCA
20k
Pin 30
PNR Monitor
20kHz
LPF
22k 2k
T1
T4
Pin 3/9
Vref
0.01µ
Pin 8/32
10µ
5.6k 18k
Pin 7/33 Pin 6/34
10µ
Peak
Det.
Weighting
sub
DeEmph.
T1
T2
T3
T4
Rec Out
DeEmphasis Time Const.
T1=240us, T4=20us
Weighting Time Const.
T1=240us, T2=56us
Sub DeEmphsis Time Const.
(Bulit in)
T3=24us, T4=20us
IN
20kHz
LPF
+
–
CCA
NR
DeDmph.
PB Out
T1
T4
Peak
Det
Weighting
Sub
DeDmph.
T3
T4
T1
T2
Fig. 4 Block Diagram of PNR Circuit (in Record mode)
Fig. 5 Block Diagram of PNR Circuit (in Playback mode)