Daewoo DV-K784N-JJ, Service Manual

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59
4. HI-FI AUDIO CIRCUIT
1) How to make TA1246F fo adjustment-free
In TA1246F, Zener Zap (the way to destruct Zener Diode) is used for making FM modulation fo adjustment-free. As it is basically simi-
lar to OTP (One Time Memory), fo of the IC is already set by IC makers so its adjustment is not required. For your reference, how to
adjust fo is explained as below;
(How to adjust Zener Zap fo)
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Figure 1 shows VCO (Voltage Control Oscillation) adjustment circuit. In case of the IC without setting, i.e, Zener Zap is not con-
ducted, its fo can be adjusted by Bus Data. In TA1246F, 255 per channel can be adjusted by Sub Add No. 5 and 6 step by step.
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After fo adjustment, input ZAP pulse adjusts Data. (Zener Zap)
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One Zener Zap is completed, the adjusted fo will be kept without extra input of Bus Data.
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ZAP pulse In is usually grounded as shown the above Figure 2.
Clock
Data
Regulation
ZAPI
ZAP pulse IN
Variable by Bus
Rec FM Out
Lch : 8bit
Rch : 8bit
Bus
Control
VCO
Adj.
Clock
Data
Data cannot be inputed
Constant
Rec FM Out
Bus
Control
VCO
Adj.
Fixed
Fig. 1
Fig. 2