Kenwood TH-77A Service Manual page 11

IH-//A/E
CIRCUIT DESCRIPTION
(4) Power Supply Circuit
External power is always supplied to 1C8 and IC13. The [C8 out-
put is sent to 1C10 and IC12. Therefore, the current for IC8 and
1C13 and the microcomputer backup current flow when the
power is turned off with the battery connected. The PW port of
IC10 is made low when the power is turned on. Q20 (1/2) is
then turned on. As a result, a reference voltage is applied to
each regulator. Power is supplied to the CTCSS unit when Q20
(2/2) is turned on. (See Figure 7.)
The 5C and 5R signals are produced by Q5 and Q6. A5T signal
is produced by Q8 and Q9. The 5C, 5R, and 5T signals are dis-
tributed by each switch. The reference OSC power for the
phase-locked loop (PLL) circuit is supplied from the 5C signal.
The 5RV, SRVC, and 5CV signals are turned on during VHF re-
ception. The 5RU, 5CU, and 5RU signals are turned on during
UHF reception. The 5TV and 5TU signals are turned on accord-
ing to the band in use during transmission.
(5) Save Circuit
Q7 is controlled by the SAVE pin of 1C10. The 5C and 5R regula-
tors of Q5 are then turned on or off to reduce the mean current
consumption. The automatic power-off (APO) function inter-
rupts all power supplies to circuits except the microcomputer
by turning off Q20. APO operation thus results in the much the
same current consumption as when the power is off.
d
SRUC
SRV
SCV
SRVC
sRU
ice scuU
S- 812506
STV
Ic10, 1c 12
Q20 2/2
Fig. 7 Power supply circuit
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