Akai GX 747 Service Manual

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Akai GX 747 Service Manual

Extracted text from Akai GX 747 Service Manual (Ocr-read)

Page 18


x l—>to lCl,2®
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Fig. 25
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TRSI 23C345Lififll T397 I23C345L(P,Dl

® Microcomputer Resetting Circuit
(Refer to Fig. 25)

A reset circuit is provided in order to eliminate
the memory of the electronic counter and 0
Slop when power is supplied.

When power is turned on, the voltage (HOV)
is supplied to the base of TR54 through C44
and R164 to turn TR$4 0N, i. e, the collector
of TR54 will be “I." to turn TRSS OFF
through Rl68 which means the collector of
TRSS will be “l-l’l Then “H" is supplied to
Terminal of [Cl and ‘2, and when Terminal

7. becomes “H”, the microcomputer is reset
When the charging to C44 is completed, TRS4
is turned OFF, TRSS ON and Terminal

; Timer Starting Circuit (Refer to Fig, 26)


When power is switched ON, the base ofTRSl
is turned “H" through C49 and R88 of the Pre


Fig. 26

Amplifier RC Board and through D54 and
Rl58 of 117 of the Syscon PtC Board.
The collector becomes "L" to turn TR63 0N
throu \ RZOSr The “H" from 317 makes
1C7 “H" through 053, R155 and R156,
and at the same time, “H" is supplied to 1C7
through D53, RlS’Z and R153. Depending
on the condition of the collector of TR96, the
output to 1C7 ® or [C7 is determined
and the direction of FWD or REV is determinv
ed. If the collector ofTR96 is “L”, [C7 © be-
comes “H".

Therefore, “H" goes into [C7 © and @ ,the
167 (‘9 becomes “L“.

TR60 is energized through D56, i. e., FWD


Same as for REC TIMER START, bm due to
the lack of input in TRSI. FWD or REV PE is
achieved instead of REC.