Yaesu FT-757GX II, Technical Supplement

Page: 9 / 70

PER FORMA N C E I MP R OVEMEN T MODI FI CAT I ON S
Serial numbers are composed o f a letter and a
number, indicating the date o f manu facture,
followed by six digits. The first two digits (closest
to the date code) are the Production Lot number.
So, for example, serial number O C l
23456
is from
Production Lot
12,
set number
3456.
Be fore
making any modification, make sure that it applies
to the Lot number o f the particular transceiver
being modified.
Also, be fore making any modification, check to see
i f it has already been carried out by a Yaesu agent,
dealer or previous owner.
QSK Keying Stability
The following modification may be made to
improve the stability o f QSK operation, i f it is
found to be unstable. This modification has
already been carried out in some Lot
4
trans­
ceivers, and in all transceivers having serial numbers
above
XX050000
(Lot
5).
The diagrams below and on the following pages
indicate the changes to be carried out on the PA
Unit and RF Unit during the following steps:
LOCAL UNIT
INH
©
®
®
CD
' '
SPLICE: :
1
. Re ferring to page
1 1
,
disconnect the trans­
ceiver from the power source and remove the
covers.
2.
Referring to the lOO W PA Unit diagram on the
following page, locate P 42 and cut the blue
wire at pin
5
(INH signal) o f this plug. Do not
disturb any other connections on this Unit.
3.
Now re ferring to the RF Unit diagram on the
following page, solder a
5
cm extension wire to
the end o f the blue wire removed from the
lOOW PA Unit, and then carefully insulate the
splice with vinyl tape. Solder the other end o f
the extension to the end o f R 1257 exposed on
the component side o f the RF Unit.
4.
Route the blue wire care fully so that it will not
be pinched when replacing the boards and
covers, and then reassemble the parts removed.
This completes the modification.
MC140118
J6003/P42
IOOW
PA UNIT
I
RF
UNIT
I
I
I
01060
I
MCl40118
01058
I
2SA733AO
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