Yaesu FT-840, Service Manual

Page: 11 / 152

The FT-840 is carefully designed to allow
the knowledgeable operator to make nearly all
adjustments required for various station con­
ditions, modes and operator preferences sim­
ply from the controls on the front and rear
panels, without opening the case of the trans­
ceiver. These adjustments, plus certain inter­
nal settings, are described in the FT-840
Operating Manual.
The following procedures cover the some­
times critical and tedious adjustments that are
not normally required once the transceiver has
left the factory. However, if damage occurs
and some parts are subsequently replaced, re­
alignment may be required. If a sudden prob­
lem occurs during normal operation, it is
likely due to component failure; realignment
should not be done until after the faulty com­
ponent has been replaced.
We recommend that servicing be performed
only by authorized Yaesu service technicians,
experienced with the circuitry and fully equip­
ped for repair and alignment. So if a fault is
suspected, you should contact the selling
dealer for instructions regarding repair. Auth­
orized Yaesu service technicians have the lat­
est modification information, and realign all
circuits and make complete performance
checks to ensure compliance with factory spe­
cifications after replacing faulty components.
Those who do undertake any of the follow­
ing alignments are cautioned to proceed at
their own risk. Problems caused by unauthor­
ized attempts at realignment are not covered
by the warranty policy. Also, Yaesu must re­
serve the right to change circuits and align­
ment procedures in the interest of improved
performance, without notifying owners.
Under no circumstances should any align­
ment be attempted unless the normal function
and operation of the transceiver are clearly
understood, the ca use of the malfunction has
been clearly pinpointed and any faulty com­
ponents replaced, and the need for realign­
ment determined to be absolutely necessary.
Alignment
The following test equipment (and thor­
ough familiarity with its correct use) is neces­
sary for complete realignment. Correction of
problems caused by misalignment resulting
from use of improper test equipment is not
covered under the warranty policy. While
most steps do not require all of the equipment
listed, the interactions of some adjustments
may require that more complex adjustments
be performed afterwards. Do not attempt to
perform only a single step unless it is clearly
isolated electrically from all other steps .
Rather, have all test equipment ready before
beginning, and follow all of the steps in a
section in the order they are presented.
0
Digital DC Voltmeter (high-Z, > 1 MQ/ V )
D
RF Millivoltmeter
D
AF Millivoltmeter
D
RF Standard Signal Generator w
I
cali­
brated output and dB scale, 0 dBµ= 0.5 µV
D
AF Signal Generator with calibrated out-
put
D
Frequency Counter
D
50-Q Dummy Load (150 - 250 watts)
D
16.6-Q Dummy Load (>150 W)
D
In-Line Wattmeter (150 - 250 W, 50-Q)
D
RF Attenuator (> 150-W, 40-dB) or coupler
Alignment Preparation
&
Precautions
A 50-Q dummy load and inline wattmeter
must be connected to the antenna jack in all
procedures that call for transmission, except
where specified otherwise. Correct alignment
is not possible with an antenna.
Except where specified otherwise, the tran­
sceiver should be tuned to 14.200 MHz, USB
mode, and these controls set as indicated:
0
MOX
&
VOX
buttons OFF
(•)
0
AGC-F
button ON (-.)
0
ATI, PROC, AGC-F & NB
buttons OFF
(•)
0
SOL &
RF PWR
fully ccw (minimum)
3-1
FT-840 Technical Supplement