Yaesu FT-901DM Maintenance Service Manual page 68

SERVICING
MODIFICATIONS
VFO DRIFT IN PRESENCE OF VHF TRANS-
MITTER
Some transceivers from the first and second pro-
duction lots display a VFO drift problem in the
presence of a nearby 2 meter transmitter. The
problem is caused by a ground loop, and the
modificaticn below will eliminate the difficulty.
Modification Procedure:
(1) Refer to Fig. | , and cut the foil on the VFO
UNIT, PB-1440A, at the two points shown.
Install the jumper wire Shown in the drawing.
Q)
(3)
(4)
(5)
Refer to Fig. 2, and remove the ground lead
from pin 4 of Jso2. Re-route the lead so that
the connection is from pin 4 of Jgo2 to the
center hole under Cg22.
Change the screw adjacent to Cga2
NYLON screw.
Ad a new 0.01 disc ceramic capacitor between
pins 3 and 4 of Jsc2.
to a
Install a new ground lead, made from a heavy
braided wire of 100-120 mm length. This lead
should run from the VFO compartment to
the ground lug for the XTAL UNIT, as shown
in Fig.
[e)
Install jumper
="
Cut foil of Te
circuit Door: in
Oo
Figure |
Change to nylon screw
Lead from PIN3 of J802
to center hole under C822
Add CAP O.0luF = PINS
between PINS and PIN4
re Cut lead here
Instol new GND lead
from VFO box to XTAL UNIT
Length= 100—120mm.
Figure 3
3-13
Leod from pin3,J802
|
Figure 2
BOTTOM VIEW