Yaesu FT-901DM Maintenance Service Manual page 78

AUDIO HUM
In some early models of the FT-901, a slight hum
could be heard on receive; this is most easily
observed by rotating the AF and RF gain controls
to zero. The problem was a ground loop, and this
bulletin will detail the simple modification to cure
the problem.
1. Refer to the drawing. Locate MJg on the
bottom of the chassis.
2.Cut the ground leads from pin 17. Cut the
ground lead from the left side of pin 14.
— ORIGINAL—
AF UNIT MJ6
SERVICING
MODIFICATION
3. Locate the cable whose center conductor is
connected to pin 12. Remove the shield of this
cable from pin 14, and reconnect it to pin 17.
4. Locate the two cables whose center conductors
are connected to pin 16. Their shields should be
removed from pin 17, and connected to the
ground point previously connected to pin 17
from the right side.
5. And the 0.1 uF 25 WV capacitor between pins
14 and 17, as shown. A ceramic capacitor is OK
in this application.
6. Connect a jumper between MJ2, pin 1, and MJs,
pin 1. This completes the modification.
Jumper MJ2—MJS pins |
Cut GND leads to PINI7
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