Yaesu FR-50B, Instruction Manual

Page: 12 / 22

Page 12 of 22
MAINTENANCE
This receiver has been thoroughly adjusted with the aid of much
measuring equipment
by the manufacturer, so re-adjustment should not
normally be necessary fo r a long time. If, due to component change or
development of some fault, re-adjustment or repair should be found
necessary, then this should be attempted only after full
understanding of this booklet.
1. Removal of Chassis
After removing the four screws from the underside, push on the
front panel and withdraw from the rear.
2. Location of Faults
Measure voltages and make resistance checks using Table 1 and
Table 2 for reference. Any large departure from the values
shown in the tables could be an indication of the faulty
section.
Use the VTVM for checking.
(1) Receiver not operating :-
Examine AC power cord and plug.
Check fuse. If the
fuse has gone, there may be a short
circuit in the H . T . or heater circuits, o r failure of one
or more of the silicon diode rectifiers (D5, D6, D7 &
D8).
(2) No sound from speaker:-
Examine speaker connections, making sure that the
headphone plug is removed from the jack on the front
panel.
Check audio amplifier section by touching grid of V8
with a screwdriver.
Check detector stages.
AM --- detector diode (D4)
SSB --- BFO and product detector
(3) Audio and detector stages OK but receive fails to operate:-
In checking IF and RF stages make use of the "S" meter.
Examine the lst converter if the receiver fails only on
one band.
If click is apparent when grid of V3 is touched with a
screwdriver, fault is in the stages preceding V3.
Local oscillator injection voltage must be measured with
the VTVM.
NOTE - Dial Calibrations
On the main dial, the bottom scale is for 80 meters. "500"
represents 3 500 kHz, "600" represents 3 600 kHz, and so on.
The centre scale serves for the 40, 20 and 15 meter bands where
"0" represents 7 000, 14 000 or 21 000 kHz, "100" represents 7
100, 14 100 or 21 100 kHz, etc., depending on the band in use.