Yaesu FT-901DM Maintenance Service Manual page 54

is amplified by Q2g0s and Qog96 (both JF-1033B)
and Q2g07 (2SC372Y), and fed through a diode
switch to the PLL UNIT (replacing the VFO
signal).
Qzsi3 (SN74LSOON) and Q3s;3 (SN74LS04N)
generate timing pulses to set or reset the counter.
The 200 Hz signal delivered from Q>3,, is ampli-
fied by Qzg80s (MPSA13) and rectified by Dogo4
and D2go95 (both 1S188FM) to produce a minus
voltage to be used for operational amplifier Qo329-
POWER SUPPLY
The power supply is designed to operate from
either 100/110/117/200/220/234 Volts AC 50/
60 Hz (all models) or 13.5 Volts DC with the
DC-DC converter unit (built-in on the FT-901DM,
optional on other models). Insertion of the ap-
propriate power plug into the rear panel receptacle
makes the necessary connections for operation
from either AC or DC power sources.
When the transceiver is operated from a 13.5 Volt
DC power source, transistors Q329; and Q3202
(both T20A6) function as a low frequency oscil-
lator to provide AC voltage at approximately 80
Hz to the power transformer. All of the tube
heaters receive their power through the HEATER
switch on the front panel. With the HEATER
switch in the OFF position, voltage is still supplied
to the receiver section, thus allowing continuous
reception with reduced power consumption. The
heaters of the two 6146B are connected in series to
operate at 12 Volts DC.
(1) Low voltage supply
AC 11.5 Volt power delivered from the secondary
winding of the transformer is rectified by Dy 001
and Dyo02 (V06B) in the RECTIFIER A UNIT
(PB-1708) to provide the transistor supply voltage.
The rectified DC voltage is supplied through pin
8 and pin | of the AC plug to pin 1 of the power
receptacle which is connected to the DC power
supply line. In the DC mode, the DC voltage from
the power cord is directly supplied to pin 1 of
the power receptacle. The DC voltage is filtered
through CHj901, C1001, and Cjo902, and fed to
the voltage stabilizer Q, (uPC14308) (8V) and
Q3 (uPC14312) (+12V); 13.5 Volt power is also
TECHNICAL NOTES
supplied to the counter unit and accessory socket
on the rear panel.
The stabilized 8 Volt supply from Q, is used for
the VCO, XTAL and IF UNITS, and the stabilized
12 Volt supply is used for the FM, VOX, and AF
UNITS, and other circuits as well. The 12 Volt
supply is further stabilized by Q, (uPC14308) to
be supplied to the AF and IF UNITS. A further
portion of the 8 Volt supply from Q, is stabilized
at 6 Volts by Qis0: (TA7089M) to be supplied
to the VFO UNIT.
Independent voltage stabilizers are located in the
MEMORY, COUNTER, AF, FM, and PLL UNITS.
(2) High voltage supply
The power amplifier plate voltage of +800 Volts
DC is supplied from the bridge-controlled doubler
RECTIFIER UNIT B consisting of Dy4o; - Diara
(10D10) and Cy59; and Cy5o2 in PB-1712.
AC 190 Volts is rectified by Djgo2 (10D10) in
RECTIFIER UNIT C to obtain 210 Volts-for the
screen grid supply of the power amplifier tubes.
The screen grid voltage is reduced to 180 Volts
for the FM, AM, and FSK modes.
The plate supply for the driver tube is obtained
by rectifying 250 Volt AC by Djg0; (10D10).
The DC voltage obtained from the RECTIFIER
C UNIT is dropped to 160 Volts by a resistor for
the driver screen grid.
120 Volt AC from the transformer secondary
winding is rectified by Dj,oo4 (10D10) in the
RECTIFIER A UNIT (PB-1708) to obtain -140
Volts for the grid bias voltage for the driver and
final amplifier tubes.
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