DISMANTLING


UNIT BREAKDOWN

1. The receiver may be rapidly dismantled to eight sub-units as follows:-

(1) Front Panel

(a) Tuning escutcheon.

(b) Loudspeaker and escutcheon.

(c) Output level meter.


(2) Second Variable Frequency Oscillator

(a) Second v.f.o. (V12).


(3) First Variable Frequency Oscillator

(a) R.F. Amplifier (V3).

(b) First v.f.o. (V5).

(c) First Mixer (V7).


(4) 100 kc/s I.F. Amplifier

(a) Beat frequency oscillator (V19).

(b) Crystal Filter.

(c) L-C filter.

(d) First and second i.f. amplifiers (V14 and V16)

(e) A.V.C. and T.C. stages (V18)

(f) Detector and noise limiter (V21)

(g) 100 kc/s output (V17)


(5) Crystal Calibrator (V13 and V15)


(6) Main Chassis

(a) Aerial (antenna) attenuator.

(b) Crystal oscillator amplifier (V1).

(c) Harmonic generator (V2).

(d) 30 and 32 Mc/s low-pass filters.

(e) 37.5 and 40 Mc/s band-pass filters.

(f) Harmonic mixer (V4).

(g) The 37.5 Mc/s amplifiers (V6), (V8) and (V10).

(h) Second mixer (V9).

(i) A.F. output stages (V22) and (V23).


(7) 1.7 Mc/s oscillator/amplifier and mixer unit

(a) Second v.f.o. amplifier (V11).

(b) Third mixer (V25).

(c) Fourth mixer (V26).

(d) 1.7 Mc/s oscillator/amplifier (V27)


(8) 2-3 Mc/s Band-pass Filter



DISMANTLING AND RE-ASSEMBLY INSTRUCTIONS

2. Front Panel

(1) Remove all control knobs.

(2) Unscrew the eight instrument head panel fixing screws.

NOTE: The two screws at the bottom of the front panel,
adjacent to the jack sockets, are secured to the
main chassis with nuts.

(3) Carefully withdraw the front panel and unsolder the connections
to the meter and speaker switches; alternatively, the number
of wires to be unsoldered can be minimized (loudspeaker only)
by removing the seciring nuts on the SPEAKER and METER switches.
The panel may now be completely removed.

NOTE: When replacing the B.F.O. NOTE control knob, ensure
that the identification mark on the saft is uppermost
and that the pointer indicates zero when zero-beat is
obtained.

(4) Re-assemble in the reverse order.

NOTE: When removing the control knobs secured by a hexagon
collet insert the collet must be shot loose from the
spindle by a slight knock on the chromed centre of the
control knob.


SECOND VARIABLE FREQUENCY OSCILLATOR

3. (1) Remove the bottom cover.

(2) Unsolder the three connections on the 4-way tag strip, adjacent
to the terminal strip, situated in compartment 11 (see Fig.15:
Key to Under-chassis Layout).

(3) Remove the front panel: see para.2. above.

(4) Withdraw the Crystal Calibrator Unit by slackening the two
knurled nuts, disconnecting the coaxial cable and unplugging
the unit.

(5) Unbolt the cable cleat securing the dial light cable.

(6) Unclip the lampholder.

(7) Disconnect the coaxial cables.

(8) Remove the screws securing the Megacycles dial to the boss
and withdraw the dial.

NOTE: Do not unscrew the boss from the shaft. Unscrew the
two unit retaining screws on the top of the chassis
and one retaining screw from the underside of the
main chassis in compartment 11.

(9) The v.f.o. may now be withdraw vertically. When servicing
this assembly, clean the wormwheel and the split gear on
the ganged capacitor shaft with carbon-tetrachloride, then
apply with a brush, to the wormwheel only (Fig.11), a thin
coating of Molybdenum Disulphine grease (Rocol "Molypad").

(10) Re-assemble in the reverse order.


RENEWAL OF FILM TUNING SCALE

NOTE: Great care must be taken when feeding a new film into
position to avoid twisting or buckling.


REMOVAL

4. (1) Rotate the KILOCYCLES scale to the limit of its travel at
the 1000 kc/s end of the scale. Apply the scale lock.

(2) Remove the dial illuminating lamp and its holder.

(3) Hold the two gear wheels at the top of the right-hand film
bobbin against the spring tension and remove the two screws
securing the idler gear mounting assembly.

(4) Ease the idler gear clear of the film bobbin gear wheels
and carefully ease the spring tension from them. The film
bobbins are then free to revolve independently.

(5) Carefully lift the film clear of the tuning drive sprocket
and withdraw the film via the back of the loudspeaker.


FITTING A NEW FILM SCALE

5. (1) Carefully feed the low frequency end of the film scale via
the rear of the loudspeaker, the front of the tuning drive
sprocket and the front of the guide roller mounted between
the two right-hand film bobbins. Engage the prepared end
of the film in the right-hand bobbin. Slowly wind the film,
under very light tension, onto the bobbin until the STOP
marking is approximately in the centre of the escutcheon
window.

(2) Carefully feed the free end of the film via the rear of the
loudspeaker and the rear of the tuning drive sprocket.
Engage the prepared ond of the film in the left-hand film
bobbin. Slowly wind the film, under very light tension,
onto the bobbin until the sprocket holders in the film
engage with the tuning drive sprocket.

(3) Maintain the STOP marking approximately in the centre of
the escutcheon window and take up any slack in the film
by rotating the bobbins in opposite directions. When all
the slack has been taken up, rotate the gear wheels on
top of the bobbins a further 1/2 to 3/4 turn against the
spring tension and hold them in position. Refit the idler
gear wheel and mounting plate. Secure the mounting plate
screws and release the gear wheels.

(4) Check that the STOP marking is still approximately in the
centre of the escutcheon window.


SECOND V.F.O. VARIABLE CAPACITOR

NOTE: Refer to the v.f.o. alignment procedure in para. 24.
before attempting to refit the variable capacitor.

6. (1) Remove the second v.f.o. from the receiver in accordance
with the instructions in para.3. above.

(2) Unscrew the remaining cover plate.

(3) Unsolder the capacitor connections.

(4) Remove the drive gear and collet.

(5) Unscrew the four fixing screws holding the capacitor to the
bracket.

(6) Re-assemble in the receiver order, ensuring that the anti-
backlash gears are loaded.


FIRST VARIABLE FREQUENCY OSCILLATOR

7. (1) Remove the front panel, the bottom cover and the screens
from compartments 1, 6 and 8. (See Fig.15: Key to Under-
chassis Layout).

(2) Unsolder the connecting wires from the two turret lugs
situated in compartment 8, the leads to the turret lug in
compartement 6, the pin connections compartment 2 and the
screened cable compartment 1.

(3) Unscrew the three fixing screws on the top of the unit.


8. (1) Fitting a new chain:-

(a) Take a 63-link lenght of chain.

(b) Hold chain tension sprocket down towards the
chassis, and fit new chain round the two chain
wheels.

(c) Release the tension sprocket that ensuring that
it holds the chain under tension. See Front Panel
instructions refitting of B.F.O. control knob;
para.2. above.


100 KC/S I.F. AMPLIFIER

9. (1) Remove the left-hand gusset plate adjacent to the unit.

(2) Unsolder the leads to the 4 and 12-way tag strips (Fig.7)
and the 100 KC/S OUTPUT plugs.

(3) Disconnect the coaxial lead to the 1.7 Mc/s oscillator/
amplifier and mixer unit.

(4) Remove the six screws securing this unit to the main chassis.

NOTE: Removal of the R.F./I.F. GAIN control on the b.f.o.
assembly is necessary in order to obtain acces to
one of the six securing screws.

(5) Re-assemble in the reverse order.


BEAT FREQUENCY OSCILLATOR

10. (1) Remove Front Panel.

(2) Remove bottom cover.

(3) Disconnect leads from R.F./I.F. GAIN potentiometer.

(4) Remove side plates adjacent to i.f. amplifier.

(5) Remove screw securing cable cleat situated adjacent to
150mH choke assembly on underside of i.f. amplifier.

(6) Disconnect red-white lead of b.f.o. cableform from
terminal on adjacent 12-way tag strip.

(7) Withdraw red-white lead from cableform.

(8) Disconnect brown leads from pin 4 of V18 socket.

(9) Disconnect blue leads from pin 7 of V21 socket.

(10) Remove remaining three screws and crinckle washers to
release b.f.o. assembly from i.f. amplifier chassis.

(11) Re-assemble in the reverse order.


1.7 MC/S OSCILLATOR/AMPLIFIER AND MIXER UNIT

11. (1) Remove the bottom cover and the screen from compartment 7.

(2) Unsolder the two pin connections.

(3) Disconnect the coaxial cables.

(4) Remove the three screws securing this unit to the main
chassis.

(5) Re-assemble in the reverse order.


VALVE REPLACEMENT

12. With the exception of V5, replacement of valves will not affect
receiver alignment. When V5 is replaced refer to GENERAL SERVICING
AND ALIGNMENT PROCEDURES.


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