PIONEER QX-646 (01) PDF MANUAL

For playing a CD-4 disc record with an exclusive CD-4 phono cartridge, adjust channel separation between FRONT and REAR.

After this adjustment once made, with the CD-4 phono cartridge, 2-channel disc record reproduction is possible, too.

As far as reproduction of any stereo disc record with a 2-channel phono cartridge is concerned, always turn the LEFT and RIGHT knobs to central positions.

LEFT knob: Adjusts separation between FRONT (CH.1) and REAR (CH.2) for LEFT channel.

RIGHT knob: Adjusts separation between FRONT (CH.3) and REAR (CH.4) for RIGHT channel.

NOTE: Never fail to re-adjust the CD-4 SEPARATION CONTROL knohs whenever replacement with a new phono cartridge or stylus is made.

Turns the power on and off. Also controls the power to the SWITCHED auxiliary AC outlet on the rear panel.

SPEKR: Switches all speakers on and off. Button pushed OFF; button released ON. Use position OFF when listening through headphones.

REAR: Two pairs of rear speakers (pair A and pair B) can be connected and selected with this switch.

Button pushed – rear speakers B operating;

button released – rear speakers A operating.

NOTE: Always turn the VOLUME down to minimum before operating these speaker switches.

Accepts a pair of low impedance stereo headphones.

Only the front channels (front left and front right channels) are heard through the headphones.

Used for adjusting bass and treble.

Clockwise (counterclockwise) turning of these controls from the FLAT positions will boost (diminish) tone. Also, only the front (rear) channel can be adjusted by turning the front (rear) part while the other part is being held. For normal listening, set them to the FLAT positions.

For a more natural sound spectrum at low listening volume, push this button. Extreme low and very high sounds will be somewhat boosted. The loudness circuit acts on all four channels.

Push this button only when playing (or monitoring for a recording in progress) tapes with the tape deck connected to the TAPE MON and REC input or the REC/PB connector. In all other operation modes (PHONO, FM, AM, AUX), leave the button in off position, i.e. released. No sound is heard if this button is pushed when it shouldn’t be.

In released position, the FM muting circuit cancels out noise on unused FM signals (“inter-station noise”), but it also rejects very weak, faint FM stations. To receive such a station, push the button to turn off the FM muting circuit.

Controls the level balance of front speaker systems. Turning the control to the right (clockwise) from the center will decrease the sound of the left-side speaker systems, and turning it to the left (counterclockwise) will decrease the sound of the right-side speaker systems.

Controls the level balance between the speaker systems in front and rear speaker systems. Turning the control to the right (clockwise) from the center will decrease the sounds of the front-side speaker systems, and turning it to the left will decrease the sounds of the rear-side speaker systems.

Controls the level balance of rear speaker systems. Turning the control to the right (clockwise) from the center will decrease the sound of the left-side speaker systems, and turning it to the left (counterclockwise) will decrease the sound of the right-side speaker systems.

Controls the output volumes of all four channel signals simultaneously. Turning the knob to the right (the left) will increase (decrease) the volume.

This switch sets the desired mode; 2-channel stereo, matrix 4-channel, discrete 4-channel (CD-4).

2CH: Conventional 2-channel stereo reproduction. No sound is heard from the rear speaker systems.

4CH CD-4: For playing discrete 4-channel CD-4 records. Also for playing discrete 4-channel stereo programs such as reel-to-reel tapes and Quad 8 tape cartridges. Used for listening to 2-channel program sources, too. Sound heard from the left rear speaker (CH. 2) will be the same as that the from left front speaker (CH. 1), while sound from the right rear speaker (CH. 4) will be the same as that from the right front speaker (CH. 3).

RM: Used for 4-channel reproduction of RM (regular matrix) records, or FM stereo broadcasts playing RM matrix records. Also use this position when listening to 2-channel tapes, records and FM stereo broadcasts, adding 4-channel effects.

SQ: Used for 4-channel reproduction of SQ matrix record or FM stereo broadcasts playing SQ matrix records. Also use this position when listening to 2-channel records and FM stereo broadcasts, adding 4-channel effects.

This switch selects the program sources.

AM: For AM radio reception.

FM MONO: For FM monophonic reception only. Use this position only for receiving weak or noisy FM stations. Note that in this position FM stereo broadcasts will also be received in monophonic mode, even though the stereo indicator lights up.

FM AUTO: Usual FM reception, with automatic switching depending on whether the broadcast is stereophonic or monophonic.

PHONO: For record playing.

AUX: For playing signals fed to the AUX jacks.

a) Connect a 0.01µF capacitor between TP1 and ground before the alignment.

b) Connect a 220kΩ resistor in series with the vertical input terminal of the oscilloscope.

c) Remove the meter lead from terminal 18, then terminate a 4.7kΩ resistor between terminal 18 and ground.

d) Connect the vertical input to terminal 18.

e) Set the selector switch to FM MONO.

f) Connect the output lead of the sweep generator to the FM antenna terminals.

g) Set the output level of the sweep generator to 85dB.

h) Adjust the primary and secondary cores of T6 to obtain a symmetrical pattern.

i) Set the output level of the sweep generator to 65dB.

j) Adjust the cores of T4 and T5 for maximum gain and symmetry of the pattern.

k) Vary the output level of the sweep generator from 60dB to 90dB, then keep the top of the pattern flat and make sure that the center frequency does not drift. If it drifts, repeat steps (g) to (j).

l) Remove the capacitor (4.7µF) from terminal 28.

m) Disconnect the vertical input from terminal 18, then reconnect it to TP1.

n) Set the output level of the sweep generator to 70dB.

o) Observe the S-curve pattern when adjusting the cores of T7. (Linearity is improved by the primary core; symmetry by the secondary core).

p) Disconnect the 0.01µF capacitor from TP1 after the alignment has been completed.

q) Connect the capacitor (4.7µF) to terminal 28 after the alignment has been completed.

a) Turn the selector switch to AM.

b) Connect the output lead of the sweep generator to the AM antenna terminal.

c) Connect the vertical input of the oscilloscope to the TAPE REC jack.

d) Set the output level of the sweep generator to 40dB.

e) Adjust the IFT cores (T9, T10, T11) as shown in Fig. 6, for maximum gain and symmetrical pattern.

a) Turn the selector switch to FM MONO.

b) Connect the output leads of the FM signal generator to the FM antenna terminals.

c) Set the FM signal generator to modulation 400Hz, 100% and output level 12dB, frequency 90MHz; also the receiver dial at set 90MHz.

d) Connect the VTVM and oscilloscope (in parallel) to the TAPE REC jack.

e) Observing the output level on the VTVM, adjust the following cores for maximum reading on the meter.

T3 – Oscillator circuit

T1 – Antenna circuit

T2 – RF circuit

f) Set the frequency of the FM signal generator and the receiver dial to 106MHz.

g) Adjust as follows:

Trimmer capacitor CT3 – Oscillator circuit

Trimmer capacitor CT1 – Antenna circuit

Trimmer capacitor CT2 – RF circuit

h) Repeat steps (e) to (g) a few times.

i) Set the output level of the FM signal generator to maximum signal meter deflection.

j) Adjust the primary core of T7 for minimum sound distortion.

a) Turn the selector switch to AM.

b) Connect the AM signal generator to the AM antenna terminal.

c) Set the AM signal generator to modulation 400Hz, 30%, output level 30dB, frequency 600kHz. Set the receiver dial at 600kHz.

d) Connect the VTVM and oscilloscope (in parallel) to the TAPE REC jack.

e) Observing the output level on the VTVM, adjust the following cores for maximum reading.

T8 – Oscillator circuit

Ferrite loopstick antenna – Antenna circuit

f) Set the AM signal generator and the receiver dial to 1,400kHz.

g) Observing the output level on the VTVM, adjust the following trimmer capacitors for maximum reading.

CT5 – Oscillator circuit

CT4 – Antenna circuit

h) Repeat alignments (e) to (g) a few times.

i) After these alignments, lock the trimmer capacitor with paint.

a) Modulate the FM signal generator output by FM MPX modulator.

b) Turn the selector switch to FM AUTO.

c) Connect the FM signal generator to the FM antenna terminals.

d) Set the FM MPX modulator to modulation; main 1kHz (L + R) 100%, pilot 10%.

e) Set the output level of the FM singal generator to 60dB.

f) Turn the tuning knob to maximum reading on the signal meter.

g) Set the modulation of the FM MPX modulator to pilot only.

h) Connect the oscilloscope to TP2.

i) Adjust the transformers (T13, T14, T15) until the output level of the 19kHz becomes maximum on the scope.

j) Set the FM MPX modulator to pilot with L or R signal.

k) Connect the oscilloscope and VTVM to the TAPE REC jacks.

l) Adjust the semi-fixed potentiometer on the AF amp Ass’y (AWK-025) until the output level of the L or R signal becomes maximum on the scope.

a) Connect the FM signal generator to the FM antenna terminals.

b) Modulate the FM signal generator connected to the audio generator, check that the frequency response shows troughs at around 67kHz and 72kHz.

c) Should the item (b) give the unsatisfactory result, adjust T18 and T12.

a) Connect the FM signal generator to the FM antenna terminals.

b) Turn the selector switch to FM AUTO.

c) Modulate the FM signal generator connected to the FM MPX modulator, and set the FM MPX modulator pilot on. Check that the stereo indicator lamp goes in, then set the FM MPX modulator to pilot off, and check that the stereo indicator lamp goes out.

When IC SL60505 has been replaced, VR1 (VR10) must be re-adjusted. VR1 (VR10) controls the oscillation frequency of the phase locked loop demodulator.

The adjustment procedure described below is somewhat coarse but should yield satisfactory results even without measuring instruments if performed carefully.

Please note that the adjustment cannot be performed with a worn stylus or CD-4 record.

• REQUIRED INSTRUMENTS

New phono cartridge suitable for CD-4 tracking

New CD-4 test record (PQX-1011)

Oscilloscope

• PROCEDURE

a) Ground terminal No. 19 to defeat muting function.

b) Connect oscilloscope to terminal No. 14.

c) Turn carrier level control (on rear panel) to maximum.

d) Play band 1 of test record PQX-1011.

e) The oscilloscope shows a warble tone signal.

Turn back the carrier level control until a point can be found where the warble patter becomes deformed. Adjust VR10 so that the deformed waveforms grow changed into undeformed waves.

Repeat these steps several times.

f) Now connect oscilloscope to terminal No. 5.

g) Turn carrier level control to maximum again.

h) Play band 2 of test record PQX-1011.

i) Ajust VR1 in the same way as in step e, above.

a) Turn up volume to average listening level.

b) Play the Band 4 to adjust a 30kHz carrier level from the test record. “Signal For 30kHz Carrier Level Adjustment.”

c) Listening to the signal (400Hz), turn the Carrier Level Control knob of the QX-646 on the rear panel from the right (maximum position) to the left.

d) Turning the Carrier Level Control knob to the left, find the changing point of tone quality, at which the signal becomes distorted. Then turn to the right to let the knob adjust at a turning angle of between 15°~30°

Once the final carrier adjustment is made, the knob must not be turned except for readjustment after replacement of phono cartridge or stylus, and after a long period of play.

1. Set the tuning capacitor to maximum capacitance.

2. Tie one end of the string to the hook on the side of the tuning pulley, then lead it to the arrow-indicated direction shown in the figure.

3. Wind the string 1/2 turn around the tuning pulley, then lead it to the small pulleys A, B, and C in order.

4. Wind the string 3 turns around the tuning shaft, then lead it to the small pulleys D and E.

5. Lead the string to the small pulley F, then wind it 2 turns around the tuning pulley.

6. Finally, tie the end of the string to the spring on the tuning pulley.

7. Tune receiver to low end. Fasten dial pointer to string so that it indicates low end on dial scale.