Fisher 504 Service Manual

Page 2

CONTENTS and SERVICE TIPS

REQUIRED TEST EQUIPMENT
MECHANICAL DISASSEMBLY
HARMONIC DISTORTION TEST
DIAL STRINGING
SIGNAL FLOW
CHASSIS LAYOUT
TUNER
IC DESCRIPTIONS
ALIGNMENT
AM DYNAMIC NOISE LIMITER 10
SELECTOR SWITCH 10
PREAMPLIFIER 10

mucosa-prowess

CONTROL AMPLIFIER 12
MODE/MONITOR SWITCH 13
SO DECODER 14

SO DESCRIPTION 14
SWITCH BOARDS 16
MASTER BALANCE/VOLUME 17
POWER AMPLIFIER 18

ADJUSTMENT 18

CIRCUIT DESCRIPTION 19
SPEAKERS SWITCH 20
AUDIO DISPLAY/PHONES 20
POWER SUPPLY 22

CAUTI o N. This precision high-fidelity instrument should be serviced only by qualified personnel,
I trained in the repair of transistor equipment and printed circuitry.

Many of these items are included only as a reminder - they
are normal procedures for experienced technicians. Shortcuts
may be taken, but these often cause additional damage to
transistors, circuit components, or printed circuit boards.

SOLDERING: A well-tinned, hot, clean soldering iron tip
will make soldering easier, without causing damage to the
printed circuit board or the components mounted on it.
Regular use of a sponge cleaner will maintain a clean
soldering surface. The heat available at the tip. (not the watt-
age of the iron) is important. Some 50-watt irons reach tem-
peratures of 1,0000 F, while others will hardly melt solder.
Small-diameter tips should be used for single solder con-
nections, pyramid and chisel tips for large areas.

Always disconnect the AC power cord from the line when
soldering. Turning the power switch OFF is not sufficient.
Power-line leakage paths, through the heating elements of the
iron, may destroy transistors.

PARTS REMOVAL: If a part is not being returned for in-
warranty factory replacement, it may be cut in half (with
diagonal cutting pliers) to make removal easier. Multiple
terminal parts. such as IF transformers, or electrolytic capaci-
tors, should be removed using special de-soldering tips made
especially for this purpose. Removing solder from terminals,
reduces the possibility of breaking the printed circuit board
when the part is removed.

ACCIDENTAL SHORTS: A clean working area, free of metal
particles, screws, etc., is an important preventive in avoiding
servicing problems: Screws, removed from the chassis during
servicing, should be stored in a box until needed. While a set
is operating, it takes only an instant for a base-to-oollector
short to destroy a transistor (and others direct-coupled to itl.
In the time it takes for a dropped screw, washer, or screw-
driver, to contact a pair of terminals (or terminal and chassis),
a transistor can be ruined.

SOLID-STATE DEVICES: Integrated Circuim contain the
equivalent of many circuit parts, including transistors, diodes,
resistors, and capacitors. The preferred troubleshooting pro-
cedure requires isolating the trouble to one stage using AC
signal tracing methods. Once the suspected stage is located
the DCvoltages at the input and output leads are measured to
give an accurate indication of the operating conditions of the
IC. DO NOT use an ohmmeter, to check continuity with the
IC mounted on the printed circuit board. Fonuard biasing the
internal junctions within the IC may burn out the transistors.
Do not replace a defective IC until all external resistors,
capacitors, and transformers are checked first, to prevent the
replacement IC from failing immediately due to a defect in
the connecting components. Solder and unsolder each lead
separately using a pliers or other heat sink on the lead to

prevent damage from excessive heat. Check that the leads are
connected to the correct locations on the printed circuit
board before turning the set on.

Whenever possible, a transistor tester should be used to de-
termine the condition of a transistor or diode. Ohmmeter
checks do not provide conclusive data, and many even de-
stroy the iunction(s) within the device.

Never attempt to repair a transistor power amplifier module
until the power supply filter-capacitors are fully discharged.

If an output or driver transistor becomes defective (opens or
shorts), always check ALL direct-coupled transistors and
diodes in that channel. In addition, check the bias pet, and
other parts in the bias network, before installing replacement
transistors. All output and driver transistors in one channel
may be destroyed if the bias network is defective. After parts
replacement, check bias for specified idling current.

In some applications,..replace_rnent of transistors must be
made from the same beta group' as the original type. The
beta group is indicated by acolored marking on the transistor.
Include this information when ordering replacements.

When mounting a replacement power transistor, be sure the
bottom of the flange, mica insulator, and the surface of the
heat sink, are free of foreign matter. Dust and grit will pre-
vent flat contact, reducing heat transfer to the heat sink.
Metallic particles can puncture the insulator, cause a short.
and destroy the transistor.

Silicone grease must he used between the transistor and the
mica insulator and between the mica and the heat sink for
best heat transfer. Use Dow-Corning DC-S. or an equivalent
compound made for power transistor heat conduction.

Use care when making connections to speakers and output
terminals. To reduce the possibility of shorts, lugs should be
used on the exposed ends, or stranded wire should be tinned
to prevent frayed wire ends. Current in the speakers and out-
put circuitry is quite high - poor contacts, or small wire,
can cause significant power losses. For wire lengths greater
than 30 feet, 16 AWG, or heavier, should be used.

VOLTAGE MEASUREMENTS: All voltages are measured
with the line voltage adjusted to 120 volts. All measured
voltages are 1 20%. DC voltages are measured to chassis
with a VTVM, with no signal input unless otherwise noted.
AC signal voltages are measured under the conditions speci-
fied on the schematic.

ALIGNMENT PROCEDURES: DO NOT attempt realignment
unless the required test equipment is available, and the align-
ment procedure is thoroughly understood.

© COPYRIGHT 1973 FISHER RADIO - All Rights Reserved.

Page 9

TUNER ALIGNMENT

erator 19,000 Hz pilot
output.

ITEM GENERATOR DIAL SETTING INDICATOR PROCEDURE
9. MPX OSC Set to position of non- Tune to generator, Connect frequency Adjust R554 for indication
ADJUSTMENT interference, with CW Release FM MUTING counter to Tp 72_ of 19,000 Hz (:50 Hz).
output of 2 mV. OFF pushbutton.
ALTERNATE Sat to position of non- Tune to generator. Scope vert input 0 Tp Adjust R554 for stable
MPX osc interference, with CW Release FM MUTlNG 72 through 22K. Scope Lissajou display as shown
ADJUSTMENT output of 2 mV. OFF pushbutton. hor input to MPX gen. in MPX 050 response

10. 38 kHz TRAP
ADJUSTMENT

Scope vert input to

Scope nor input to
MPX generator
19,000 Hz pilot
output.

audio oscillator output.

Adjust osc frequency for
stable 2:1 Lissaiou display
(38,000 Hzl.

Note: Do not change osc
frequency; proceed with
38 kHz trap adjustment.

11.

Modulate generator with
38,000 Hz, :75 kHz
deviation, Set generator
output to 2 mV.

Tune to generator. AC VTVM and scope
vert input to OUT TO
RCDR FRONT LEFT
jack, another AC
VTVM and scope to

FRONT RIGHT lack.

Adjust 2504 and 2505
for minimum ltvpically
more than 40 dB below
audio level).

AM ALIGNMENT - AUDIO DISPLAY and AM DNL depressed, TONE CONTROLS and MASTER BALANCE to center. SPEAKERS to
PHONES ONLV, MODE/MONITOR to STEREO, SELECTOR to AM, MASTER VOLUME to MIN.

Maintain generator output as low as possible for suitable indication

ITEM GENERATOR DIAL SETTING INDICATOR PROCEDURE
1, u: 455 kHz sweep generator Position of non- Scope vert Input to Connect a jumper between
ALIGNMENT to pin 70, 9nd to pin 5X. interference near pin 61, 9nd to pin 5X. pin 67 and pin 52. Adjust
Use 0.1 uF capacitor in 1400 kHz. Z304, Z303, 2302 top
series with generator lead, and bottom slugs for max
gain and best symmetry.
Keep signal low enough for
noise on response as shown
in AM lF, Disconnect
jumpert
2. FRONT AM generator to EXT AM Center of 600 kHz Front panel signal Adjust 2301 and L300
END ANT and GND terminals. calibration mark on meter, M1. lantenna) for max
ALIGNMENT Open GND link. Set to dial. deflection. Reduce
600 kHz. Modulate with generator output to keep
400 Hz, 30% modulation. panel meter at aporox 3.
3. Set to 1400 kHz. Center of 1400 kHz Front panel signal Adjust C304 and C302 for

calibration mark on
dial.

meter, M1.

max deflection. Keep
meter at approx 3.
Repeat steps 2 and 3
for max signal and
accurate dial calibratlon.

6

+5) @

COOOOOOOOOOOOO.

Q

58

FM
DETECTOR

@

@

2504
(L 33H
TRAP)

Z505
(R 35 kHz
TRAP)

©®

2503
0.7 MHII
OUADRATURE
ADJUST

l9kHz

R55
6 22K

TP72

R554
MPX OSC
ADJUST

@

(9

FM lF

AM IF

<9 M :)§w§§§' @ @ ®

©

2502
FM IF
0.7 MHzI
25m
FM ANT
L503
FM MIXER
2303
(455 kHz)
@ c5l7
FM MIXER
6514
FM 05¢
70
ZSOI
OJUF AM osc
455kHz
SWEEP @
1304
(455 Hill 2302 57
(455 kHz) JUMPER
52

5X

(.9 6

©©Q

NOTEZCHASSIS GROUNDS ARE COMPLETED THROUGH MOUNTING SCREWS (93). TIGHTEN BEFORE ATTEMPTING ALIGNMENT.

FM
DETECTOR

, . T t l t.
EQUALINDBSE ; mt infantile; »

SYMMETRICAL
TUNING

AL230I-l77 304. 404, 504

4 ._ lOkHz

Page 23

Sun. ._ ,r . , -~ ,_ . sul-
Symbol Description Part Number R01. Symbol Dmviption ' Parf Number Rat.
C901 Ceremic, 330pF, +ao-20% CK22352-3 .40 J1 Ac Outlet JK20665 .60
' - c901 Ceramic, anopF, 4ODVAC 0511544 .90 L901 Choke. 0.55UH L021818 .45
0902,9011, Ceramic, 0.021JF, 20%, 500v 01(223593 .45 0901 Transistor. PNP TR02062-6 3.20
904, 905, 0902, 90:1 Transistor, NPN TR01045 3.05
905, 909 15901 Composition, 920K, 10% nc205F824K .30
0905,5107 Electrolytic, BOOOUF, 50v 05223572 7.10 R902, 90:1 Deposited Film, 220 Hsooczzu .35
0910 Electrolytic, 4101.1F, 100v 052234344 .90 R904 Wirewound, 0.51, 2w nw200w1=1511 .60
0911 Electrolytic, 1000UF,50V 052234336 1.25 R905 Wirawaund, 150, 10w RF10W151J .50
0912 Ceremic, 0.01UF, +80-2096, 100v C503570-1 .40 R906 Wirewound, 100, 2w RW200W101J .45
c913 Electrolytic, 470uF, 50v 052234333 .95 11907 Deposited Film, 22K BsoDczzaJ .30
c914 Electrolytic, 100UF, 100v 0522343-43 .75 R908 Wirewound, 150, 5w RP5W151J .50
C915 Electrolytic, 100UF. 25v C522343-26 .45 11909 Deposited Film, 690 R50DC681J .35
C916 Myler, 0.1UF, 20%, 250v 05035754 .50 11910 Deposited Film, 47K RsoDc47aJ .30
C917 Mylar, 0.22UF, 109a, 250v C503575»2 .60 R911 Deposited Film, 10K HsoDcmaJ .30
CR901A,B, Bridge Rectifier, 25A, 200v 915514012 8.00 11912 Composition, 510 Rc209F51 1.1 .30
c, D 11913 Composition, «7 RCZOBF47DJ .30
CR902A, 13, Bridge Rectifier. 1.5A, 200v 311514001 1.45 H914 Wirewound, 101:1, 3w awswwu .50
c, D 51 Switch, POWER 595020065 2.95
CR903A Zener. 20v, 3%, 1w TR14002-13 1.25 '91 Switch, POWER SP50200«64 2.55
CR9035 Zener, 15v, 3%, 1w 112140024: 1.25 '52 Switch, Fused Voltage Selector 511513044 1.90
cR904 Zener, 24v, 5%, 3w TR 14001-1 1.05 T1 Trenslormer, Power TD4094-115 36.70 -
F901 Fuse, 6A, 125v, Sla-Blo F 1.51313-25 .70 - 1'1 Trenslormer, Power TE4094-215 '-41.
901 Fuse, 5.34., 250v,51o-Blo F51 3247-24 .60 - . Line Cord w50023-1 1.20
F901 Fuse, 3.15A, 250v, 510-an F510247-20 .60 - . Liue Cord (3-Conductor) w920678 3.20
F902, 903 Fuse, 10A, 250v, SIo-Blo FL51313-22 .85 - » Mounting Pad, 0901 Asosia .40
F904 Fuse, 3/44, 250v, Slo-Blo FL51313-7 .95 - 5 Heat Sink, 0901 A509942-5 .50
11, 2, 3, 4 Dlal Lamp LM21434 1.00 - - Insulator, 0.902, 090:1 520413-11 .25
15, 6 Lernp, Meter-Signal, Center»of

'Used in Export Unns

Except as noted, resisturs are 5%, ysw. K=Kllohm