Free Audio Service Manuals - Free download Fisher F 590 FUTURA Service Manual

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CAUTION: This is a FISHER precision high-fidelity in-
strument. It should be serviced only by qualified personnel -
trained in the repair of transistor equipment and printed circuitry.

EQUIPMENT AND TOOLS NEEDED
The following are needed to completely test and align this high-fidelity instrument.

Test Instruments

Vacuum-Tube Voltohmmeter DC VTVM

Audio (AC) Vacuum-Tube Voltmeter (AC VTVM)
Oscilloscope (Flat to 100 kc minimum)

Audio (Sine-wave) Generator

lnterrnodulation Analyzer

Sweep (FM) Generator (88 to 108 me)

Marker Generator

Multi lex Generator (prefeiably with RF output-
Fl HER Model 300 or equal).

Miscellaneous

AdlustableLineVoltage Transformer or
ine~voltage regulator

Load Resistors (2)-8-ohm, 50~watt (or higher)

Stereo source (Turntable with stereo cartridge
or Tape Deck)

Speakers (2) Full-range. for listening tests

Soldering iron (with small-diameter tip)
fully insulated from power line.

PRECAUTIONS

Many of the items below are included just as a re-
minder-they are normal procedures for experienced
technicians. Shortcuts can be taken but often they
cause additional damage-to transistors, circuit com-
ponents or the printed-circuit board.

Soldering-A well-tinned, hot, clean soldering iron tip
will make it easier to solder without damage to the
printed-circuit board or the many many circuit com
ponents mounted on it. It is not the wattage of the
iron that counts-it is the heat available at the tip.
Lowwattage soldering .irons will often take too long to
heat a connection-pigtail leads WI" get too hot and
damage the part. Too much heat, applied too long, will
damage the printed-circuit board. Some 50-watt irons
reach temperatures of 1.000'F-others will hardly
melt solder. Smalldiameter tips should be usedfor
single solder connections- larger pyramid and chisel
tips are needed for larger areas.

a When removing defective resistors, capacitors, etc.,
the leads should be cut as close to the body of the
circunt component as possible. (If the part is not being
returned for in-warranty factory replacement it may be
cut in half-with diagonal-cutting pliers-to make
removal easier.)

- Special desoldering tiplets are made for unsclder-
ing multiple-terminal units like IF transformers and
electrolytic capacitors. By unsoldering all terminals at
the same time the rt can be removed with little
chance of breaking t printedcircuit board.

I Always disconnect the chassis from the er line
when soldering. Turning the power switch FF is not
enough. Power-line leakage paths. through the heating
element. can destroy transistors.

Transistors-Never attempt to do any work on the
tran5istor amplifiers without ﬁrst disconnecting the
AC-power linecord-wait until the power supply filter-
capacitors have discharged.

- Guard against shorts-it takes only an instant for
a base-to-collector short to destroy that transistor and
possibl others direct-coupled to it. [In the time it
takes or a_ dropped machine screw. washer or even
the screwdriver, to glance off a pair of socket terminals
(or between a terminal and the chassis) a transistor
can be ruined.)

0 DO NOT bias the base of any transistor to. or near,
the same voltage applied to its collector.

0 DO NOT use _an ohmmeter for testing transistors.
The voltage applied through the test probes ma be
highertthan the baseemitter breakdown voltage 0 the
ran5is or.

Output Stage and Driver-Replacements for output
and driver tranSistors. if necessary,_ must be made from
the same. beta group as the original type. The beta
ﬁraoup is indicated by a colored dot on the mounting
meat the transistor. Be sure to include this irr
formation. when ordering replacement transistors.

O COWRlﬂH' was risen nnin cnnmwnmu an Dinn- Exam

0 If one output transistor burns out (open or shorts).
always remove all output transistors in that channel
and check the bias adjustment. the control and other
parts in the network with an ohmmeter before insert-
ing a new transistor. All out ut transistors in one
channel will be destroyed if t e base-biasing circuit
is open on the emitter end.

0 when mounting a replacement power transistor be
sure the bottom of the flange. the mica insulator and
the surface of the heat sink are free of foreign matter.
Dust and grit can prevent perfect contact. This re
duces heat transfer to the heat sink. Metallic particles
can puncture the insulator and cause shorts-mining
the transistor.

0 Silicone grease must be used between the transist-
or and the mica insulator and between the mica and
the heat sink for best heat conduction. Heat is the
greatest enemy of electronic equipment. It can shorten
the life of transistors. capacitors and resistors. (Use
Dow£orning 00-3 or 620194 or equivalent compounds
made for power transistor heat conduction.)

0 Use care when making connections to speakers and
output terminals. Any frayed wire ends can cause
shorts that may burn out the output transistors-they
are direct-coupled to the speakers. There is no output
transformer- nothing to limit current through the tran-
5istors except the fuses. To reduce the possibility of
shorts at the speakers, lugs should be used on the
exposed ends-at last the ends of the stranded wires
should be tinned to prevent frayed wire ends. The
current in the speakers and output circuitry is quite
high. Any poor contact or small-size wire, can cause

er losses in the speaker system. Use 14 or 16 AWG
or long runs of speaker-connecting wiring.

DC-Yoltnge Measurements-These basic tests of the
transistor Circuitry are made without the signal gener-
ator. Without any signal In t measure the circut volt-
ages-as Indicated on t e schematic. The voltage
difference between the base and the emitter should
be in the millivolt range-a sensitive Dc meter is
needed for these readings. A low-voltage range of lvolt,
full scale-or lower-is needed.

Audio-Voltage ( n) Measurements-The schematic
and printed-Circultiboard lalrout diagrams are used.
Input Signals are injected at he proper points~tound
most gwckly by usmg layout of the printedcircuit
board instead of the schematic. An AUDIO (AC) VTVM
connected to the test ints should indicate volta es
close to those values 5 own in the boxes on the sc e-
matic. Many of the signal levels in the input stages
are only a few millivolts-they can not be read on the
AC ranges stag/lied on most _Vacuum~Tube AC/DC Volt-
ohmmeters ( Ms). Even with a _1-volt range a signal
level of 100 millivolts (.1 volt) WI" be the first 1/10
of the meter scale. A reading of 1 millivolt (.001 volt)
will hardly even move the meter needle.

Fisher F 590 FUTURA Service Manual

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