Fisher SR 110 Service Manual

Page 2

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TEST EQUIPMENT and SERVICE TIPS

The Following equipment is required to repair, calibrate and adjust the SR-110 Tape Deck.

Line Voltage Autotransformer or Voltage Regulator

DC Vacuum Tube Voltohmmeter

Accurately Calibrated AC Vacuum Tube Voltmeter
Frequency Counter (200 KHZ) or Oscilloscope and Low
Distortion Audio (Sine Wave) Generator (110 KHz or
more)

0 Azimuth adjustment cassette tape such as BASF 455-3,
TEAC 116L or equivalent (10 KHz recording @ ~zero,
-10, or -20 dB)

000.

O Takeup, Rewind tension checking cassette, Robins
R36004 (Robins Industries, Commack, N.Y. 11725) or
equivalent
Q-tips and alcohol (rubbing or wood)
Light machine oil such as Singer sewing machine oil
Lubricating grease such as Lubriplate
Tension Gauges:

II) Zero to 100 grams

(2) Zero to 700 grams (or Zero to 25 or more ounces)

UTI o . This precision highvfidelity instrument should be serviced only by qualified personnel,
CA N ' trained in the repair of transistor equipment and printed circuitry.

ELECTRICAL CHARACTERISTICS

Bias and Erase Frequency
Bias Currant

Erase Current
Microphone Sensitivity

AUX Sensitivity

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 solders
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 maybe 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 ale-soldering tips made
especially for this purpose. Removing solder from terminals,
reduces the pass ility 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 basa-to-collactor
short to destroy a transistor (and others direct-coupled to it).
In the time it takes for a dropped screw, washer, or screw-

105 KM: i 5 KM:

G V across RIP Head

IVTVM only)

20 V across Erase Head

0.2 mV for Zero VU on

recording meters, 1 volt at LINE OUT

100 mV for Zero VU, 1 volt at LINE OUT.

driver, to contact a pair of terminals lor terminal and chassis),
a transistor can be ruined.

SOLID-STATE DEVICES: integrated Circuits contain the
equivalent of many circuit parts, including transistors, diodes,
resistors, and capacitors. The preferred troubleshooting pr0<
cedure requires isolating the trouble to one stage using AC
signal tracing methods. Once the suspected stage is located
the DC voltages 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. Forward 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 Ieadsare
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 da»
stroy the junctionls) within the device.

VOLTAGE MEASUREMENTS: All voltages are measured
with the line voltage adjusted to 120 volts. All measured
voltages are t 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 1974 FISHER RADIO 0 All Rights Reserved.

Page 7

INTERCONNEOTIONS TOP (CONTROL PANEL)

T0
Pou
TO PIN 5
ON $25.30
To PIN 5
, ON Its. an BLK-WHT
War
To mm F2
F°°2 PM 0,351: PILOT L|GHT
TERMINAL BD
wm
ND
TO
P009
. To PIN I2
TO pm 13
T0 pun war
on as an
; PNK
T0 PIN 2 GRNBLK
To PIN I5

TO Pm!

TO FIN l4
_ TO
3 P014
L TO PIN 8
TD
P016 TO PIN 9

WHT-ELK

AL4055-Irs-4
T V SR-HO TOP CONTROL PANEL INTERCONNECTIONS