Ampex 351 - Page 87

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Troubleshooting the record amplifier
Trouble shooting the reproduce amplifier
8-14
ELECTRONIC
ASSEMBLY
Servicing and Repairing Printed Circuits
Because of the uniform wiring layout and
translucent boards, printed circuits can be
traced more easily than conventional circuits,
troubleshooting is less difficult, and any quali 
fied person will be able to service and repair
the equipment including replacement of com 
ponents by following the instructions, sugges 
tions and procedures in this section. The trans 
lucency of the board makes locating connec 
tions and test points easier if a light bulb is
placed underneath the circuit to be traced.
Continuity checks and measurement of resis 
tors, coils and some types of capacitors can be
made at the component side of the etched
board. Very small breaks in wiring can be lo 
cated by means of a magnifying glass. The
parts location illustrations and the schematic
diagram in this section can be used to advan 
tage when tracing circuitry, especially where
tube sockets are concerned. Pin numbers are
plainly marked.
Equipment and Tools Required
Diagonal cutters
Long-nosed pliers
Pocket knife
14-inch nut driver
Solder pick
Small wire brush
Pencil soldering iron
60/40 resin core solder
AUDIO
OSCILLATOR
Precautions
Be careful when removing components from
the board to avoid damaging the components
themselves or the copper foil wiring. If dam 
age occurs, small breaks can be joined with
solder, new foil can be cut to simulate the
damaged sections, and large breaks can be
repaired with hook-up wire. When applying
new foil, first remove all coatings such as flux,
grease and wax from the damaged portion and
place the adhesive side of the foil toward the
board. With the tip of the smooth wedge-
shaped soldering iron heat the new foil, sliding
the tip slowly along the copper surface for
about a minute to cure the bond.
Excessive pressure can crack the boards. Ac 
cess to certain components may not be possible
when the boards are in the chassis. To remove
the board from the chassis, remove the four
mounting nuts carefully. When disconnecting
the edge-on harness connectors, make certain
that the diagonal pliers grasping the individual
connector will not strike and break an adjacent
component. To prevent this type of damage,
insert a screw driver or similar protective de 
vice between the diagonal pliers and the vul 
nerable component. A vise with protected jaws
can be used to hold the boards while servicing.
Avoid excessive pressure against the boards
when using the vise.
Another source of damage can come from
overheating during the soldering process. Ex 
cessive heat can cause breaks in the bond be
tween the board and foil, necessitating costly
repair of the foil connections. Use 60/40 resin
core solder, the melting point of which is 375
degrees F. Some soldering irons are available
with tip temperature of 650 degrees F., but the
more skilled repair man can speed up the sold
ering process by using an iron with a tip temp 
erature in the neighborhood of 750 degrees F.
AUDIO
OSCILLATOR
89-0144
Issue A
T F
C ''r'REPRO
ion > HEAO
LOCATION POWER SUPPLY AND REPRO 
DUCE AMPLIFIER, and foldout SCHEMATIC
DIAGRAM — ELECTRONIC ASSEMBLIES).
Proceed as in troubleshooting the reproduce
amplifier. Typical voltage readings are shown
on the foldout schematic diagram. Using the
circuit below, check the record amplifier
against the appropriate response curve. Re 
move tube IV 6, and disconnect the record head
lead before checking amplifier response.
f- LINE TERM ON
/ OR NOMINAL 600 fl
I EXTERNAL LOAD
ELECTRONIC /
ASSEMBLY ifsjj
I TO 2 VOLTS
OUTPUT
REMOVE TUBE V6 IN BIAS OSCILLATOR
ANO DISCONNECT HEAD LEAD