Step
5.
Adjust
and R137 by one of the following
methods [method
i s preferred] :
Locate wire attached to terminal
of
output transformer
Connect a clamp.
on milliammeter to this wire and adjust
R136 counterclockwise for a
cur-
rent of 40
Change connection of
milliammeter to wire attached to terminal
3
of output transformer
and adjust
R137 for a
"Q"
current of 40
Remove two screws securing Power Driver
PCB to chassis and lower PCB on hinged
connector.
Connect a
across resistor R7 (see Figure
with highest scale t o protect meter. Ad-
just
for meter reading of 13
Change connection of millivoltmeter to
read across resistor
and adjust R137
for meter reading of 13
Remove
millivoltmeter and secure PCB to chassis
with two screws previously removed.
Step 6.
Close front panel and secure with four screws
removed in Step 2.
ASSEMBLY REPLACEMENTS
Fuses
Step 4.
Carefully insert new or repaired power driver
PCB into connector. Do not warp, bend or twist
the board or conductor may fracture.
Step
5.
Secure PCB with two screws removed in Step
2.
Step 6.
Perform ADJUSTMENT OF POWER DRIVER
BALANCE CONTROL procedure.
RECOMMENDED SERVICE TECHNIQUES
I f systematic troubleshooting shows need for parts replace-
ment, observe the following precautions.
Transistor Orientation
Solid-state components are packaged in various case sizes
and types with various lead orientations (see Figure
9).
Be-
fore removing a solid-state component from tie points or
from a PCB, sketch the lead orientation with respect to the
t i e
points or PCB.
Form the leads of the new component to conform with the
leads of the part being replaced to aid in making proper
connections. Before removing small transistors, note posi-
tion of index tab with respect to the PCB or socket. Cut
the leads of the new transistor to the required length and
insert them, properly indexed, into the PCB or socket.
Replacing Power Transistors
The ac primary power fuse i s mounted on the front panel
(see
cover photo). The battery power fuse is located on the
rear of the chassis (see Figure 6). I f fuse replacement i s re-
quired, determine and correct any cause of failure before
re-
fuse. Install an identical fuse (see PARTS LIST) by
unscrewing fuse holder, replacing fuse and resecuring
holder.
Pilot Lamp
The pilot lamp i s located on the front panel (see cover
photo). I f replacement
is
required, unscrew the red pilot
lamp shield to expose the bulb. Press bulb inward and
remove. Install an identical bulb
(see
PARTS
then replace red pilot-lamp shield.
Power Driver PCB
I f the amplifier fails because of
a
faulty power driver PCB.
operation may be restored by replacing the PCB with
a
new
or repaired PCB. Use the following procedure.
Step 1.
Remove four screws securing front panel. Open
and lower panel for access t o PCB (see Figure 5).
Step
2.
Remove
screws securing PCB to chassis
brackets.
Step 3.
Lower hinged connector of PCB and carefully
remove PCB from connector.
Verify the following conditions exist when replacing
power transistors.
1.
Mica insulator i s not damaged. I f damaged, use new
insulator.
No grit or metal particles are between transistor and
heat sink.
3.
Both sides of mica insulator are covered with silicone
grease or fluid.
4.
Mounting screws are tight,
Testing Transistors
Transistors should be checked with a transistor tester. I f a
tester i s not available, use the following procedure for test-
ing transistors with an ohmmeter.
Step
Remove suspected transistor from circuit
Replacing PCB Components).
Step
2.
Connect ohmmeter leads to base and emitter.
Read on lowest ohms scale. Reverse leads and
read again. Normal readings should be a t least
times greater in one direction than in the
other.
Step
Connect ohmmeter leads to base and collector.
Ohmmeter readings should be similar to those
obtained in Step 2.
