Altec 1594B Operating Instructions Manual page 8

5.
Step Adjust R136 and R137 by one of the following
methods [method (a) i s preferred] :
Locate wire attached to terminal 1 of
output transformer T2. Connect
on milliammeter to this wire and adjust
R136 counterclockwise for a
rent of 40 mA.
milliammeter to wire attached to terminal
3 of output transformer T2 and adjust
R137 for a
Remove two screws securing Power Driver
PCB to chassis and lower PCB on hinged
connector.
across resistor R7 (see Figure
with highest scale t o protect meter. Ad-
just R136 for meter reading of 13 mV.
Change connection of millivoltmeter to
read across resistor R8 and adjust R137
for meter reading of 13 mV.
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
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
unscrewing fuse holder, replacing fuse and resecuring fuse
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 tLlrn
(see PARTS LIST), 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.
Remove four screws securing front panel. Open
Step 1.
and lower panel for access t o PCB (see Figure 5).
Remove two screws securing PCB to chassis
Step 2.
brackets.
Lower hinged connector of PCB and carefully
Step 3.
remove PCB from connector.
clamp.
a
cur-
Change connection of
"Q"
current of 40 mA.
Connect a millivoltmeter
Remove
re-
Step 4.
Carefully insert new or repaired power driver
PCB into connector. Do not warp, bend or twist
the board or conductor may fracture.
5.
Step Secure PCB with two screws removed in Step
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
points or PCB.
t i e
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
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.
Both sides of mica insulator are covered with silicone
3.
grease or fluid.
4. Mounting screws are tight,
Testing Transistors
Transistors should be checked with
tester i s not available, use the following procedure for test-
ing transistors with an ohmmeter.
Remove suspected transistor from circuit (see
Step 1.
Replacing PCB Components).
Connect ohmmeter leads to base and emitter.
2.
Step
Read on lowest ohms scale. Reverse leads and
read again. Normal readings should be
other.
Connect ohmmeter leads to base and collector.
Step 3.
Ohmmeter readings should be similar to those
obtained in Step 2.
2.
a transistor tester. I f a
a t least