Crest Audio 6001 Service Manual

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SSCRESIALJDIO

4601 Professional Power Amplifier

Clip/Limit 88mm
Signal

Temp/DC
Active

Professional Series
Power Amplifiers

3301
4601
4801
6001
7001

Service Manual

CREST AUDIO lNC., 100 Eisenhower Drive, Paramus, New Jersey 07652 USA
T (201) 909-8700 FAX (201) 909-8666

CREST AUDIO EU ROPE, 5a Wilbury Grove, Hove, East Sussex BN3 SJQ England
T44+(0)273-325840 FAX 44+(0)273~775462

CREST AUDIO ASlA., 6001 Beach Road #17-03, Golden Mile Tower, Singapore 0719
fi65+(0)295-2328 FAX 65+(0)295-47D7

Release 1.1 4/93 Domestic

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the user manual.

This symbol, a lightning flash with arrowhead within an equilateral triangle, appears on the
amplifier chassis to warn the user that uninsulated dangerous voltaggggge present within the
enclosure that may pose a risk of electric shock. "

This symbol, an exclamation point within an equilateral triangle, appears on the amplifier
chassis to warn the user to follow important operating procedures and precautions detailed in

This manual and the procedures detailed within are intended for qualified technicians
only! There are potentially lethal voltages present within an audio power amplifier, and it
is the responsibility of the technician to exercise common safety practices to protect him-

self, his co-workers, and the end user.

In particular, always exercise caution when working on an amplifier with the chassis
cover removed. Do not leave it unattended while it is connected to the Ac mains. Never
expose the amplifier or your test equipment to rain or moisture, and never work on an am-
plifier while you are standing in, sitting in or othenlvise in contact with, rain or moisture.
Before starting any repair or troubleshooting procedure, read and understand completely
the instructions for the procedure.

1 INTRODUCTION

#

This service manual includes tests, calibrations, schematics, a full parts list/order form, and troubleshoot-
ing tips to assist you in the repair and maintenance of Crest Audio Pro series 3301, 4601, 4801, 6001, and

7001 amplifiers.

The first step in troubleshooting is to identify the symptom. The next step is a complete visual inspection.
You may isolate the problem, trace it to a module, and swap it with a good module or continue trou-
bleshooting down to component level. If you follow this manual step-by-step it will be that easy. Good

luck!
Identify Visual Isolate Replace or
Symptoms Inspection Problem Troubleshoot

Glossary

Following is a list of terminology used in this manual.
Board A printed circuit board, or PCB.
Chassis The steel case or frame in which the modules, transformer, etc. are mounted.
Harness This term refers to all the wires, as a whole, which interconnect the boards carrying

specific voltages, signals etc.

Crest Audio Professional Series Power Amplifiers Page 1-1

Service Manual Release 1.1 4/93

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4TROUBLESHOOTING 8r REPAIRING THE
OUTPUT MODULES -er-

4.1 Visual inspection

Tools & materials needed:
M Phillips #1 and #2 screwdrivers

I/ Low or medium pressure compressed air, water vapor removed or compressed air in a can.
g I/ Short, medium-bristled artists or horsehair brush

1

V Methanol alcohol or a non-corrosive, non-lubricant solvent.

Setup:
I/ Amplifier disconnected from AC mains.

Procedure:

Remove all of the Phillips-head top cover screws. If the amplifier has a toroidal transformer, remove

the transformers upper mounting screw, which is the large Phillips-head screw toward the left side

of the top cover. Remove the top cover.

Note:_ Visual inspection is essential! Keep in mind that repairs may have been attempted by ,,
non-qualified persons. Also, debris may have entered the chassis through the ventihtion holes
during use.

Check for dirt and debris within the amplifier. If the fan filter is in place, make sure it is clean enough
to allow sufficient air flow; if necessary, wash the filter element with soap and water or, if

necessary, order Crest authorized replacement filters. Use compressed air (water vapor removed)

or compressed air in a can to clear dust from the heatsink fins and anywhere else in the amplifier
chassis.

Check for any type of conductive debris inside the amplifier chassis. Be thorough! A stray piece of
metal or wire can cause intermittent short circuits or even seriously damage components.

Check the wiring harnesses for broken or pinched wires, loose connectors, intermittent short circuits,
damaged insulation, etc.

Make sure the breaker/power switch, transformer, fan, and all modules and circuit boards are securely
mounted to the chassis.

Check for burn nmrks, especially on printed circuit boards. Ifyou find any, investigate the severity of
the damage. Using a short, medium-bristled artists or horsehair brush, carefully clean the area with
methanol alcohol or a non«corrosive, non-lubricant solvent. If a circuit board has a hole burned in

it or a foil trace lifted or destroyed, it must be replaced.

If the burn mark can be cleaned away and you find no damage to the printed circuit board, the board
need not be replaced; only the damaged components need to be replaced.

Crest Audio Professional Series Power Amplifiers Page 4-1
Service Manual Release 1.1 4/93

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7 Check the insulator underneath the transistor for rips, holes, or debris. Clear away anything that may
have caused a puncture in the insulator. :2;-

: 8 Replace the coolsil or mica. If a mica washer is used, coat both the heatsink area and the device with
a thin film of silicone thermal grease first.

9 Replace the transistors mounting screw. Tighten the mounting screws of the large power transistors
to 15 lb.-in (1.7 N-m). Over tightening will damage the mica and/or deform the coolsil insulator.
Carefully hand- tighten the mounting screws of the smaller devices enough to hold firmly without
crushing the shoulder washer, which would short the device to the heatsink. Replace the shoulder
washer if it is damaged. (Figure 5-7)

Step 10 is necessary because more than one transistor may be shorted to the heatsink

10 Repeat Steps 2 and 3 to test for voltage on the heatsink. Repeat this procedure as necessary until no
voltage remains on the heatsink.

Remember! There should be no DC, positive or negative voltage and no more than 10 volts AC
present on the heatsink with respect to chassis ground.

Tighten to 15 Ib-in
(1.7 N-m)

Hand tighten (do not crush 5 cu er washer)

an...

Figure 5-7. Transistor Mounts

; Crest Audio Professional Series Power Amplifiers Page 5-9
Service Manual Release 1.1 4/93