Led Checks - Crown Macro-Tech MA-5002VZ Service Manual

MA-5002VZ Service Manual
partial, if not complete, repair before power is ever ap-
plied. These checks are designed to find problems in
the output stages. The ultimate guide should always be
common sense.
To access all of the modules, simply remove the top
cover, rear panel, and bottom cover. The main module
will slide up and back for access to output module com-
ponents by loosening four screws. The main module
tray need not be removed in order to remove an output
assembly, however, to perform component replacement
on the main module the tray should be removed com-
pletely and the module removed from the tray. Note that
the current sense module is actually comprised of two
separate boards, connected by dual ribbon cables,
hardwired at both ends. The smaller board is called
current sense, the larger is, by itself, referred to as the
terminator. Either name, however, may be applied to
the pair. In Section 8 they are covered as a single part,
D 7994-3.
a.) Locate the flyback diodes D506, D507,
D508, and D509 on the emitter modules and check for
indications of a short. If a short is indicated, this means
that an output device or driver transistor in parallel with
that diode is shorted, usually not the diode itself. If a
faulty output device is found, the entire output assem-
bly may be replaced, or only the affected components.
If an output device is found to be defective, emitter re-
sistors should also be checked. If no output device is
found defective, perform a quick check of driver, pre-
driver, and bias transistors. Then, if no problem is found,
move to power-on checks.
b.) Check driver and pre-driver transistors for
shorts or opens. If a fault is found, do an in-circuit static
check of all semiconductors on the output modules. If
no output device and nothing upstream is found defec-
tive, move to power-on checks. Otherwise continue.
c.) If a failure has occurred anywhere in the
output stages, check bias servo transistors on each
(positive and negative) output module. Any failure as-
sociated with bias transistors may result in repeat fail-
ure of the affected channel even if all other defective
components have been found and replaced.
5-2 Maintenance
d.) If a failure is found in any LVAs, checks
should continue up onto the main module in the volt-
age translator stage.
e.) Failure within the power supply itself is very
rare, however a cursory check of major items is always
prudent. A 30A fuse should not blow unless a cata-
strophic failure has occurred in the output stage or
power supply. The low voltage fuse should not blow
unless a failure has occurred, probably in the supply
itself. If a failure has occurred in the output stages, check
the MOSFET switches and other VZ control components,
such as bridge rectifiers.

5.3.2 LED Checks

When power-off checks are complete and any defects
found are corrected during that phase, the next step is
to apply power. The MA-5002VZ includes several LED
indicators to assist you in troubleshooting an amplifier
malfunction.
All indicators on the amplifier, both front panel and in-
ternal, are important. External indicators include Enable,
ODEP, SPI/IOC, and I
LOAD
clude DC/LF, Fault (output module), Standby, and Over-
voltage/Transformer Thermal.
A chart on the following pages lists likely LED combina-
tions and likely causes. In each case it is assumed that
the LED circuit itself is operating properly. If a failure is
suspected, compare amplifier indicators with the chart.
In order to ensure that the problems are assessed cor-
rectly, perform the LED checks under the following con-
ditions: Before power is applied, ensure that the Ste-
reo/Mono switch is in the STEREO position. Do NOT
connect any signal source or load to the amplifier. Turn
the amplifier on. After approximately 4 seconds the turn-
on delay should time out. During the delay, IOC indica-
tors will usually be on and ODEP indicators should be
off. After the delay times out, relays click on, IOC indi-
cation should go off, and ODEP indicators should come
on. If this does not occur, definitely refer to the chart
that follows. Although this chart contains most likely fail-
ures, it does not cover every possibility. Common sense
and a study of schematics and circuit theory (provided
in Section 4) should ultimately lead to a proper repair.
130446-1 Rev. A
/I . Internal indicators in-
LIMIT
©2000 Crown International, Inc.