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5. Servicing RMX amplifiers
5.1 Mechanical disassembly and
re-assembly
Replacing components will usually require removing the channel
modules and/or AC board from the amplifier chassis, especially on the
RMX850 and RMX1450, which have single-side printed circuit
boards. The RMX2450 has double-side boards; many of the through-
hole components on the upper side of the board can be unsoldered
and soldered from the top side of the board, so removing modules or
boards is not always necessary.
See the fold-out assembly guides on pages 25 and 26 in this
manual for assistance.
NOTE: As viewed from the front of the amplifier, the left channel
module is Channel 1 and the right is Channel 2 except in the
RMX2450; its right module is Channel 1, and its left is Channel 2.
Removing the channel modules
1.
Disconnect the amplifier from AC power and allow at least 10
minutes for internal voltages to bleed down.
2.
Using a Philips screwdriver, remove the screws that fasten the
top cover to the chassis. Also remove the top cover's four
recessed screws that fasten it to the heat sinks. As you
remove screws, set them aside, but also make note of where
each type is used so you can properly re-assemble the
amplifier.
3.
Lift the top cover up at the rear and carefully pull it toward the
back, removing the five hooks on the front edge from their slots
in the chassis.
4.
Pull the gain control knobs straight off from the potentiom-
eter shafts.
5.
Tip the amplifier up on its side and remove the four screws
that fasten the heat sinks to the chassis.
6.
Set the amplifier back down and remove the screws that
mount the channel modules to the chassis standoffs. There
are six screws in the left module and five in the right one.
7.
Remove the four screws that fasten the fan, fan shroud, and
fan guard to the chassis. Lift the fan shroud out from the
chassis; this will give you room to properly remove the
modules from the chassis.
8.
Disconnect the wire and cable connections to the channel
modules. All of the connections are either detachable headers
or ¼-inch quick-connect tabs that are disconnected by pulling
them straight up. No unsoldering is necessary.
18
9.
Slide the channel modules toward the back so the potentiom-
eter shafts and front panel LEDs are clear of their holes in the
front panel. Lift the channel modules out from the chassis.
10. Re-assembly is the opposite of disassembly.
Removing the AC board
The AC board provides AC voltage selection, rectification of the
transformer secondary current, and a regulated DC supply for the
cooling fan. It seldom needs to be replaced unless it is physically
damaged itself. Most failures involving the AC board can be
repaired through replacement of individual components.
WARNING: Regulatory agencies require that any operating
voltage conversions from 120 volts to any other voltage be done
only by QSC's factory service. Any other operating voltage
conversions may be done only by a QSC-authorized service center
or international distributor.
1.
Disconnect the amplifier from AC power and allow at least 10
minutes for internal voltages to bleed down.
2.
Remove the four screws that fasten the fan, fan shroud, and
fan guard to the chassis. Lift the fan shroud out from the
chassis.
3.
Disconnect the wires that connect to the channel modules. All
of the large single wires attach to the channel modules with
¼-inch quick-connect tabs that are detached by pulling them
straight up. The remaining three black wires disconnect at the
left channel module with a detachable header.
If you are planning to replace the AC board with another,
carefully cut each of the transformer wires connecting to the
board just above its solder tab. You must leave enough slack
to allow connection to the new AC board. Remove the old
heat shrink tubing from the wires and strip the wire ends
about 0.25 inch or 6.3 mm.
4.
Remove the five screws that attach the AC board to the
chassis standoffs. Lift the board out from the chassis.
5.
Re-assembly is the opposite of disassembly. If you're using a
new AC board, slide new pieces of heat shrink tubing over the
transformer wires before you solder them to the appropriate
tabs on the board; after soldering, cover the joints with the
tubing and use a heat gun or other heat source to shrink them
tightly.
QSC Audio Products, LLC
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