Servicing Rmx Amplifiers; Mechanical Disassembly And Re-Assembly - QSC RMX 850 Technical & Service Manual

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 RMX 850
and RMX 1450, which have single-side printed circuit boards. The RMX 2450 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 RMX 2450; 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 potentiometer 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.
9. Slide the channel modules toward the back so the potentiometer 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 trans-
former 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.
14 QSC Audio Products, Inc.