©2001 Marchand Electronics Inc. PO Box 473 Webster NY 14580 (585)872 0980 www.marchandelec.com
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sockethead screws and the handles. Use lockwashers
with these screws. Install the fifth screw in the bottom
of the panel. Use a 6/32 black flathead with kepsnut
for this.
Feet:
Install the 4 rubber feet in the bottom of the
cabinet using the #6 selftap screws.
Transformer:
Install the transformer. See figure
below.
PS112 Power supply:
Install the power supply next
to the power transformer using 5 hex 1/2" standoffs,
as shown in fig x. Use 6/32 x 3/8 flatheads on the
bottom and 6/32 x 1/4" panheads on top.
MB401 power amplifier board:
Install the board onto
the heatsink with the 7 8/32 bolts with hex head. Use a
lock washer with each bolt. Access to the mounting
bolts is difficult. Use a long hex-wrench for this.
IMPORTANT: Use heat sink compound to cover the
rear of the MB401 mounting bracket completely
before installing. Locate the board as far to the right
(away from the xformer) as possible. Use the two 1"
hex standoffs to secure the board to the bottom plate.
Wiring
: Wire up the rear panel according to the circuit
diagram.
Wiring note:
Use the #22 wire with the thick insulation
for the AC wiring to and from the power transformer.
Use the #18 wire for the wire to the loudspeaker
terminals and between the PS111 and the MB401
board. Use #22 wire for all other interconnect.
Chassis grounding
. Solder the 2400Ohm, 2W
resistor to a solder lug. Solder a length of black wire
to the other end of the resistor. Install solder lug
under one of the hex standoffs of the MB401 board.
Connect the wire the GROUND connection (terminal
marked G of the three position terminal block) of the
MB401 board. This will connect the chassis of the
amplifier to the DC ground of the power supply.
!!!! Assembly is now complete. !!!!
Initial power up.
The first time power is applied observe any unusual
events, like smoke, etc. Turn the power off
immediately if this happens and check for correct
construction. It is best to power up initially using a
variable power transformer (variac) and observe
operation at about half line voltage.
The bias current of the amplifier board now needs to
be adjusted. Connect a DMM between testpoints TP1
and TP2. With no signal on the input and no
loudspeaker connected use R33 to set the bias of the
MB401 main amplifier board to 50mV.
The heatsinks will become warm during normal
operation. When the amplifier is powered up but no
power is delivered the heatsink should become just
slightly warm to the touch. If they become hot in this
mode check the bias current of the MB401 amplifier
module.
With full AC voltage applied the V+ reading should be
approx. 80V (referred to ground), the V- reading -80V,
the V++ r92V and the V-- -92V.
Figure 6 : Mounting of power transformer
Metal Plate
Nut
Rubber washer
Chassis bottom
Transformer
Bolt
Rubber washers
Use two of these.
