SWR WorkingPro 400 Service Manual page 6

The Overload circuit operates simply by monitoring
several stages of the amplifier. If any of the sense
points rise above
(approximately 12V), the Preamp Clip LED will be
illuminated.
Rear Panel PCB
The rear panel PCB is connected to the main
preamp PCB through two 8 circuit cable assemblies
(P1-2 / P201-202). There are five signal circuits
that are routed to the rear panel: Direct, Line,
Headphone, Effects Send, & Effects Return. The
other signals are for power & control.
The Tuner Out comes from the "Direct" signal, and
is not affected by the tuner mute.
The circuitry around U202 is for the XLR &
Unbalanced Out jacks (J204 & J207).
switches the Line Out source from "Direct" to "Line".
Two muting points (Q201-202) mute both the XLR
out and the Unbalanced Out jacks. The Pad switch
at S203 attenuates the signal by approximately
10dB. U202B inverts the signal for the balanced
output. The Unbalanced Out also taps from the
output of U202B.
The effects send comes directly from the main PCB
U6B, after the tone section. As described earlier,
when a jack is inserted into J203, the ring is
grounded, enabling the Effects Blend control.
The Footswitch was designed so that it could work
in parallel with the front panel buttons. LEDs on
both the footswitch and the front panel will track the
the overload threshold
S201
WorkingPro™ 400 & 700
(This is the model name for warranty claims)
switching status from both the front panel buttons
and the footswitch.
Power Amp
The power amp has two configurations: the
SWR500 module and the SWR1000 module. The
only significant difference between these two
modules is that the SWR500 module has 3 pairs of
output transistors instead of 4. Also, the SWR500
module uses a lower voltage version of the power
transistor. The PCB assembly is the same for both.
The SWR500 module was intended for lower power
applications, and is
WorkingPro 400. The SWR1000 module is used in
the WorkingPro 700.
The power module receives its high voltage power
from a separate power supply PCB.
provided through three fast-on connections for +HV,
-HV, and Ground.
The amplifier output is at two more fast-on
connections, which are connected to a separate
speaker output PCB. The Speaker Output ground
is the primary chassis ground connection for the
Power Amplifier and also provides chassis ground
reference for the power supply.
The power module also includes a low voltage +/-
15V supply. This low voltage supply is made
available to the preamp through the 9 pin preamp
header. The low voltage supply is derived from a
separate transformer winding which is connected to
two fast-ons on the module. This winding has a
center tap that is connected to the main HV center
tap inside the transformer.
therefore used in the
This is
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