WhitakerAudio J C Whitaker 20 W Stereo Audio Amplifier, Manual

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expansion PWB. This should allow the auto off circuit to shut down based solely on the
circuit time delay, which is nominally one hour, depending on the setting of R209.
• If the amplifier trips off when RYL203 closes, the bias protection circuit, cabinet switch,
and high-temperature sensor can be eliminated from the circuit for testing. Switch the
amplifier off and remove the white wire connected to the SW203 post on the expansion
board that is adjacent to the Loop1 post. Move the brown wire from the Loop2 post to the
now-vacant SW203 post. This will close the interlock loop to the power management
board, and eliminate the bias protection circuit, SW401, and SW203 from the system.
Once troubleshooting has been completed, return the connectors to their proper positions.
6.2 Operational Tests
The following steps should be performed to confirm proper construction and operation of the
amplifier.
– Connect speakers to the right and left channel outputs. Remove any input source from the
line input jacks on the back panel. Apply power to the amplifier
– Using extreme caution, measure the following voltages (+/–10 percent is typical). These
measurements should be taken after the amplifier has warmed up (about 1 minute or
more):
• B+ post on the left channel PWB = +340 V dc. This is the B+ supply voltage for the power
output stages.
• BIAS post on the left channel PWB = –30 V dc. This is the bias supply voltage for the
power output stages.
• Terminal 35Vdc on the preamplifier power supply PWB = +35 V dc. This is the V+ power
supply for the preamplifier power supply board. Note that this voltage should appear about
20 seconds after power is applied to the amplifier (after the high voltage supply has
stabilized).
• Terminal 35Vdc on the power management expansion PWB = +35 V dc. This is the V+
power management for the expansion board.