WhitakerAudio JC Whitaker 20 W Stereo Integrated Audio Amplifier, Manual

Page: 143 / 196

143
20 W Stereo Integrated Audio Amplifier
should light and the filaments on V51 should be visible. Let the amplifier run for several
minutes while observing for any unusual behavior. Be very careful as high voltages are
present in the circuit.
For reference, the following series of events occurs at power-on, listed below in order:
• Power from the front panel On/Off switch (SW51) energizes relay RYL202 on the power
management PWB. This applies power to transformer T51 and transformer T201.
• The start-up time-delay interval begins, determined by R211 and C207 on the power
management PWB. This interval is approximately 30 s.
• Rectifier V51 warms up and begins applying B+ power, which is sensed by the voltage-
monitoring circuit of Q204 and Q205 on the power management PWB. Within about 15 s,
the B+ voltage has built up to 300 V dc or more, which energizes relay RYL205.
• After the start-up time-delay is reached, the auto-off and temperature sense (SW203)
circuits are enabled by the combination of RYL203 and RYL204.
A failure in any of the previous steps will remove power from the amplifier.
11) Using extreme caution, measure the ac line voltage between ground and the load side of
filter FL51. A reading of 120 V ac should be measured on the terminal closest to the side of
the chassis, to which the black #16 wire is connected. A reading of 0 V ac (or very nearly
zero) should be measured on the other terminal—the one with the white wire. If improper
voltages are observed, proceed no further. Remove power from the amplifier. Double check
the primary wiring and correct the problem.
12) Using extreme caution, check for proper voltages at the tube connection points listed in
Table 6.2. All voltages are measured with respect to ground using a high impedance
voltmeter. Variations within ±10 percent are typical. These measurements can be taken from
the top of the chassis by probing into the socket connection points. Take measurements on
the right channel and then the left channel.