WhitakerAudio J C Whitaker 20 W Stereo Audio Amplifier, Руководство пользователя

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20 W Stereo Audio Amplifier
RYL204 closes, then there is a problem with the protection loop. The protection loop
consists of the following elements:
• Auto-off time delay = RYL201
• B+ voltage sense = RYL205
• Interlock loop consisting of the high-temperature thermostat (SW203), the bias sense
circuit, and the cabinet switch on the power management expansion PWB
– Carefully measure the V+ voltage on the board; this can be done at the anode of D203. A
reading of +25 V dc should be observed.
– Carefully measure the ac voltage at the ACneutral post on the PWB. A reading of
approximately 0 V ac (referenced to ground) should be observed.
– With a high-impedance voltmeter, measure the voltage at the junction of positive terminal
of C201. When the amplifier is first tuned on, the value will be in the neighborhood of
+1.5 V dc. Over time it will climb higher until if finally causes unijunction transistor Q201
to fire SCR Q203. This will end the auto-off time period and shut down the amplifier.
– Set the Delay Adj trimmer potentiometer for center of travel. This should result in a time-
out period of about one hour, which is a good starting point. Position the Auto-Off switch
to the On position.
– Switch the amplifier off and remove the power cord from the ac outlet. After confirming
that the B+ supply has discharged to zero, mount the power management PWB on the four
standoffs with the foil side facing the bottom plate and re-test the system. Retain the L-
angle brackets for future use.
6.1.1 Troubleshooting Notes
Troubleshooting the power management PWB can present certain challenges. With this in mind,
the following tips are provided. Be certain to turn off the amplifier and remove the ac power
connector from the rear panel before doing any work underneath the chassis.
The first step is to narrow the focus of the troubleshooting work by observing the state of the
relays, as noted in the previous section. Each relay provides a visual indication of the operating
state when viewed from the component side. Use these indicators to guide your efforts.