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QSC Powerlight 3.4 troubleshooting
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<blockquote data-quote="Franz Francis" data-source="post: 10559" data-attributes="member: 551"><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">Any component level troubleshooting Guru here? </span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">I am troubleshooting an old QSC Powerlight 3.4 amplifier with a power supply problem on both channels.</span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">The design of this amplifier is each channel has its own independent power supply.</span></span></span></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">The channel’s power supply output design is for two independent supplies on the secondary side of the switching transformer. </span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">One is the supply for the output rail transistors which are all testing fine, plus and minus 48, 96 & 144 volts. </span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">The other is the low voltage supply feeding a half wave rectifier design powering the op amps and other biasing components of plus and minus 14 volts. This supply is completely dead. The winding is not reading open with an ohm meter and the half wave rectifier supply is not overloaded which would be associated with a short or suspected faulty component drawing too much current. </span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">The basic schematic on QSC’s website is what it is, very basic with limited information about the switching power supply. I am able to get the channel working by using an external D.C supply. </span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">The other channel of this amplifier is completely dead because of a faulty Pulse width modulator chip therefore I cannot compare readings.</span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">My question, will the low voltage supply on the secondary of this switching design disappear if for some reason the switching frequency or pulse width is incorrect. Thanks</span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">Franz</span></span></span></p></blockquote><p></p>
[QUOTE="Franz Francis, post: 10559, member: 551"] [FONT=Calibri][SIZE=3][COLOR=#000000]Any component level troubleshooting Guru here? [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]I am troubleshooting an old QSC Powerlight 3.4 amplifier with a power supply problem on both channels. [/COLOR][/SIZE][/FONT] [SIZE=3][COLOR=#000000][FONT=Calibri]The design of this amplifier is each channel has its own independent power supply. [/FONT][/COLOR][/SIZE] [FONT=Calibri][SIZE=3][COLOR=#000000]The channel’s power supply output design is for two independent supplies on the secondary side of the switching transformer. [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]One is the supply for the output rail transistors which are all testing fine, plus and minus 48, 96 & 144 volts. [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]The other is the low voltage supply feeding a half wave rectifier design powering the op amps and other biasing components of plus and minus 14 volts. This supply is completely dead. The winding is not reading open with an ohm meter and the half wave rectifier supply is not overloaded which would be associated with a short or suspected faulty component drawing too much current. [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]The basic schematic on QSC’s website is what it is, very basic with limited information about the switching power supply. I am able to get the channel working by using an external D.C supply. [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]The other channel of this amplifier is completely dead because of a faulty Pulse width modulator chip therefore I cannot compare readings. [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]My question, will the low voltage supply on the secondary of this switching design disappear if for some reason the switching frequency or pulse width is incorrect. Thanks Franz[/COLOR][/SIZE][/FONT] [/QUOTE]
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