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Tech Head - The Technology Section
The Work Bench and Soldering Station
Schematic For Echostar AD3000ip Power Supply
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<blockquote data-quote="Llew" data-source="post: 450931" data-attributes="member: 175007"><p>Hi, It's fed from the 21V line out of the PSU. I had to replace the switch some time back, and from the notes I made, the 21V goes to the +12V regulator U901 which feeds the emitter of the switch (Q903).</p><p></p><p>If no switching occurs, there will be a standing ~12V on the collector of Q903, which is enough to power the vertical polarity of the LNB. Switching is derived from the PowerPC controller chip via Q904.</p><p></p><p>Not sure how the horizontal voltage is derived from this circuit when switched, I'll check my STB when I have time; meanwhile if you could supply some voltage readings of the transistors concerned I could compare with mine.</p><p></p><p>Llew</p></blockquote><p></p>
[QUOTE="Llew, post: 450931, member: 175007"] Hi, It's fed from the 21V line out of the PSU. I had to replace the switch some time back, and from the notes I made, the 21V goes to the +12V regulator U901 which feeds the emitter of the switch (Q903). If no switching occurs, there will be a standing ~12V on the collector of Q903, which is enough to power the vertical polarity of the LNB. Switching is derived from the PowerPC controller chip via Q904. Not sure how the horizontal voltage is derived from this circuit when switched, I'll check my STB when I have time; meanwhile if you could supply some voltage readings of the transistors concerned I could compare with mine. Llew [/QUOTE]
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Tech Head - The Technology Section
The Work Bench and Soldering Station
Schematic For Echostar AD3000ip Power Supply
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