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Dreambox Satellite Receiver | Tutorials | Software
Dreambox 500
DM500s 22khz tone circuit board fix
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<blockquote data-quote="Llew" data-source="post: 552564" data-attributes="member: 175007"><p>On your original schematic, the way I read it is as follows - Q71 is a switch, and the 22kHz output line to the base of the transistor will be a voltage on/off signal from the microprocessor. With an on voltage, the LED lights up, indicating low band. This voltage will switch on Q71 and remove the 22kHz signal from the LNB 13/18V line (presumably generated by the LC oscillator C726/L712).</p><p></p><p>With no voltage to Q71, the 22kHz signal remains active.</p><p></p><p>A voltage check on the 22kHz output line (really an input) when changing high/low frequency channels will show whether this signal is present.</p><p></p><p>Ignore resistor value readings when they are in parallel with coils, they can be misleading when checking in-circuit.</p><p></p><p>Llew</p></blockquote><p></p>
[QUOTE="Llew, post: 552564, member: 175007"] On your original schematic, the way I read it is as follows - Q71 is a switch, and the 22kHz output line to the base of the transistor will be a voltage on/off signal from the microprocessor. With an on voltage, the LED lights up, indicating low band. This voltage will switch on Q71 and remove the 22kHz signal from the LNB 13/18V line (presumably generated by the LC oscillator C726/L712). With no voltage to Q71, the 22kHz signal remains active. A voltage check on the 22kHz output line (really an input) when changing high/low frequency channels will show whether this signal is present. Ignore resistor value readings when they are in parallel with coils, they can be misleading when checking in-circuit. Llew [/QUOTE]
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Linux Based Receivers
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Dreambox Satellite Receiver | Tutorials | Software
Dreambox 500
DM500s 22khz tone circuit board fix
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