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Re: TR7 next problem
¿ªÔÆÌåÓýIf that oscillator is showing anything real (~152 MHz) then it is being selected. This selection is enacted by the application of +10 volts on U502. The VCO board has no other information about the band selected by the band switch.The only other information the VCO gets from the outside world comes in via pin 5/9 (500 KHz Reference) and pin 5/11 (this is roughly 500 KHz as well, and is the result of the 40 MHz Reference, the PTO and the VCO signal divided by N (N being the selected number produced by the band selection logic) and this is the signal that closes the PLL loop. However, even with the loop open and unlocked, the frequency at the output of the VCO should never exceed 80 MHz,? Where are you measuring the 152 MHz? If grounding RFC505 on the away end does nothing, try grounding the other end. If still no change, then ground the physical junction at CR511A, B and CR510 A,B. This should pull the frequency down a lot. If not, ground the Drain of Q504 through a capacitor of about 0.01 uF. That should clearly kill any oscillation and remove any output from the VCO. Then humor me on this one - measure the voltage on the inputs of both 5 volt regulators U501 and U502 when a low band (less than 15 MHz) and a high band (greater than 15 MHz) are selected by the band switch. If there is a switching issue, perhaps BOTH VCO¡¯s are on when High Band is selected. I would have a hard time deriving what would happen in this condition but I am quite sure things would not go well. This is when an oscilloscope would be handy. You could look at the waveform at the output of the VCO, at pin 5/24, the output of the VCO to the radio. You should see ?a nice sine wave of roughly constant amplitude when either VCO is selected. Gary W0DVN
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