On Mon, Aug 26, 2024 at 04:18 AM, Jinxie wrote:
Well, I stand corrected! This thread is the gift that just keeps giving for our resident tech addicts. My fears in my last post proved unfounded. With +4.5V applied to Tune, I still have -6.6V on the output of U9, but +6.6V on phase detector output! How curious. Will this ever get solved? Hmmm....
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Either there is an intermittent contact (on A11A4 or your tune input), or some failure in U1 that gives exactly 6.6V but it is not clear why U1 would fail with that voltage?
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I recommend connecting two meters, or two probes of a scope, one to U9 output, the other to U1 output and look at them at the same time while +4.5V is applied to tune input. If you really see two different voltages check control voltage of U1 at pin 8 to be above 2.5V. (sample and hold is in sample mode). If input at pin3 is -6.6V, pin 8 is above 2.5V, and output is still +6.6V, U1 failed. I find it unlikely though.?
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If you find U9 pin 6 to be intermittent, look at collector of Q4B again to see if the intermittent issue is before or after U5.?
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As a sanity check regardless of above findings: Connect A11J1 to the coax cable again removing any other connection to tune input (battery etc). Check if YTO unlock message is still there, ?A11J1 is still +6V, and whether right side of R34 (unlock detect) is high or low.?
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Ozan
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