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Nice, good sluething so far.? I agree with your assessment.? Hopefully the fault is easy to find now.

For 20m, the band select should be set for filter "3", which is B4 or pin 1 on IC408.? So that means the signal is going out on pin 1, through L403, and back to pin 2, so you see it on both of those pins.? That also means those two connections to L403 are likely good (or shorted).? The signal at the input of IC402 (pin 11) verifies that something happened in that coil which shouldn't have happened.? Maybe shorted or open windings, or its output not soldered well..

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The signal doesn't split into I/Q until after the T401 trifilar transformer, from its outputs into IC403.? The frequency of the signal will change to about 12kHz out of IC403 and into the reset of the path to the PCM1804, since IC403 is the mixer.

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Stan.

and note that the band select should send the RF through only the selected coil, not through the others, so you shouldn't see it on the other output pins of IC408 or the other input pins of IC402.? Those two chips are multiplexers - send the input sig to only the selected output or vice-versa.

Stan, you must be in Houston, because we have a problem! No matter the freq the signal is present on all L40X coils....there is a whole lot of switchin' not goin' on!

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73
Karl
KI4ZUQ

Karl, previously you wrote that "The signal is also present on pins 1&2 IC408 but not on pins 3,4, 12 thru 15"

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Don't know ... will repeat that test to see and get back...

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Did a voltage check today while band switching and approx 2.5 vdc moved from C401 to C404 when bands 160 m through 6 m. VCC and VDD were nominally 5.0 and 3.3 respectively.

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Have awakened to all the handy test points scattered about!

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73
Karl
KI4ZUQ

Repeat and expanded, explained tests:

Point? ? ?Result

BNC? ? ? ? ?good

IC408

? Pin 5? ? ? ?good

? ? ? ? ?1? ? ? ?good

? ? ? ? ? 2? ? ? good

? ? ? ? ? 3? ? ? good

? ? ? ? ? 4? ? ? good

? ? ? ? ? 6? ? ? ? no

? ? ? ? ? 7? ? ? ? no

? ? ? ? ? 8? ? ? very weak

IC402

? Pin? ?9? ? ? very weak

? ? ? ? ? ?10? ? weak

? ? ? ? ? ? 11? ?noise

? ? ? ? ? ? 12? ? ?no

? ? ? ? ? ? 13? ? ?no

IC403

? Pin 7? ? ? ? ? ? ~55 mhz*

? ? ? ? ?9? ? ? ? ? ? ~55 mhz*

* very strong signal - twice rms of input (see picture)

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73
Karl
KI4ZUQ

Karl, these results are a bit confusing to me.

If I understand, you are putting in a 14MHz sine wave signal at about 15mV, and are tuned to 14MHz.

With that setting, you should see the 14MHz signal at the input of IC408, pin 5, and on its output, but only on pins 1 and 2.? The true output is on pin 1, and it gets coupled through the shared BPF L403 to pin 2.

You should not see the signal on IC408 pins 3 and 4 or anywhere else.? If you do, you likely have a short somehow between L401 and L403, or perhaps a failed IC408.

And the signal should also be seen at IC402 pin 11.? If it is on IC402 pin 11, that would be from the above-stated short.? But since you see it very weakly or not at all on pin 11, it means something is wrong with your soldering or winding of L403.

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The signals you are measuring on IC403 pins 7 and 9 shouldn't be there, or perhaps are from poor grounding during measurement.? And I don't think they are at all related to your input signal, if it is indeed a 14MHz sine wave.

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So check L403 carefully, and any possible shorting to L401.

Stan KC7XE

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I think L403 is coming off the board tomorrow....

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73
Karl
KI4ZUQ