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I think L403 is coming off the board tomorrow....
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73
Karl
KI4ZUQ
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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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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
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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
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Karl, previously you wrote that "The signal is also present on pins 1&2 IC408 but not on pins 3,4, 12 thru 15"
Has this changed?? This is proper switching - the signal being seen on both parts of one coil,? but not the others.
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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
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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.
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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.
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Stan, signal present at BNC, pin 5 IC408 and not present at pin9 IC402.
The signal is also present on pins 1&2 IC408 but not on pins 3,4, 12 thru 15. The signal pins 1&2 IC408 are same phase. The signal thru L403 arrives at pin 11 of IC402 a mess about 4 x the base freq of 14.074 mhz, reduced amplitude.
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Might be bad joints in L403 and probably L401, 404 & 405....
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73
Karl
KI4ZUQ
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I was kinda counting on seeing that 10x signal! I will take you test sequence and report back. Thanks!
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73
Karl
KI4ZUQ
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The signal at IC405/406 should be about 10x larger, so easily visible.
If your scope really lets you see that smaller 17mV signal (my cheap scope gives up well higher that level), you should be able to trace the smaller signal through the receiver section.? Look at IC 408 pin 5, the signal after the t/r switch, and then IC402 pin9, the output of the band selector mux.? Those two points will help see where the signal disappears.
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Finally got a 14.074 mhz signal into the QMX+ at about 17 mv. My Rigol DS1102E scope may be insufficient for this task but I can display the 17 mv signal at the BNC? but nothing at pins 1 and 7 on either IC405 or 406. So my problem? is likely back towards the BNC...
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73
Karl
KI4ZUQ
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Thank you, Stan, for being the lighthouse in the storm!
Sometimes we all need someone else to shine a light into our rabbit-hole and help us back out.?
Stan KC7XE?
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Just to see how far up my head has been during this 'cranial-rectal inversion' I did a continuity test C422 to R413/R416 which was, of course, successfull!
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Thank you, Stan, for being the lighthouse in the storm!
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73
Karl
KI4ZUQ
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I have been probing R213 and R216! Talk about blinders!
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73
Karl
KI4ZUQ
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On Wed, Mar 19, 2025 at 01:43 PM, Karl wrote:
The other end of C422 should do the same for R413 and R416 ends towards the rear of the pcb..but the connection is open
Karl, exactly where are you probing for R413/R416?? You say "towards the rear of the PCB", but R413 and R416 are located on the bottom of the pcb, directly under IC405, as are the resistors for the other section of that op-amp.?? So I'm wondering if you are mistaking R513 or R516 for the correct point - that would of course have an open circuit.
An easier place to probe for continuity of that same trace is at pin 2 of IC405, adjacent to where you probed for the other side of C422.
Stan KC7XE
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Additionally, there is a second REV 1 board with the same problem. I have two case numbers with Hans dealing with this.
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73
Karl
KI4ZUQ
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I have some pin-sharp probe adapters for DMM normal probes that poke through that durable film that seems to cover all the SMD joints. The connection, for example between C422 and pin 1 of IC405 can be verified as good. The other end of C422 should do the same for R413 and R416 ends towards the rear of the pcb..but the connection is open. Numerous probings yield no connection. It is either a pass through or a missing/broken/incomplete trace.
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73
Karl
KI4ZUQ
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Karl, how are you testing for a continuity break between those capacitors and the IC inputs?? It would require a board fabrication error, or faulty soldering on the capacitors or ICs to cause such a fault, so while certainly possible, it seems unlikely.? It seems more likely a measurement error, perhaps a layer of flux on the capacitor terminal or IC pin preventing good contact of the probe?
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And no, such a fault would not render IC407 with no signal to process.? Each of these is a feedback capacitor, which helps stabilize and improve the performance of the amplifier - so yes, it is an important part of the circuit to keep performance high, but it would not inhibit the signal from going through and being amplified.
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Stan KC7XE
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Karl