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Last night while playing with my qmx the receiver went deaf. ?This happened after txing on ssb with IQ mode on and panadapter open. ?I was using a mic connected to the radio. ?The S meter with antenna dropped to nearly nothing and I can only hear white noise now.?
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The radio will still put out 5w. I ran my little signal generator into qmx and on receive I hear nothing at -33dbm. ?At 0dbm (I know quite strong) the signal will get through. ?Any thoughts? ?
Thank you
Ryan?
KK6DZB |
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Awesome. ?Thanks Dave. ?Will do this tonight. ?I hope to not be swapping IC¡¯s. ?It does get a signal if you throw a strong enough one into the antenna port.
?I forgot to mention that it did this (went deaf) and I turned of and turned on qmx and it had receive again for another few minutes then quit again. ?
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Hopefully it¡¯s just a cold joint on my part. ?
Ryan
KK6DZB |
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Well I checked and re soldered all of the? joints for the toroids and still no fix.? Tried a factory reset hoping it would be that simple but nothing.? Now it seems to be even more deaf than before as absolutely nothing will register on the S meter unless I feed the 0DBM signal into the antenna port.? I checked for continuity through the toroid board connections and that seemed fine.? With the signal source connected and checking with a scope the signal seems to get lost at one side T401.? But all of the connections test to be solid and I re-flowed all of the joints.? I am also unsure whether I am tracing this out right with the scope.? I am going through the schematics.? TX still works fine.? Hopefully I don't have to replace IC407 which I have read failed on older versions I have V4.? Any help is appreciated I would like to get this working again.??
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Thank you
Ryan?
KK6DZB |
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Does the signal get lost at the input side of T401? (pin 9 of IC402)
Do you have the qmx on with the same frequency tuned as your input signal? (IC402 is the rx band selector).? Do you see your signal on the appropriate Yx input of IC402 for the band you are on?
Very common issues that silence rx on all bands are 1) the T401 connection to IC402 and its pair; and 2) the input connection to the BPF toroid(s), rx_in. |
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Stan,
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Thank you for the response. ?Yes signal is at 7.020mhz using an elecraft signal generator. ?At -33dbm I can see on the Oscope the signal comes into T401 but not out. The connections have continuity on the board and I reflowed the joints. The receiver is deaf with -33dbm coming in and listening on 7.020mhz. ?If I increase the signal to 0dbm the tone will break through and I can hear it no problem on 7.020mhz. ?So I am assuming the ic¡¯s are ok. ?I am at a loss as the radio was working fine then just lost all sensitivity going from tx back to rx. ?Which makes me think that whatever is controlling rx/tx is not returning to rx and a strong enough signal is breaking through. ?But this is where I am stuck.
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Ryan
KK6DZB |
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I went through and checked again tonight.? Reflowed all of the joints in the rx section. Ran the signal generator.? I see the signal on pin 9 of IC402 and pin 9 of IC403 and the reciever is still deaf.? I am at a loss as to what to try next.? ?I am baffled by the fact I still have tx and it failed without warning.? Really don't want to shelve this thing.??
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Ryan
KK6DZB |
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I'm glad you can see the signal on pin 9 of both IC402 and IC403.? You should also see it on pin 7 of IC403 (the third winding of the trifilar toroid),?
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Next, look at the outputs of the op-amps that feed the PCM1804.? This is after the mixer, so the frequency will be very near 12kHz rather than 7MHz, and will be 10x the voltage swing (if all is well).? Here is the description of this test from Jeff as recorded in the wiki:
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look at pins 1 & 7 of ic405 & ic406. Pin 1 of ic405 should be about 12khz and about 10x of the input signal. ?Pin 1 of ic406 should be the same but 90 degrees out of phase from pin 1 of ic405. ?Pins 7 of each should be 180 degrees out of phase from pins 1 on each chip. ?If these signals are not as described, you have a receive problem further upstream
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And if you see the signals as described, either you have a PCM1804 failure, or you have a failure in your audio output path.
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To determine which of these, consider the following observations: do you get receive audio via the USB computer interface path?? e.g. receive ft8 data in wsjt-x, or see signals with IQ mode enabled in an sdr program like NaP3 or HDSDR?? If you get audio via this path, the PCM1804 is fine, and the fault lies in the audio-out circuits.
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Note that complex ICs do have a non-zero failure rate (even the good ones), so while it is much less likely on an R4 board to have a failure in the PCM1804 or one of the audio-out chips, it can happen.
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Good luck in finding the culprit,? and let us know what you find next. |
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Hi Ryan. Did you ever check to see if Q508 was working properly? This is the switch that turns off the receive signal input while transmitting. Ron On Tue, May 13, 2025 at 22:43 Stan Dye via <standye=[email protected]> wrote:
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Ronald Taylor