Suspect L9 but really need to know DC levels on diode cathodes when in receive 20m. They change with band switch but not with TR switch.
If correctly near 0 on D3 and D6 cathodes then L9 47uH may have invisibly failed to short with lost inductance/shorted turns which eats your RF. On other hand if stay at 5.13v then suspect open Q5. I managed to kill both with a single solder bridge so can be both.
If static DC levels are switching sensibly then simple diagnostic is swap L9 in from a working filter channel.
Good luck,
-Nick VK2ZTY
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On 22 Aug 2023, at 03:03, laycockc+GIO@... wrote:
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Hi all, trying to workout why my QDX isn't transmitting on 20m & 30m. Built the QDX a few weeks ago, and have many QSOs on 40m and some on 80m. I can receive on all band but transmit on 20 shows no power out, with the LED doing the slow flash transmit as per 40m and 80m.
I’ve checked the continuity on all of the coils to the next component, so the enamel is cleaned of and the wire soldered to the trace, although I had to add a bodge wire for one of the T1 connections! And I’ve generally inspected and re-flowed anything looking suspect, everything
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Trawled the group and came across the diode test, below are my outputs using an oscilloscope. The outputs marked with “Vpp” show the voltage peak to peak, whereas the “V” are DC.
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Any ideas on what to check next?
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Diode
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80 Vpp
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40 Vpp
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20Vpp
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D1
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5.6 Vpp
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5.13 V
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5.13 V
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D2
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5.13 V
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6 Vpp
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5.13 V
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D3
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5.13 V
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5.13 V
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145mVpp
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D4
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6.18 Vpp
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5.13 V
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5.13 V
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D5
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5.13 V
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6.18 Vpp
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5.13 V
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D6
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5.13 V
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5.13 V
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1.8mVpp
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