IC402 was destroyed. ?I used to see this frequently in Rev 2 QMXs. ?But this is a first for a rev 4 unit. ?It’s hard to say why this happened. ?Usually it is from back EMF when switching from TX to RX mode. ?But there is a protection diode in place for that after Rev 2. ?I tested that and it seems ok. ?Your power out is high compared to many other QMX rigs. ?Maybe if you backed down the voltage to 11 volts or less, it might help prevent that in the future.

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Here is what I found and did:

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1) Disassembled all boards, cleaned with 99% IPA

2) Inspected under 10X stereo microscope

3) Tested on bench AF, image scan and rf scan functions - all found to be very poor

4) diagnosing on the bench found IC402 bad - replaced that chip

5) retested on the bench AF, image scan and rf scan functions - all found to be 100% now

6) Tested TX functions on all bands at 12V.? At 12V power out is 3.6 - 5 watts depending on band - no attempt was made to optimize beyond that

7) reassembled into case and retested everything one last time - now 100% RX, TX all modes, all bands

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Total time spent - about 2 hours

I managed to build my QMX successfully, and in
two days of playing with it fried the receive
function. W1NC Jeff Moore diagnosed and
returned the radio to full function:

IC402 was destroyed. I used to see this
frequently in Rev 2 QMXs. But this is a first
for a rev 4 unit. It's hard to say why this
happened. Usually it is from back EMF when
switching from TX to RX mode. But there is a
protection diode in place for that after Rev 2.

I have proven that it is possible to fry IC402 with too much RF on the input side. :(

Did you have an antenna connected to your QMX while you were transmitting with another radio ?

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