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Hi, I think I have the same problem on my 80-20m QMX.
That crackling noise changes on the different bands and frequencies even with dummy load or an open antenna port? I thought I had some problem with static on the bands but it seems not. Can this also be why I get erratic graphs in the hardware tests?

I do not have the equipment or knowledge to change that IC myself. I would have to get some help in that case.

73
Mikael
SM7UDB

Hi all,

Unfortunately, I have a similar problem. I built a high-band version 3 QMX (shipped on 3/2). Audio, RF filter, and image rejection graphs are terrible, and the noise is so loud that it doesn't change regardless of if a dummy load or antenna is connected. LPF graphs and output look fine. I don't have a signal generator handy, but if I hook my antenna to the QMX and transmit my Icom 703 into a dummy load I can receive the tone over the noise, so something is getting through!?Based on posts discussing similar problems I followed the troubleshooting suggestions and?triple-checked L401 and T401 and verified 2.5 volts to T401. I ordered a PCM1804 from Mouser and asked my elmers to help me with the surgery (SMD are new to me). I'll keep you posted!

Sam WN5C

Which PCM1804 did you order from Mouser?? They have five different models.? I have the same problem.

Thanks!

73,

Frank
K8FXG

That's a good question, I was confused as well. I ended up ordering the PCM1804DB. I didn't see any differences on the specs, and they weren't indicated on the data sheet. I think the model numbers indicate packaging? but as I just ordered one it didn't matter. Good luck on your repair!

73
Sam WN5C

I ordered the same one as Sam. After soldering in place, I used solder wick with rosin to get rid of excess solder, then hot air to insure no solder bridges. Take your time and good luck!
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73, Dan? NM3A

I have posted a ticket on QRPLabs website and have given Hans some pics and screen dumps. I am awaiting his next response. But as it is Easter ? I do not expect anything until it is over.?

73 de Mikael / SM7UDB

Kit. But if there is a problem with the ADC due to fabrication or bad parts I think Hans will have to know. Then I haven’t the equipment to do a swap of the chip.?

73/Mikael