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Hello friends,

Today I started testing my telescopic balcony antenna a probably did a stupid mistake -- I located around 2 meters from antenna. =(

As a result sensitivity of my QCX mini decreased about 10-15dB comparing with my factory assembled RIG (based on S-meter and audio deference). On my factory rig I have S2 but on QCX mini only small notice about station. Also I don't notice any difference when connect or disconnect antenna to QCX mini, only when very strong station on the frequency. Previously doing the same comparison I did not see any difference in reception by QCX and TX500 (without PreAmp). Past months I successfully performed QSO on IV antenna with USA and Canada, thus QCX showed outstanding performance.

I suspect that RF leaks to QCX via paddle wire or my headphones (also I have power cable 0.2 meter long). But most probably via headphones because I see capacitors on dit-dah input for my paddles. and paddles continue to work. Have to mention that Audio Gain also works.

I definitely search existing posts about this problem, but probably someone already faced this problem and have quick check list or solution.

At the current moment have only simple multi-meter =(

I appreciate any help or ideas.

Thank you in advance, 73 de SP2RM

Similar problems showed first suspected: IC4 FST3253.

Yesterday I was able to perform some steps based on troubleshooting page.

I go to BPF Peak configuration and noticed about 0 (zero) level indication and missing sound. I slightly touch variable capacitor (almost no changes) and peak appeared. But behavior of PBF Peak is very strange: from 7 level to 0 almost without changes of capacitor. Second BPF Peak shows about 6 and does not dramatically decreased like first one. Also I measured R1 and R2 and both have about 5.5k which two times less than 10k. And the last strange notice. With changed BPF, I go to main screen with VFO and turn volume gain to max and observed strong modulation like in BPF configuration. On the other side I now can see difference with connected/disconnected antenna.

Probably, someone more experienced might see the reason of this.
Unfortunately I don't have oscilloscope for now, and have to measure by QCX DVM =)

Thanks for

Small update here.

I performed basic voltage measurements on IC chips.

The most noticeable that instead of ~2.5V i usually got ~1.3-1.4V.

Than moved to begging and check T1 voltages and R1,R2 Voltage drops. Interesting, that for R1 and R2 I got 3.6V and 1.4V respectively.

I have no idea what might be a reason for changing resistance of resistor(s) even due to electromagnetic interference. I am planning to take 2 10kOmh from RotA,RotB for experiments.

But anyway, this looks very strange.

Forgot to add, as a result of incorrect voltage divider pins 7 and 8 of IC4 got 1.4V instead of 2.4V. And probably this is the root cause of existing problems (at least hope).

Thank you, Ron.

It was a very small hope because I understood that broken resistors due to electromagnetic interference is something very unusual.

But anyway, this is a good reason to order a few FST and 50PA from qrp-labs (always put off buying PA). Here in Poland it is hard to find genuine TI FST.

Again, thank you a lot.

Just for information. As Ron suggested I pull out two wires from T1 that go to IC4 pins 7 and 9. As a result Voltage of R1 and R2 became as expected 2.5V. Already de-soldered IC4 and wasting for replacement part.

Today replaced IC4 with new FST3253 PH2AB from local seller. Have to say that it is not my first time when I solder chips. I don't think that I overheat it or left joint - performed deep inspection.

Unfortunately I got the same incorrect voltages on 7 and 9 legs of IC4.

? Think that might besbroken Noname FST from beginning.

But anyway, I am very appreciate for any ideas what else I can check till awaiting TI FST from QRP labs.

Many thanks and have a good day! br, Yuri

Thank you Ron again!

I checked output pins before soldering and no shorts or low resistance to ground. After that I soldered FST3253 from QRP-Labs and everything works like before. Only performed alignment again to be on the safe side. Voltage on IC legs (from troubleshooting page) as expected about 2.4V.

br, Yuri