开云体育

I just finished up my QMX assembly. The radio power up properly but It does not receive any signals and does not transmit. I am only getting white noise in my earphones. Any suggestions about where I should start troubleshooting it?

Hi Keith,

Since both transmit and receive have issues, it would point to a common component failure.? These would be the circuits from the BNC to Q508.? I would start with verifying the BNC connector is not shorted or open.? If it checks out, then verify that T507 is OK.? From there, it is a systematic checking upstream to Q508.? Along the way, verify that the LPF diodes are working correctly.

What kind of test equipment do you have?
73
Evan
AC9TU

I dont have test equipmemt, just a digital volt meter.

Basic question but did you load firmware?

-mike/w1mt

Basic questions are good! Yes I did!

Cool. What do the rf plots look like?

-mike/w1mt

I have not got that far yet.

BNC shows a short between the centerpin and outside of component. I suspect the may be a short or problem with T507. Does this seem right?

Yes, that is correct. Confirmed by reviewing T507 in the schematic.
Won't have continuity at rf frequencies.

-mike/w1mt

Keith,

The "test" for the BNC short is a close inspection.? That is best done with a Jewelers' Loupe.? Mike stated that T507 has windings that are short circuits for DC voltages.??

Also, visually inspect the top and bottom of the mainboard around the BNC and LPF areas.? We are looking for a short.

As Mike suggested, doing an RF sweep might give us more information.? You need a 50-ohm dummy load to do the RF sweeps.? If you do not have a dummy load, you can use a 50-ohm resistor for the sweeps.

If you plan on building more kits, you might want to invest in a QRP dummy load.?


Other vendor products include SWR and power measurements that cost more:


73
Evan
AC9TU

Thanks for the help Evan. I did a close inspection with a jewelers loupe and did not see a short. Could a short in T507 windings cause the problem?? ?I have a QRP dummy load and SWR Meter however there is no power output at all. I will try to figure out how to do the RF sweeps. Do I use the terminal program to do the sweeps?? Thanks for your patience!!!

Keith N8CEP

Keith,

Yes,? to both of your questions.?

A short on the windings or an open on one of the primary windings could cause your symptoms.?

You use the terminal program for the diagnostics, including the sweeps.? Please read the operations manual on setting up and using the terminal program.? To avoid an extra turnaround, what OS do you have on your PC?? The OS will change how we describe answers to your questions if you encounter issues getting the terminal program to work.? I am most familiar with Windows, but I could provide some help with Linux.? I do not have access to Apple iOS devices.? You will need support from others in the group to use iOS.

73
Evan
AC9TU

OK Evan, I am using Windows 10 and I found and downloaded PUtty. I am in the terminal program successfully.
I am connected to my QRP dummy load. What am I looking for when I do the sweeps for each band?

Keith N8CEP

The RF sweeps look like the ones in the manual. All other hardware diagnostics were ok. I did have trouble during assembly installing T507. Maybe I should think about taking it out and rewinding it.

Kieth,

You will want to run the audio sweeps, the RF sweeps, and the image sweep.? This will let us know where the problem might be.

The sweep value should be higher than -10 for the highest value and less than -30 for the image.

Run the sweeps and let us know.? It is best to post the pictures or screenshots to this thread so we can view them.? You do not need to run all of the bands at this time.

73
Evan
AC9TU

Keith,

Can you post the audio and RF sweep for the band you will use the most?

73
Evan
AC9TU

Kieth,

Another thought: can you verify continuity from the BNC to one side of C526 and not the other?

73
Evan
AC9TU

Evan - YES,? there is continuity from the BNC center post to one side of C526 but not the other. I am going to do the sweeps now and post them.
Keith N8CEP

Here are my Audio RF and Image sweep screen shots

Hi,

I would check also if the C510, C526 values are OK and the T507 primary (one turn) is not scratched somewhere.

73 Bojan S53DZ