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Thanks Stan. Let me clarify a couple points.
Source on Q111 = 10.6vdc. With a scope I see a PWM'd square wave from +11.9 to +10. Not returning to 0. My suspicion is that this is due to the Q111 drain floating.?Correction of my statement: At the drain of Q109 is the PWM'd square wave that alternates between 11.9 and 10v. On the other side of the filter at the source of Q111 we have clean 10.6 DC. Where-as in the 5v circuit, the output of Q108 is alternating between 11.9 and 0 volts. And is being filtered to clean 5v DC at VCC.
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No.? L102 and C106 filter the voltage, trying to average it, so it won't go down to zero. Correct. And the filter is working as I would expect. Filtering an alternating 11.9 to 10.0 28% PWM'd square wave to 10.6v of clean DC because it is oscillating between 11.9 and 10v not 11.9 and 0. Obviously not the voltage we want.
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The processor measures this voltage, actually half this voltage, at the ADC_3V3 connection.?
Ok, so that explains why the diagnostic screen shows 6.6v where I'm measuring 3.3 at ADC 3V3. ADC 5V measures correctly at 2.5v.
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Since you see 10.6V ave, the processor's measurement of the ADC_3V3 voltage is likely not working.?? If the processor can't see the voltage on ADC_3V3, it will continue to increase the PWM percentage to try and get it there, giving a too-high voltage.? This causes D109 (when present) to conduct and keep the voltage near 3.3V, and possibly burning it out.? So check carefully to make sure R110 and R112 are in place, and measure the voltage at the ADC_3V3 junction, which should show VDD/2.? Also inspect to and make sure the processor pin where ADC_3V3 is received isn't shorted to something (solder flake, etc.).
R110 and R112 are in place and measure 27k each, in circuit.
ADC 3V3 measures 6.6v.
I used my Super loupe to inspect all of the processors legs and they are clean as a whistle.
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If the above failure is happening, and you bring up the diagnostics page in the terminal program, you would likely see the 3V in 'linear' mode, and the 3V 'duty cycle' equal to 'duty max', which means the processor is trying hard to get the 3.3V smps working but not seeing the result.
They say a picture is worth a thousand words, so please see the attached diags screen and my notes on the schematic incl waveforms at G and D of Q108 and Q109.
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Thanks again Stan!
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Randy, N4OPI |
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Re: Newly assembled QMX, SWR=1.5 with dummy load
If you are worried about series inductance of resistors, best to build a 50 ohm dummy load
of all parallel resistors.? ?Not a series combination of two sets of two 50 ohm resistors in parallel.
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Jerry, KE7ER
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On Tue, Apr 22, 2025 at 07:00 AM, Jerry Gaffke wrote:
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?This might need clarification for some:
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>> Lifting one end is a good way to lift the opposite pad.?
> Donald, you are right. It's good to tell this.
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Lifting one end of a resistor or cap or diode can rip the opposite pad off the board.
That will ruin your day.
Usually easy enough to repair by running a wire from one end of the new part to some nearby pin, but not always.
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I find it much better to use two irons, one on each end of the part.
A SOT23-3 part is easy enough to bend pins on without ripping up pads.
Anything bigger, and I use chip quik alloy applied with a soldering iron to each pin, then a hot air gun,
then very gently pick up the part once it is totally free.
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Also, best not to re-use chip resistors and caps after taking them off the board.
The bits of metal at the ends might still be connected physically,
but the heat and mechanical abuse can separate that metal electrically from the internals of the device.
Keep a stock handy of replacement parts, they only cost a penny or two each.
If you do have to reuse such a part, make sure the metal bits are still solidly attached,
and check the part with a meter for correct value.
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Jerry, KE7ER
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On Tue, Apr 22, 2025 at 07:20 AM, @Ludwig_DH8WN wrote:
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On Tue, Apr 22, 2025 at 04:09 AM, Donald S Brant Jr wrote:
Lifting one end is a good way to lift the opposite pad.?Donald, you are right. It#s good to tell this. ?
I'm doing this only for some SMT packages e.g. small diodes (SOD323), small transistors (SOT23) and some tantalum capacitors (yellow). All of these have tiny metal stripes as contacts. There is a distance between the place the stripe comes out of the plastic case and the solder joint. There the metal stripe could be bend with nearly no force. I would never try this for packages like SOD80 or TO252.
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73 Ludwig |
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Re: Newly assembled QMX, SWR=1.5 with dummy load
Adding Chris's BAT41 and 0.1uF cap to read the peak voltage with a DVM is a good idea, will work great for a QMX.
Han's 20W dummy load does the same, but uses a 1n4004 diode, good for 400 Volts, assembly instructions have the schematic.
The BAT41 is a shottky diode so will be more accurate, but 20W would be close to blowing through it's 100 Volt max spec.
The DVM will see the peak RF voltage from ground, so multiply by 0.707 to get Vrms (the rms voltage of your transmitted signal).
The power out in Watts is then equal to Vrms*Vrms/50, and that should be fairly accurate assuming the RF is a sine wave.
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Chris has two 100 ohm resistors in parallel to form the 50 ohm on the source end of the coax that goes to
some measuring device such as a tinySA, which we assume has an internal 50 ohm termination resistor.
So his circuit is the same as what I was suggesting for the 50 dB attenuator
His 2.5k resistor is very close to the ideal value of 2475 ohms that I had calculated.
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At 10 Watts out into 50 ohms, the voltage across the 50 ohms is sqrt(10*50) = 22.4 Vrms.
And the voltage across Chris's two 100 ohm parallel resistors is? ?22.4v/(2500+50) * 50 = 0.44 Vrms.
Power dissipated by that 50 ohms is? 0.44*0.44/50 = 0.004 Watts.
Even ridiculously small 0402 (imperial size) chip resistors are rated for 0.062 Watts.
Two 100 ohm resistors in parallel present half the inductance so will be more accurate at 50 MHz,
but if using a surface mount chip resistor that shouldn't matter much.
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Jerry, KE7ER
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On Tue, Apr 22, 2025 at 04:38 AM, Chris, G5CTH wrote:
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Re: Power out on 60 mtr QCX+
Hi Ronald
Many thanks for your reply. I have tried adjusting all the low pass filter windings and have taken 0ne turn off each toroid. At first I could only get 1 watt out and after adjusting the windings I managed to get a extra half watt out. I will have to take a look at the board to see if there are any bad joints etc. If you have any other suggestions I would be grateful for any advice. I have already build a 40 mtr version and that was ok with about 5 watts out so not to way this board is only giving me this low power.
73 Keith G4TJE |
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Re: QMX: C107 burned
Daniel, Without the SMPS boards, I measure a resistance of only 250 ohms on the mainboard between PWR_HOLD and GND. PWR_HOLD is connected only to pin 53 of the processor. I therefore conclude that the processor is defective. I cannot replace it with the equipment I have available, and other components are probably also defective. ? 73, Joerg DG0JDE |
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Hello, Yesterday I make a QSO with the internal mic.I like very well the internal mic solution. 73 Nicolas F4EGX Le?mar. 22 avr. 2025 ¨¤?09:47, Hans Summers via <hans.summers=[email protected]> a ¨¦crit?:
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Re: CW Practice / Rag Chew
¿ªÔÆÌåÓýPaul, NA5N, has a good summary here.
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Re: Newly assembled QMX, SWR=1.5 with dummy load
My dummy load uses 4 x 51R 2W SMD resistors connected in series parallel, then 2k5 to 2 x 100R to give a dummy load come 40dB attenuator.? It also has a BAT41 Schottky diode and 0.1 uF capacitor to give the peak reading.? AIUI SMD resistors tend to be lower inductance than through hole ones.
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A dummy load is about third on my list of essential test gear, first is a multimeter, then a controllable voltage and current power supply with voltage and current display, then the dummy load. |
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