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Hmmm... my diodes look like they're correctly oriented. I can't locate any evidence of damage or shorts to any components, particularly around the toroids and inductors. I'm absolutely willing to take another swing at the toroids if they're suspect. But I feel like the diagnostic screen gave me a clear pointer toward a problem:



When transmitting, the voltage is at 10.1v (and output of 0 watts!). The operation manual states (p. 73, v.014):

Additionally, the PA voltage is measured,

after the RF envelope shaping (amplitude modulation). In transmit, this should be a little less than

the supply voltage measurement. In receive, it should be near to zero volts. The PA voltage is

coloured green or red depending on whether it is within a reasonable operating range or not."

But in receive, it's still at 10.1v. I see other images in the forum showing that value at, e.g., 0.6v at receive.

Where is this reading being taken? Perhaps I need to look "near" there in the circuit for a nicked wire or a solder whisker??

Thank you for the pointers, John!

I found the setting, and tried toggling it. There was no change in the diagnostic behavior (still showing 10.v on receive or transmit).

I started examining the schematics: was delighted to find that not only is the transmitter contained on a single page, but that all the parts are numbered 5xx to show they belong to the transmitter! So I went hunting 500-series parts to check for clean solder connections/separations. (Those spacing tolerances are super-tight!)

I found & removed a solder ball. Then I hit the jackpot: a testable short between T501 and R506. I cleaned that up and my transmitter voltage dropped to 5.1v. Brilliant!

Though the voltage stays at 5.1v on transmit. Not so great.

I went through tracing other connections in the transmitter, touching up a few of them. Now my voltage in the transmitter is 5.8v (too high), receive or transmit.

I wonder if running it with that short destroyed something else up the line. I'm guessing the BS170's are in decent shape because I can still run SWR sweeps (and they look better now than before: more consistent). I'll continue tracing through the transmitter to see what else I might turn up. Mainly checking for solid connections (continuity).?

I did notice that R507 only seems to present 50ohms of resistance instead of its designated 5.6k. Though since it is in a circuit, perhaps there are other paths I'm measuring when I put my probes on the resistor. Likewise, C507 only seems to present 500ohms of resistance between its ungrounded side and the ground. Again, there may be other paths I do not discern. I'm looking at Q507.

There are some threads that might pertain to Q507. I need to read them tomorrow and see what I can learn about testing it.

Thanks again for pointing me in the right direction!
?
Todd W2TEF

Todd,

Since C507 sits right on the 12V supply, don't expect to see a high impedance there. R507 is a different matter. A resistance of 500 ohms there indicates that Q507, the AOD403, has been damaged. I think you are getting close to a fix now.

73 JZ KJ4A?

On Mon, Jan 1, 2024, 6:44?PM Todd W2TEF <w2tef@...> wrote:

Thank you for the pointers, John!

I found the setting, and tried toggling it. There was no change in the diagnostic behavior (still showing 10.v on receive or transmit).

I started examining the schematics: was delighted to find that not only is the transmitter contained on a single page, but that all the parts are numbered 5xx to show they belong to the transmitter! So I went hunting 500-series parts to check for clean solder connections/separations. (Those spacing tolerances are super-tight!)

I found & removed a solder ball. Then I hit the jackpot: a testable short between T501 and R506. I cleaned that up and my transmitter voltage dropped to 5.1v. Brilliant!

Though the voltage stays at 5.1v on transmit. Not so great.

I went through tracing other connections in the transmitter, touching up a few of them. Now my voltage in the transmitter is 5.8v (too high), receive or transmit.

I wonder if running it with that short destroyed something else up the line. I'm guessing the BS170's are in decent shape because I can still run SWR sweeps (and they look better now than before: more consistent). I'll continue tracing through the transmitter to see what else I might turn up. Mainly checking for solid connections (continuity).?

I did notice that R507 only seems to present 50ohms of resistance instead of its designated 5.6k. Though since it is in a circuit, perhaps there are other paths I'm measuring when I put my probes on the resistor. Likewise, C507 only seems to present 500ohms of resistance between its ungrounded side and the ground. Again, there may be other paths I do not discern. I'm looking at Q507.

There are some threads that might pertain to Q507. I need to read them tomorrow and see what I can learn about testing it.

Thanks again for pointing me in the right direction!
?
Todd W2TEF

Todd,

In FW rev 1_00_011 a feature was added to enable the TX voltage (in RX)? to be set well above zero. (3a: Mod high in RX).

?Leaving it at zero was creating undesired capacitive loading of the RX path and potential diode-induced IMD as well. Restoring some voltage at the drains of the BS170s solves that problem.

Check to see if you have that option enabled on your QMX.

If not, and if you still have voltage showing in RX, there may be a hardware problem with the modulator circuit.

JZ KJ4A?

On Mon, Jan 1, 2024, 3:11?PM Todd W2TEF <w2tef@...> wrote:

Hmmm... my diodes look like they're correctly oriented. I can't locate any evidence of damage or shorts to any components, particularly around the toroids and inductors. I'm absolutely willing to take another swing at the toroids if they're suspect. But I feel like the diagnostic screen gave me a clear pointer toward a problem:



When transmitting, the voltage is at 10.1v (and output of 0 watts!). The operation manual states (p. 73, v.014):

Additionally, the PA voltage is measured,

after the RF envelope shaping (amplitude modulation). In transmit, this should be a little less than

the supply voltage measurement. In receive, it should be near to zero volts. The PA voltage is

coloured green or red depending on whether it is within a reasonable operating range or not."

But in receive, it's still at 10.1v. I see other images in the forum showing that value at, e.g., 0.6v at receive.

Where is this reading being taken? Perhaps I need to look "near" there in the circuit for a nicked wire or a solder whisker??

Hi JZ

An important note about this... You are right that there's a setting to keep the PA modulator high during RX. However: when the diagnostics screen is open, the PA modulator voltage is always low on RX, regardless of the normal setting. Therefore if one sees a high PA voltage in the diagnostics screen when not keying the transmitter, which will be coloured red, it does always indicate an issue with the PA modulator.?

73 Hans G0UPL

On Tue, Jan 2, 2024, 2:26?AM John Z <jdzbrozek@...> wrote:

Todd,

In FW rev 1_00_011 a feature was added to enable the TX voltage (in RX)? to be set well above zero. (3a: Mod high in RX).

?Leaving it at zero was creating undesired capacitive loading of the RX path and potential diode-induced IMD as well. Restoring some voltage at the drains of the BS170s solves that problem.

Check to see if you have that option enabled on your QMX.

If not, and if you still have voltage showing in RX, there may be a hardware problem with the modulator circuit.

JZ KJ4A?

On Mon, Jan 1, 2024, 3:11?PM Todd W2TEF <w2tef@...> wrote:

Hmmm... my diodes look like they're correctly oriented. I can't locate any evidence of damage or shorts to any components, particularly around the toroids and inductors. I'm absolutely willing to take another swing at the toroids if they're suspect. But I feel like the diagnostic screen gave me a clear pointer toward a problem:



When transmitting, the voltage is at 10.1v (and output of 0 watts!). The operation manual states (p. 73, v.014):

Additionally, the PA voltage is measured,

after the RF envelope shaping (amplitude modulation). In transmit, this should be a little less than

the supply voltage measurement. In receive, it should be near to zero volts. The PA voltage is

coloured green or red depending on whether it is within a reasonable operating range or not."

But in receive, it's still at 10.1v. I see other images in the forum showing that value at, e.g., 0.6v at receive.

Where is this reading being taken? Perhaps I need to look "near" there in the circuit for a nicked wire or a solder whisker??

Hmmm... Good news and bad news.

1. I took voltage readings from Q507 (AOD403) with my 12v QMX powered on as follows:
Source: 11.98v
Gate: 11.88v
Drain: 6.6v

With the device powered off, I measured a 49.8ohm resistance between the source and the gate.?

2. Then I proceeded to remove the Gate (left-most) pin of Q507 from its pad, so that it was isolated in mid-air. Powered on, I measured:
Source: 11.97v
Gate: 11.97v
Drain: 6.6v

Powered off, I still measured 50ohms between Source and Gate and, incidentally, 5.58k across R507 (which had been reading 50ohms).

The voltage into the transmitter was still high at 5.8v in receive and in transmit. I had kind of expected that to fall to 0 with Q507 half-way removed.?

3. Therefore I determined to lift the other leg of Q507. Which I did, resulting in a transmitter voltage of .6-.9v. Beautiful! It seems to me there's a pretty significant chance that Q507 really is the culprit, having been shorted to the transformer (T501) when I initially powered on.

Bad news: In try to lift that second leg of Q507, I plugged in my (smart!) soldering iron but neglected to ensure I had turned it on. I lifted the pad on a perfectly cold connection. If only the operator was as smart as the soldering iron (a nifty Pinecil 2). Argh!





So, my new question: is there any point in ordering a replacement AOD403? Or is my QMX now a receive-only device and expensive code oscillator?

Presently two of the three pads are still good. I wonder if I could make it work by tacking a 5.6k resistor and a 0.1u capacitor on top of the device. I would need to find myself a convenient ground and, more challenging yet, a +12V source.

Hmmm.. that's a brilliant observation. Just wrap a small line around the edge of the board (convenient with the MOSFET in the corner).?



Logically enough, R507 and C507 are next to each other on the PCB. I drew arrows pointing to the sides where they're connected. There is 12v at that point. That's where a jumper to the AOD403 sink should be connected. And there's a small work area there that's relatively clear.??

Thank you for the calm observation and continuing encouragement!

Final update:

I received my parts and removed the AOD403 without further incident. That was so easy I decided to go ahead and plop in the new one. I ended up not being satisfied with how it landed and, in trying to remove it to have another go, I ended up lifting the OTHER leg's pad.?

At this point I decided I may be operating a little too far out of my own current skill-level. So I contacted Jeff Moore and shipped the whole thing off.

Jeff found some suspect solder joints, a distorted (by installation heat) power connector, and added the 1N4148 suggested for my 2023 Rev 2 board. He was able to build back up both solder pads for the AOD403, which is now functioning beautifully. In doing diagnostics he noticed some high and flaky SWR readings and spent a few days head-scratching and replacing a few more parts. A lot of labor on a $100 radio!

But last night I was on the air and, despite challenging band conditions, made a QSO with a friend half-way across the country on my simple wire dipole. We gave each other similar signal reports; him running 75 watts and me, well, on the QMX at 12v.??

Thanks to John for your diagnostic help and encouragement. Thank you Jeff for doing top-notch work and providing an accessible backstop when I finally acknowledged I was out of my tinkering league!?

Two other notes:

Using my device for CW practice, in practice mode, with a QRP-Labs dummy load, it had a terrible thump that made it mostly unusable for that purpose. On the air with a real antenna that thump completely disappeared and it is extremely well-behaved. Ironically, Hans pushed out several firmware improvements while I was without my unit, and v.16 -- with the fixed CW algorithms, was released the day I got it back.

And today comes yet more new firmware with AGC. Wow. I feel like Hans has really cornered the market on a usable, portable, affordable, and uniquely feature-ful QRP transceiver. Brilliant!?