Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
Help with partially fried QMX
|
You are correct (as always), Ludwig.? I didn't think of that.
In this case I don't see any risk in removing the 3V smps, so that you can measure the voltage on PWR_HOLD without the processor intervening.
?
[Since we know that the 5V and 3V smps regulators are working, and that there is no short between +12 or VCC with VDD, then there is no risk in removing the 3.3V protection diode.]
?
Thanks for making me think outside of the box again, Ludwig.
Stan KC7XE |
|
On Mon, Apr 14, 2025 at 10:27 PM, Stan Dye wrote:
PWR_HOLD is harder to measure - you may need an oscilloscope: when the QMX processor boots, within about 1/2 second it will assert the PWR_HOLD voltage high, and you want to see the voltage on it before this.Stan, could it be there is a way without an oscilloscope? When the 3.3V SMPS is removed the controller couldn't boot and you may check PWR_HOLD using a DMM. What do you think? Is there a reason not to "start" with the 3.3V board removed, maybe a risk causedby the missing SMPS? ?
73 Ludwig |
|
Your diagnostics page looks fine for an 11V input.
?
On Sun, Apr 13, 2025 at 06:52 AM, Austin K4HYD wrote:
At 11v I see the device auto power on even without the control board connected. As soon as the barrel connector is plugged in the device boots up.The cause of this is one of the following: a) The PWR_ON signal (JP101/JP102 8-pin connector) is getting pulled low.? It should be at the Vin voltage (via pull-up resistor R104).
b) The PWR_HOLD signal (JP101/JP102 8-pin connector) is getting pulled high.? It should be at 0V (via pull-down resistor R105).
c) [less likely] - multiple component failures on the 5v smps.
You should be able to measure the PWR_ON and PWR_HOLD voltages as you turn the QMX on.? PWR_HOLD is easy to measure with a DMM.? If it is significantly below the Vin voltage, that is your problem and you need to find and fix it.? PWR_HOLD is harder to measure - you may need an oscilloscope: when the QMX processor boots, within about 1/2 second it will assert the PWR_HOLD voltage high, and you want to see the voltage on it before this.
?
Since it is worse when you have the control board attached, it suggests that the added load on these two control lines exacerbates the problem.
?
Good luck in finding it - Stan KC7XE |
|
Reflowing the solder fixed the issue with the rotary knobs. Now onto the next quirk...
Supplying 7v 250mA works great, so does 8v. When supplying 9v and above I am seeing the device turn on when fully assembled. If I turn the device off by holding the left rotary button, I see a lingering current consumption of about 75mA. Unplugging the controls board prevents the device from auto powering on. ?
At 11v I see the device auto power on even without the control board connected. As soon as the barrel connector is plugged in the device boots up. Attached is a screenshot with 11v supplied and the controls board disconnected.
|
|
Alrighty, we're in the home stretch now! After another visual inspection of the 3.3v board I noticed I was missing diode D105 from the factory. After salvaging that diode from my old SMPS board, I plugged in the 7v 250mA power supply and booted without issue! Just have one small remaining issue to solve. Every time I rotate the right rotary knob I am seeing a click of the left knob being simulated. This is leading to a behavior where every time I twist the right knob the mode switches between cw and digi. Going to reflow some joints to see if that resolves the issue in the meantime. |
|
The good news is that your attempts to destroy your QMX have failed, at least partially.? The processor still seems to be working.
?
As for voltages you need a good 3.3V supply voltage before you can rely on what the processor measures.? The 3V3 SMPS voltage of 2.57V isn't expected and it is in linear mode. Neither SMPS is running correctly.? Check VDD and VCC to see what voltages you actually have, use a multimeter, be careful not to short between pins.
?
Other things to check: PWR_HOLD should be high (>2V), I expect it is because the processor has pulled it high.? LIN_REG_EN is probably low.? PWM_3V3 and PWN_5V should have pulses on them, a meter might indicate some sort of average.
?
And what sort of current is this taking?? Something may be taking too much current and that's pulling VDD too low for the regulator to cope. Try running without the display and encoder boards plugged in, that will take them out of the equation.?? And try the stand alone SMPS board tests, just in case there's still a problem with one of the new boards. |
|
Ok, so some progress - After reflowing a handful of cold solder joints, some of which were some of the early connections on the initial capacitors, the auto power on problem is now resolved. I did not find any solder flakes, bridges, or other shorts, simply reflowing the solder on some of my connections remedied this issue. ?I am however still seeing the black squares on the display and also realize that the backlight is not on. I've been reflowing the joints on the display board as well as their corresponding connections on the main board but havent had luck so far. Still stuck on black squares across the screen with no backlight. I've also tried reflashing the firmware by jumping the connection on the main PCB as described in the assembly manual but the issue persists. |
|
Ludwig and Stan, Thank you both for your reply. I went ahead and checked the resistance for all the pins related to the two SMPS boards and there only appears to be one point of note. When testing the main PCB without the SMPS boards pluged in the GND to VCC on the pins for SMPS board 1 start off at a low resistance of about 400 ohms then quickly climb to about 50k ohms. Checking GND to VCC on SMPS board 1 shows about 800k ohms. I was having some trouble fully understanding the test setup for the SMPS boards and did not verify with the instructions you sent. I will however note that the boards are brand new replacements and should in theory be working as expected. |
|
On Fri, Apr 11, 2025 at 06:28 PM, Austin K4HYD wrote:
the device still powers on immediately upon being connected to power,You need to fix this first, before worrying about anything else. And yes, please continue to use the low voltage until you get it booted up successfully.? You only need higher voltage/higher current to transmit; all normal cpu and receive functions will work at 7V and 250mA.
?
Since you see this with the display/control panel removed, it is a fault on in your SMPS or on the main board, not the switches.
The things that can cause this are:
1) The PWR_ON signal is shorted low.? Either on the main board, or on the 5V SMPS connector, or in the interconnect.? Note that PWR_ON and PWM_5V are adjacent pins in the connector, so if PWR_ON is shorted to PWM_5V, this would happen.?
2) The PWR_HOLD signal is held high, shorted to some signal that goes high when power is plugged in.? One place this can happen is in the interconnect, the PWR_HOLD signal is adjacent to the VIN voltage in the connector.
3) VIN shorted to +12V.
4) Less likely, but multiple input component failures on the input part of the 5V SMPS.
?
You can debug a lot of this with a multimeter.
Perhaps the easiest place to start is to remove and test the two SMPS boards independently, as described in the wiki here:
And while removed, measure (on the main board) the resistance between all of the pins of the power connectors.? They should all show at least a few k-ohms to ground, and to each other.? If they don't, there is a fault on the main board that needs fixed.
Reading the wiki entry on QMX QMX_plus Startup will also be helpful in understanding what you see.
?
Good luck, Stan KC7XE |
|
Hello Austin,
?
you may test the two SMPS boards off line (see QMX QMX_Plus Power supply test Process ). Immediately switch on could be caused by a failure between "V_IN" and "+12V" on Plug-in PCB #1 (see schematics page 1).
?
If the two SMPS boards are removed please check resistance to GND for all the lines to the SMPS. A failure here could also switch on the QMX without pressing the encoder
?
Reading QMX QMX_plus Startup you will find a description of the start process, which signal should show which level at which step of switch on. There is also a link to a sketch to identify the signals at the mainboard.
?
Please let us know your results.
?
73 Ludwig |
|
Hi Bruce, I've verified that there is an air gap between the dc jack and encoder. I will put some electrical tape on the back of the DC jack to be safe. I also did some additional testing and observed that the device still powers on immediately with draw when the LCD board and controls board are removed. Checked again for any solder bridges or solder flakes and was unable to see anything overtly wrong. |
|
Hi Stan! I just got finished installing the new buck board. I used 7V and 250mA to power the device this time. With USB-C cable plugged in I plugged in the barrel connector and immediately saw that the QMX showed up on my PC and the power supply indicated about 200mA were being pulled. This is still concerning since the instructions specifically state there should be zero power draw until the left rotary encoder is pushed in. I tried unplugging and replugging a few times, also attempted a firmware flash, but the behavior of immediately powering on still persists. After attempting the firmware flash, the device still powers on immediately upon being connected to power, but I now see black squares across the screen where as before the flash I saw no characters at all. I'm still puzzled as to where things are going wrong. I assume the issue that blew out the components mentioned in my earlier post is still lingering somewhere. The reduced power supplied is probably preventing anything from blowing but I'm at a loss as to what's going wrong. Any guidance would be greatly appreciated! |
|
Stan - that was super helpful.? Thank you for taking the time to type that out for me/other hams that want to learn by doing (or by destroying).?
?
After i read the earlier post about the pin to T507 i assembled enough non-panicky energy to actually go and look at the traces in the assembly manual.? Lo, what did I see?? Indeed a direct connection to T507.? I was operating at 7V for a 9V QMX, but indeed over extended period.
?
The support of you, Steve, and others who have answered my questions over the years since my first QCX build gives us electronically-uneducated persons the readiness to venture forth and enjoy this world of home-finished qrp radios.
?
It is all very appreciated. Thank you!
JD |
|
On Wed, Apr 2, 2025 at 08:29 PM, VA2OJD wrote:
Is there a single spot, somewhere on this forum, where it lists key measurements to check when troubleshooting?Have you looked at this forum's wiki?? There is a topic specifically for the BS170s.? It has some helpful diagnostic guidance.? And you can search messages in this forum for BS170 and find a good number of entries, with different people being guided in their diagnostic efforts. ?
Since your QMX was working for a good amount of time, a good possibility is that you fried your BS170s - most likely just them and not the driver and Q507.? This can occur, especially if you are running FT8 at more than 12.0V (for a 12V build) or 9.0V (for a 9V build).? Or if your QMX puts out more than 5W on a band at the correct voltage.? And especially if you combine over-voltage with some higher SWR on your antenna (probably more than 2:1), which can happen intermittently on wire antennas if the wind is blowing.? Doing any of the above over an extended time has risk of gradually beating your BS170s into failure.? That's why Hans has in big red print in his manuals to a) not run above 12V and b) not run above 5W.? And this is especially true with constant carrier modes like FT8, which add heat in the finals to the mix.? CW is more forgiving, because it is lower duty cycle.? At 5W the BS170s are pretty much up to their rated max, so going above any of the parameters puts more stress on them.? [This is true of their use in (tr)uSDX and other QRP radios, too.]
Stan KC7XE |
|
Hi Steve.? Thanks.
So even the CENTER of the BNC?? the middle, radiating contact of the BNC is connected to ground via T507?? MyBS170s look fine.? Is there a way to test them?? It makes sense that they would pop first, but i've no idea how to test them.??
?
Is there a single spot, somewhere on this forum, where it lists key measurements to check when troubleshooting?? I must have made Google a million dollars in eyeball hits in my searches over the last week.
?TNX again!
JD |
to navigate to use esc to dismiss