QCX+ MIni IC Bad Behavior

#116095

I've completed assembly of my QCX+ MIni kit for 20 meters (Rev 3), and I have a control chip that seems to work just fine for 10-60 seconds after power-up, but then after that time interval, the button and rotary encoder inputs are ignored. When the failure happens, cycling the power off and on again doesn't seem to help... but if I leave it turned off for many hours or overnight, the circuit will have a longer period of correct behavior prior to failure.

I've confirmed with a short-wave radio that the 20 MHz crystal is indeed putting out a signal at just about the correct frequency (my short-wave reads the signal frequency as 20.004 MHz), and while powered up, the circuit seems to be otherwise working well--audio is sent to headphones, straight-key depress generates a nice tone, etc. I've even been able to complete a couple of steps of the alignment procedure during those 10-60 second startup intervals when the control chip is functioning nominally.

I've been over all soldering joints several times under my magnifier and can't find any obvious goofs. I elected to include the Shottkey diode in my construction and I noticed in the troubleshooting materials a suggestion to desolder inductor L5 and soldering it directly between pins 20 and 7, but before attempting that, I wanted to post this here and ask if anyone has any other ideas. I also had the thought that maybe I simply have a bad ATMega 328 chip and I might try replacing it with another.

Thanks everyone! :-)
--Brian
AK6EP

#116120

Hi Brian. First question: Is this a QCX+ or a QCX Mini? Confused by the title.?

Anyway, generally speaking, I always look for construction issues. We all have them. Check for bad solder joints especially around the connectors between the control board and main board. Of these, pay closest attention to any ground connections on these connectors. Those require more heat and often are intermittent. A working connection that is not well soldered can open up as things warm up.?

Next, I would check the voltage on pin 26 of the microcontroller. With no buttons pressed you should see zero volts here. With the encoder button pushed you should see 5v there. With the right button pushed you should see ?something less than 5v, like 4-4.5v. With the left button pushed it should show even less.. maybe 3-4v or so. If you don't see those then you have an issue with a connection between that pin of IC2 and the control panel. Also look at resistors R44 and R45 on the control panel. They should measure 3.3K and 1K respectively.

If you aren't seeing three different voltages at pin 26 of IC2, then follow the schematic and the board layout drawings and use your DVM to find continuity or lack thereof and you should be able to narrow it down.?

If you are seeing three different voltages there, then your suspicion of IC2 may be correct.?

The modification you mentioned about moving the inductor only applied to the old Classic QCX board. That isn't needed in QCX+ or QCX?Mini.?

I don't see in the above whether you attempted to do a factory reset or not. If you can do so fast enough while it is working correctly you should try the reset.?

Good luck ... 73 ... Ron

Show quoted text

On Thu, Jan 4, 2024 at 9:23?PM Brian Wise <bcwise11@...> wrote:

I've completed assembly of my QCX+ MIni kit for 20 meters (Rev 3), and I have a control chip that seems to work just fine for 10-60 seconds after power-up, but then after that time interval, the button and rotary encoder inputs are ignored. When the failure happens, cycling the power off and on again doesn't seem to help... but if I leave it turned off for many hours or overnight, the circuit will have a longer period of correct behavior prior to failure.

I've confirmed with a short-wave radio that the 20 MHz crystal is indeed putting out a signal at just about the correct frequency (my short-wave reads the signal frequency as 20.004 MHz), and while powered up, the circuit seems to be otherwise working well--audio is sent to headphones, straight-key depress generates a nice tone, etc. I've even been able to complete a couple of steps of the alignment procedure during those 10-60 second startup intervals when the control chip is functioning nominally.

I've been over all soldering joints several times under my magnifier and can't find any obvious goofs. I elected to include the Shottkey diode in my construction and I noticed in the troubleshooting materials a suggestion to desolder inductor L5 and soldering it directly between pins 20 and 7, but before attempting that, I wanted to post this here and ask if anyone has any other ideas. I also had the thought that maybe I simply have a bad ATMega 328 chip and I might try replacing it with another.

Thanks everyone! :-)
--Brian
AK6EP

#116157

Thank you Ronald, you've given me several things to try!! :-)?
Yes it's a QCX Mini - I apologize for the confusion.?
I did a factory reset and the problem persisted. I neglected to mention that in my previous post..
Thank you again and I'll update the thread if and when I find & fix the problem!
73s!!

#116698

Update: I performed all the tests that Ronald suggested, and the rig passed all of them! The buttons showed all of the proper voltages at pin 26 when each was pressed. R44 and R45 values were also confirmed.

The problem still persists, although I did find several less-than-perfect solder joints along the way, which I've cleaned up.

I've ordered a replacement IC2, which is scheduled to arrive at my house this week, along with a couple of other QRP Labs kits to justify the shipping expense. Fingers crossed!!

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QCX+ MIni IC Bad Behavior