Another Failure 20 with measurements and some test mode?


I currently have the same issues - usually it will just not boot and I get squares in the top row of the LCD with the backlight on. But sometimes I get error 20 and no backlight.
I do have the IRF9Z24NPBF and IRL520NPBF but they’re from china and look fake. I’ve ordered some real ones through mouser now but I’m just wondering if this sorted both issues or is it only the error 20, with something else causing the boot issue?


squares in the top row of the LCD means the LCD is not initialized properly by the MCU -> maybe the MCU is not working (try to measure the crystal oscillations) AND/OR there might be some interference issue with the ribbon cable (try to make it as short as possible) AND/OR there might be a problem with the LCD power rails (either ground or +5V… adding more ceramic capacitors certainly wont hurt).


Thanks for the quick response. I hadn’t shortened the ribbon cable yet so I cut it down as short as possible but it made no difference unfortunately
Also, I forgot to mention that when it goes to error 20, the A / B LEDs flash but they don’t when it displays the squares. That leads me to believe the problem is not with the display but I don’t have anything to check the crystal with


IIRC when I got “Failure 20” the LEDs also flashed once (both at the same time).

I am 90% certain there is something wrong with the 4066 (how it is connected) in combination with the program (how buttons are read - I think it can block the MCU).

Try this:

  1. Add pull-up (10k-100k) to each button.
  2. Add some capacitors close to the 4066 (ceramic + electrolytic combo)
  3. Add some additional short grounding wire between ground planes of both PCBs.


Which circuits did you find particularly problematic?


voncosel - I added several wires. The problems with booting and random restarts stopped (almost) after I added wire directly to the LCD GND pin (the other end is soldered somewhere close to the MCU).
Also worth mentioning are the pull-ups.
I needed to do both to solve this.

Because there are GND floods on both sides of the PCB it might create closed loops. This is not good when considerable pulse current is used for the transformers.
The only issue I can think of might be Low-ESR capacitors (some Nippons I had in stock) I used for the 9V rails - standard capacitors might do a better job limiting the current spikes.


The device measures the current pulses upon boot and calibrates for it, doesn’t it?


It calibrates for some average current. But I guess the low ESR cap will make the rising edge faster -> higher amount of harmonics signals -> more interference.

I planned to make my own PCB with majority of components being surface mount -> that way you can get GND at almost whole bottom layer. But to be honest I am disappointed by the preset programs.
IMO the ET-312 is a hype fueled by the production.