Is there a wise way to debug a large code?

[CuriousOne]

As mentioned above, that noise comes from PWM, PWM is used to adjust brightness of the nixie tubes
The HPWM output from the chip is used to modulate bases of all MPSA42 transistors, emitters of which, individually, go into ports of MCU, and collectors are tied to nixie tube cathodes.
That PCB is quite large - about 88x44mm, now I've designed even more compact one, just 70x30mm. Good I haven't put it into production yet - will add capacitor place to PCB.

Actually, reading schematics via PCB is not that hard - just you need to learn it, as you do with normal schematics.

[Ioannis]

I would try first the software filtering as I described to you.

Last resort to capacitors. If something changes, then you would remove old caps and put new, larger or smaller???

Ioannis

[CuriousOne]

Yeah maybe
My software skills are quite limited as you can see from my posts
And by the way, there was another issue which I've fixed now, and quite likely it was also causing the problems
Due to coding error, I had that brightness adjusting PWM routine called 500 times per second (it was placed in middle dot blink loop)
and when you use HPWM statement, instead of changing the current PWM register, Picbasic stops the pwm generator and restarts it with new values (you can check this with oscilloscope) which causes additional noise generation. Now I moved it into segment refresh routine, which happens once per minute (and keyboard input is deactivated during it), so most likely, it should work without capacitor now, but too lazy to take it apart and unsolder

[Ioannis]

Glad you found the logic error on your code. You did just fine!

Ioannis