Hardware Switch lite - FAN always ON even on idle

[SamPT]

Hi folks.
I've been installing some rp2040 lately and in one of the units the fan just blows at 100%, this happens on cold start and only stops after power off.
I managed to replace the motherboard with a spare from a donor, but the issue is still there. It's safe to say that whatever sorcery is happening it's not related to any board component, the spare board works perfectly on other units.
I wonder what is signaling the fan to blow at full, the only logic is the ffc coming from display, but are we reading any temperature from there? I need to understand how the fan circuit is built, if anyone can shed some light I would be extremely grateful

 

[jkyoho]

It's safe to say that whatever sorcery is happening it's not related to any board component, the spare board works perfectly on other units.

why dont you replace the fan itself then?

 

[SamPT]

Yeah, the fan is not the problem , I also replaced it with the fan from the doner unit and it still blows at 100%
I guess it's something coming from the display ffc... But I don't know what. Are we doing any temp readings from the display board?

 

[randy_w]

Check your temperatures first, you can do it with status monitor overlay with tesla.

If temperature readings are normal then check the pwm signal on pwm pin (pin 1 or pin 4, can't remember) with a scope, see if the signal is missing