Sigma R700 (858D) hot air repair

[jmbinette]

Hi to all,

I have a Sigma R700 (858D clone) and would like to repair it.

PCB is marked SBK858D 2017.01.03

The heater is always ON no matter it is on the holder or not. I troubleshooted the whole circuit and the reed switch is good.
On microcontroller input P0.1, I get 5V when off the holder and 0V when on the holder.

Am I missing something here ? Any other conditions in the firmware would keep the heater ON all the time ?

Thanks !

[Rasz]

start with the triac if it has one

[jmbinette]

start with the triac if it has one

I originally thought about it but it controls according to temp setpoint. This part seems to work.
Standby function isn't working, but it heats to whatever temperature I set.

[Rasz]

you didnt mention temp control working
I see you already found the diagram as I did using your P0.1 clue
https://blog.enbewe.de/posts/2018-06-21-saike-858d-original-schematic/

sure looks like bad microcontroller, or typical Chinese firmware half assedness

how hot is the heater when you put it on the stand? full blast or some low setting? maybe optocoupler is leaky? you could try desoldering transistor in front of it and checking if its still producing heat