Ksger T12 Soldering iron

[Admiin001]

I had obtained a Ksger T12 Soldering station and it had a fault where by it would power on and immediately get red hot with an error. After some searching I was led to believe that this was likely caused by the mosfet. I have now changed the mosfet and the iron no longer immediately heats up and there is no obvious error code.

However, the iron no longer gets hot and the screen temperature just stables around 80 something degrees. I have noticed in the far corner that it always remains at 100% (I’m assuming this relates to utilization.)

Could anyone advise on potential causes and fixes for this issue?

[RayRay]

You've changed the mosfet with the exact same model, or a different one? Also, is the GX12 jack properly aliigned? There's a notch that should be on the top center, see the attached pic (any other orientation will not work!), also, some pictures of the internals would be useful.

[Admiin001]

Hi, thank you for your response.

The mosfet was changed to a IRF9317PbF from a AO4409.

The GX12 jack appears to be aligned correctly, as the iron plugs into place without any resistance.

I had taken an image earlier of the replaced mosfet. (Although a close-up and not a zoomed out image).

[floobydust]

30V P-ch Laptop MOSFET's are commonly used, such as TPC8107, AO4409 etc. and the IRF9317 looks fine as an alternate.
When the MOSFET is on, the green LED on the control board will also be on, as well as heater power present at the GX12 connector.

There must be a new bad connection or bad part. You should have 25V power on the Q1 source pins 1,2,3 and about 16V on the gate, so if it's on about 25V at the heater output drain pins 5-8 as well.
If not, I would look at the driver Q2 and if R4 1k is open. Q2 marking "ARNV" is N-ch MOSFET AO3422.

V2.1S schematic is very close to your 2.12S https://www.eevblog.com/forum/reviews/t12-stm32-v2-1s-soldering-station-controller-schematic-etc/

[Admiin001]

Hi, thanks for your response.

I don’t have much knowledge when it comes to SMD components. I have attached a image of the board, could you point out the area which you are referencing, in specific R4 1K and Q2?

[floobydust]

The component reference designator markings are on the PC board silkscreen.
Check the new MOSFET is not upside down, there's not much to go wrong between it and the MCU. Just Q2 and R2, and any soldering.

[Admiin001]

Hi thanks for your response.

I have just checked for continuity between the points you have highlighted and I notice that there is no continuity between R4 1K.

In addition, the led does not seem to emit green. It seems to be off, with a very faint red led.

There also, appears to be none or very low signs of voltage on the 24v area highlighted.

Would this suggest the mosfet replaced is bad or that Q2 is faulty?

[Admiin001]

Bump

[Manul]

What is resistance of the heating element? Write voltage at IRF9317 source, drain and gate while unit is working. Write voltages of Q2 too.