Soldering station Quicko T12-943 no power

[Haggis McHaggis]

(not too sure why you opened another thread for this)

This is not my thread, draza opened this topic and posted about it in my thread. These topics are related to some degree. I've no idea why draza is not attending anymore. Would be intresting to hear what the problem was and what can be done to prevent it.

What i want to do is preparing everything before going to use the station in the best possible way and learn something about grounding/ESD.

[Specmaster]

(not too sure why you opened another thread for this)

This is not my thread, draza opened this topic and posted about it in my thread. These topics are related to some degree. I've no idea why draza is not attending anymore. Would be intresting to hear what the problem was and what can be done to prevent it.

What i want to do is preparing everything before going to use the station in the best possible way and learn something about grounding/ESD.

In that case I apologise, I never spotted that the OP were two different members but still firmly believe that the solution to one is the same for other as it only seems to the 943 variant that has these issues, in view 952 is the way to go.

[Haggis McHaggis]

(not too sure why you opened another thread for this)

This is not my thread, draza opened this topic and posted about it in my thread. These topics are related to some degree. I've no idea why draza is not attending anymore. Would be intresting to hear what the problem was and what can be done to prevent it.

What i want to do is preparing everything before going to use the station in the best possible way and learn something about grounding/ESD.

In that case I apologise, I never spotted that the OP were two different members but still firmly believe that the solution to one is the same for other as it only seems to the 943 variant that has these issues, in view 952 is the way to go.

Don't apologise. I'm thankful you and other participate and offer help for beginners like me.

I'm already in the process of ordering a second station, but not sure i should get the 951 (LED) or 952 (OLED) version. I think the LED version could be enough, but who knows.

Nevertheless i want to use the station i already have and want to understand the best grounding method. I wasn't aware that these laptop psus are bad or cheaply designed. They cost a fortune after all.

[Haggis McHaggis]

We don't know what Quicko T12-943 parts are failing, draza did not mention.
Let's assume it is sensitive to overvoltage transients on DC power. The DC on/off switch would cause a power on spike and is trouble. Consider:

LT AN88 Ceramic Input Capacitors Can Cause Overvoltage Transients for detailed analysis and notice the spikes can approach 41Vpk.

Thanks for the document. I overflew it, but unfortunately it's beyond my skills to design a solution from it. The 1.5KE27A you mentioned is probably more realisitic for me. But even with the diode i struggle to choose the right part. I can't interpret the datasheet properly. I think i need a uni-directional type. Would the 1.5KE22A or 1.5KE24A be the right part for this application? My psu is 20VDC.

[floobydust]

You want a TVS that does nothing at 20V (or 24V) yet clamps below the point of damage to the controller. SMD marking code SYTB I couldn't find, it might be an LM2841 max. 45V input. So a 22A or 27A TVS is OK.
Notice app. note 88 also shows adding a bulk capacitance 47uF 35V works very well.
I would put in both the TVS and capacitor, like this schematic.

The Quicko "STM32 T12" controller, I notice the ads on Ali are no longer showing this controller in the T12-943 stations.
It seems to be replaced by the "T12-952 STC OLED" which is back to using a linear voltage reg.

[Specmaster]

The T12-952 controller is same one I have in my stations and I’m happy with their performance.

[Haggis McHaggis]

You want a TVS that does nothing at 20V (or 24V) yet clamps below the point of damage to the controller. SMD marking code SYTB I couldn't find, it might be an LM2841 max. 45V input. So a 22A or 27A TVS is OK.
Notice app. note 88 also shows adding a bulk capacitance 47uF 35V works very well.
I would put in both the TVS and capacitor, like this schematic.

Thank you very much for the schematic. Much more than i could ask for.

[draza]

Sorry,
I was very busy these days.What I found was that S4 Schottky diode is
shorted, I do not have a suitable replacement. No voltage on CPU.
The SYTB is step-down DC / DC regulator chip (LM2841XBMKX).

Does anyone know what this 541IG ic is?

[Specmaster]

I did a google search and cannot find any data on this IC at all so I did a image search and came up with this test of a USB charger meter that uses the same IC and there author seems to think that this is indeed an op-amp ?

https://lygte-info.dk/review/USBmeter%20RD%20Tech%20USB%20Meter%20AT34%20UK.html

EDIT

I just did a search for 5411G (thinking that the I could be a badly printed 1) and bingo, I have the data sheet for this IC which would appear to a voltage detector with built delay circuit and is set at 4.1V.

[floobydust]

Buck-converter diodes failing short has been talked about in this thread: https://www.eevblog.com/forum/projects/interesting-failure-of-buck-converter/
SMT marking "S4" is a Schottky diode SOD-123 package, like a 1N5819 (B5819) or SD103AW 40V 0.2A

These controller boards have the absolute minimum capacitance to just work, and this PCB does not look so great especially the ground pour and putting a high gain op-amp next to the noisy buck converter. I can't see the temperature reading being stable.
Other controller designs use a buck-converter then a 3.3V LDO for quiet power.

The SOT23-5 IC is the thermocouple amplifier, usually a LM321-clone op-amp like SGM8551.
SMT marking "541I" I could not find SOT23-5 parts, it might be a clone of AD8541 (A4A marking).