Ksger T12 Sudden Death

[BrokenSolder]

Hello folks, I've had a ksger T12 for a few years not sure if it's original or not as it doesn't look the same as ones I've seen online, it was from banggood a while ago.

I'm just a hobbyist so not an expert, I use the station occasionally and have loved it, it's always worked and never had any problems before, today it's just gone dead.

The power supply appears to be working, led ons and the second board pictured is getting 24v but nothing comes on, display doesn't work and no beeps or sounds, no heat.

I swapped the tip for another one that I've used fine before, it worked I adjusted the temperature and after a few seconds the unit just made a beep and turned off and hasn't turned back on again. No smoke, under a microscope everything seems to look OK, psu seems OK is outputting 24v to the controller board, controller board just has no signs of life. Not sure where to check hope someone could possibly help me, I dont know much about these things from a visual it looks all good to me.

[MathWizard]

It looks like there's solder balls on those connectors, it could use a good cleaning. IDK what version the T12 is but here's a link to a page with schematics and discussion.
https://www.eevblog.com/forum/reviews/t12-stm32-v2-1s-soldering-station-controller-schematic-etc/

What tools do you have? A second soldering iron?

There's a few chip there you can check if they have Vcc, usually the safest way to do that is just probe the near by supply capacitor, because it's pretty easy to short pins by mistake with DMM probes.

What ever it is, it's not a big circuit, so not much should go wrong, and all the parts should be easy to get.

If the STM32 chip had a problem, you would need to get a programmed one, or upload it yourself. IDK the cost of these Ksger units, or controller boards, but it might be cheaper/easier to replace the whole thing, and have a bunch of spare parts.

U5 is probably the Vcc for the display, is it working ? It looks like some 3 terminal regulator, or some mosfet to switch power to the display.

[floobydust]

That is a crappy control board, problem is the 3.3V regulator U5 has no proper heatsink and it roasts and croaks, runs too hot.
Carefully check that you have 24V in and 3.3V out for that IC. It's not an official KSGER controller board I think. Really old ones or bad copies had problems with reliably making a 3.3V rail.

edit:
One mod is here, power the IC input from less than 24V:
https://www.eevblog.com/forum/reviews/ksger-t12-help-me-identify-this-wire/msg5182668/#msg5182668
https://www.eevblog.com/forum/reviews/stm32-oled-digital-soldering-station-for-t12-handle/msg3048556/#msg3048556

[BrokenSolder]

I'll check U5 in a little while, thank you both of you for your replies

I would replace the board as the power supply works I was thinking of just getting a cheap quicko t12 and putting the board in here, however I wanted to get it done quicker than waiting for deliveries from China. I bought this for about £30 years ago and it's been amazing for something so cheap for years their now about £100.  I do have a spare iron which I just don't like the feel of in my hand, find it too big and bulky.  The screen doesn't work, but the whole unit doesn't appear to work neither as it makes no sounds or any sign of life now when being powered on. I will check 3v in a little while 😀

[BrokenSolder]

Sorry for the late reply I've just checked U5 it has 21v going in and no 3.3v coming out, the chip is a SE8533 1831-HF I'm hoping I can find it somewhere easily like Ebay or an equivalent, would there be an alternative you guys or anyone else can recommend that would be better please?

[floobydust]

It badly needs heatsinking. The new part will roast and fail too, guaranteed.
Most controllers use SOT-223 Vregs, SOT-89 is pretty hard to cool with no copper pour on the tab like on this lemon control board. As long as 25Vin is not too much.

Russians some put in big copper wire loop soldered to the tab to make a heatsink, others lowered the input voltage adding a pre-regulator like 7805T+output capacitor by cutting the trace and adding wire jumper from the control board to the added Vreg tacked on the PSU somewhere.

To use just one IC, tack soldering a 7833T sticking up in the air would work.

[BrokenSolder]

Thank you for your help sorry for sounding dumb googling  7833T comes up with hair brushes for me.

Again sorry if this is dumb but would something like this work it's only 2 amps though https://www.ebay.co.uk/itm/254604745234?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5339017918&toolid=10049&customid=Cj0KCQjw_qexBhCoARIsAFgBlesbY1N3VHM2OeE7zJRa-D_JRo9zy7rrNyCqGYLPRTswH-3ugOlDnAUaAro2EALw_wcB&gad_source=1] [url]https://www.ebay.co.uk/itm/254604745234?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5339017918&toolid=10049&customid=Cj0KCQjw_qexBhCoARIsAFgBlesbY1N3VHM2OeE7zJRa-D_JRo9zy7rrNyCqGYLPRTswH-3ugOlDnAUaAro2EALw_wcB&gad_source=1 [/url]

[floobydust]

That can work, a buck-converter from 24VDC down to 3.3V but what happened is they are electrically noisy and the thermocouple op-amp circuit does not like that, the temp readings are not stable. You'd have to add bigger output capacitance/filter or use it to pre-regulate down to intermediate say 8V and then feed the new (3.3V LDO) on the control board from that. Then it won't overheat.

I was thinking of any 3-terminal linear voltage reg like LM7833 I'd bodge one in.

[BrokenSolder]

Would this do please?

https://www.ebay.co.uk/itm/275990320144?itmmeta=01HWBFVEFH2M4H95GD5MZJEMK4&hash=item40424e1410:g:xaoAAOSw6GFk1BiW&itmprp=enc%3AAQAJAAAA8CtqptPv7G9gNdYH%2FtIitLV8k1DMtKoAi3OrYepjov6EXTW4IVcwillfIRpeg%2BtvARMy5BoST8RQ4Kj1X2qbnXnqpr3InZykAu6xR9H2xNWE2AXWiJ3teoN6RMjnccrI4q35gDvf2Izc02TdR6K7TPR%2F1k%2BCVYONLhGn7eoijcbsdi7N%2B2Be6PnNcNE2wAqPrxGOnacbplVnKYFxrypUfG3FWvTFBYCQZVzBG3B8yXghTXd%2FGdMehd4mb3yBwZ1%2BdpXUxM6rBCaNPK%2Fr098upJCo%2F%2B3DuFuhoxgcpysUOyL6Zey2nQ1qul0PwxYqewwWfw%3D%3D%7Ctkp%3ABk9SR-7n7e_iYw

How would i know which pins to connect where on the board?

[floobydust]

No, that's a LM337 which is intended for negative voltages. You could use a LM317 board, bare bones.