KSGER T12 2.1s soldering station - small explosion, help needed to repair

[tx3m]

Hi all,

First time posting here, but have been reading incognito for years.

After considering for a long time to replace my cheap Chinese soldering iron, with not so cheap again Chinese soldering station, I finally decided to do so. Reading a lot of reviews and watching many different videos, some of which are from members on this forum, I decided to go with the KSGER T12. Apart from the case grounding and the heatsink being over the live traces, it seemed like everyone has a good opinion of it, and considering the price it seemed like a good buy.

A few days after ordering it I had received it at home, and I was very excited to turn it on. But for my surprise when I powered it up, there was just a short bang accompanied by some hissing, followed up with smoke and a nice "pleasant" smell.
No harm was done, I opened it up and trying to find where the problem came from, I noticed that the controller wire was connected the wrong way around. Whoever was assembling the cable, swapped the wires on the controller end, so even that the connector orientation was correct, the GND and Vcc wires were swapped.

There were a few things that got damaged at first glance . Here is a short list:

• Resistor R1
• Big capacitor, 400v 82uF seems to have "tanned" a little next to R1
• Small unidentified capacitor, next to the transformer
• IC next to the small capacitor

As you can see, the small capacitor next to the transformer was what caused all the sound and smoke effects, and is damaged beyond recognition. Right next to it, there is an IC, which is also melted and unrecognizable. In fact, one of its pins is completely missing, so might be a challenge to exchange it.

So what my questions are:

• Would there be someone who can help me find other possible problems which might have occurred, and are not immediately visible?
• Can some of you who have the same version of HW tell me what are the damaged components, so I can find replacement parts?
• Do you think there is a good chance that after replacing the damaged components, it would be back to life again?

I forgot to mention that I did check the controller with a 24V bench power supply, and it seems that there are no problems there, and it is functioning normally.

Thanks everyone for the help

[totalnoob]

Wow, I am sorry that happened, I am very happy with my KSGER soldering station, but then I'm not an electronics person, I used having to repair my RAS as my excuse to buy it. First thing I would do is contact the seller.  If you're lucky, they'll send out a new one and not ask for the defective one back which would allow you to play with it and perhaps get it up and running and have the second one as a "spare" or leave untouched while experimenting with the repaired one (i.e. trying the CFW DavidAlfa made, links in the CFW thread). 

Beyond that, I can't help you, I'll leave that to others more electronically inclined than I.

[tunk]

Contact the seller. But if you bought it on eBay, Aliexpress etc., ask for a
refund. If reshipping, they may say they "sent" it, when in reality they didn't
reship it at all.

If you cannot fix it, you could try to run it from an 18-20V laptop charger.

[floobydust]

Yes, get a refund or replacement PSU. I would say the power mosfet shorted, took out the SMPS IC and cap, resistor etc. so lots of bad parts.

I drew a schematic of that power supply here.

[tx3m]

During the course of today, I actually got a refund. And with it I have already ordered a new T12 soldering station, with the newer SW and HW version.

I still have this one here, as the seller didn't want it back. And because of this, I will be really keen on fixing it, or at least try to fix it.

[tx3m]

Yes, get a refund or replacement PSU. I would say the power mosfet shorted, took out the SMPS IC and cap, resistor etc. so lots of bad parts.

I drew a schematic of that power supply here.

Thanks for the schematic! I did go over this thread yesterday, but somehow the link of the schematic escaped me between the attached images.

I will have a closer look over the next days and see if I can find some other bad components.

[tx3m]

Contact the seller. But if you bought it on eBay, Aliexpress etc., ask for a
refund. If reshipping, they may say they "sent" it, when in reality they didn't
reship it at all.

If you cannot fix it, you could try to run it from an 18-20V laptop charger.

This is indeed my back-up plan, in case I can't fix it. I am sure I will be able to find a 24V power supply eventually, but I quite like the size of the original one. That is also why I want to first give a try fixing it.

[tx3m]

I couldn't resist the temptation to try and find this mysterious CR8642S.  I found a suggestion in some Slovakian forum, where someone said that there might have been some kind of mislabeling, as this component is not even on the Chip Rail website. So I looked there, and the closest I could find was this guy:
http://www.chiprail.com/pd.jsp?id=53#pfc=%7B%22groupIds%22%3A%5B1%5D%2C%22mul%22%3Atrue%2C%22nvMid%22%3A359%2C%22lid%22%3A1%2C%22sc%22%3A%7B%22key%22%3A%22name%22%2C%22desc%22%3Afalse%7D%7D&_pp=0_359_1

As I am a noob when it comes to power supplies, can some of the more experienced members say what are the chances that something like this would work?

[floobydust]

Sorry I got the wrong IC number on that, I will fix schematic. Used is the Chip-Rail CR6842S, datasheet says part is compatible with SG6842J, LD7552, OB2269.

[tx3m]

Sorry I got the wrong IC number on that, I will fix schematic. Used is the Chip-Rail CR6842S, datasheet says part is compatible with SG6842J, LD7552, OB2269.

And I see that you already updated it. Awesome work mate! By the way, on mine R16(the LED resistor) is 2002 -> 20k. Can you check if you didn't mislabel this one?

And back to fixing the SMPS, I started checking every component and comparing it to your schematic, and here is what I have found so far:

Resistors - R1, R13, R8?, R6, R10?, R18?
Capacitors - C7, C8, 400V82uF(68uF in your schematic), 50V20uF
Diodes - D5, D6
Q3 MOSFET - FQPF20N60C
U2 PWM Controller - CR6842S

I didn't check all the components, but it seems that I will be better off changing all of them on the primary side
The secondary side seems to be intact.

Would you be able to get the BOM for the schematic, so I don't need to write all the components down by hand?

[DavidAlfa]

That looks weird. Like a defective feedback circuit, and the voltage rose out of control. Who knows, these crappy chinese electronics can have mystic powers.

I don't knwo if it's been said already, but when repairing, never connect tehse directly to mains, if there's still something wrong chances are it will blow all again.
Put a 50-100W bulb in series with the mains. If the lamp brights strong, there's clearly a short.
An unloaded power supply will only draw a few watts.

[mastershake]

if you dont get anywhere and want to just replace the whole psu board they are pretty cheap the ksger is less then 14$ and there are a few other cheap ones that work fine also one is less then 10$ usually. sometimes for the price of a replacement vs parts its not always worth fixing these.

[tx3m]

if you dont get anywhere and want to just replace the whole psu board they are pretty cheap the ksger is less then 14$ and there are a few other cheap ones that work fine also one is less then 10$ usually. sometimes for the price of a replacement vs parts its not always worth fixing these.

I was actually looking at some of them. Have you tried and confirmed some of them working properly? If so, would you mind sharing the links here?

And I just wanted to point out, that with this happening I finally learned how this part of electronics works 

Thanks to all of you guys.

[DavidAlfa]

Nice! But yeah, usually not worth the time.
Ordering the parts+shipping will get close to a new one.

[floobydust]

The fuse(s) are way oversized in these power supplies and really it's the 2512 resistors that act as the fuse. That's why there is so much damage from a shorted power mosfet.
There's two 5A (120VAC mains) fuses where the draw is only ~1A nominal and it has an inrush NTC.

[tx3m]

The fuse(s) are way oversized in these power supplies and really it's the 2512 resistors that act as the fuse. That's why there is so much damage from a shorted power mosfet.
There's two 5A (120VAC mains) fuses where the draw is only ~1A nominal and it has an inrush NTC.

I was wondering what would be the current demand of this board. So in this case I guess changing the fuses with a 1.5A or 2A would be enough.

[tx3m]

I just checked the resistance of two of the tips I have. For the K tip its 9ohm and for the D24 its 10ohm. Assuming the soldering iron works at up to 24V, this would give a theoretical value of the max current of 2.66A and 2.4A respectively. So if I put a smaller fuse than 3A, I might be changing it quite often.

Am I missing something?

[DavidAlfa]

These fuses are mean to protect when a catastrophic failure happens. That board failed before the fuse blew, not by the power, the power limit is done in the regulator circuit.
Even putting a smaller fuse won't protect the circuit under a direct short.
99.99% of time these fuses blow because the MOSFET blew up. Maybe a voltage spike, or a fortuite failure.
Also the regulator fail sometimes setting the MOSFET always on.
So I wouldn't worry too much about the fuse.
I've used that power supply at 200% without problems.

[mastershake]

here is one for 10$ i am using one of these right now it works fine. you may even be able to find this one cheaper. i ordered mine for less then 9$ but that seller is out of stock. https://www.aliexpress.com/item/33037808888.html?spm=a2g0o.cart.0.0.289f3c000mceCz&mp=1 or you can get the normal ksger one for around 14$ here https://www.aliexpress.com/item/32816213209.html?spm=2114.12010612.8148356.22.6dd196f1V6sMMB

[kind3r]

I recommended this soldering station to a friend but when he plugged it in the first time it went boom, same symptoms as described in this thread (some pictures: https://photos.app.goo.gl/pL4adwH2G7F4GabZ7) except the 22uF/50V cap next to U2 did not blow up. He got a refund so all is well, but I was thinking about salvaging the unit.

My questions are:
1. t3xm, did you manage to repair yours ?
2. could this have happened just because of the bad CR6842 chip, while other components remain unaffected ? (Did not get a change to test the MOSFET yet)

I know the board is pretty damaged around the blown chip and one of the pins has fused with the copper pad, but still think it's worth a chance since the replacement parts are less than $1.5 (not including shipping cause I need to order some parts for myself anyway).

Just out of curiosity, this one was ordered from BangGood and manufacture date is Jan 2021. Maybe a bad batch ?

[RayRay]

I recommended this soldering station to a friend but when he plugged it in the first time it went boom, same symptoms as described in this thread (some pictures: https://photos.app.goo.gl/pL4adwH2G7F4GabZ7) except the 22uF/50V cap next to U2 did not blow up. He got a refund so all is well, but I was thinking about salvaging the unit.

My questions are:
1. t3xm, did you manage to repair yours ?
2. could this have happened just because of the bad CR6842 chip, while other components remain unaffected ? (Did not get a change to test the MOSFET yet)

I know the board is pretty damaged around the blown chip and one of the pins has fused with the copper pad, but still think it's worth a chance since the replacement parts are less than $1.5 (not including shipping cause I need to order some parts for myself anyway).

Just out of curiosity, this one was ordered from BangGood and manufacture date is Jan 2021. Maybe a bad batch ?

Just get a brand new PSU board for it instead of doing repairs (they're quite affordable!)

If the the station has an IEC C14 connector, get this one:
https://www.aliexpress.com/item/4001181453176.html
And also, check the fuse in the IEC input (you should be able to pry it open with a small flat screwdriver)

If a micky mouse connector (IEC 320-C5) then get this one:
https://www.banggood.com/Geekcreit-AC100-220V-to-DC-24V-Switching-Power-Supply-Board-AC-DC-Power-Module-p-969204.html

*The second kind would require extra handling in regards to grounding**

[tx3m]

Hey, I am sorry to hear that I am not the only one with this problem.

I still haven't gotten around to fixing mine, as I ordered a new one after getting my refund. It is the 3.1 version and so far I haven't had any problems with it.

If I were to fix the original one, I would most definitely take @RayRay advice, and order a replacement PSU. At least where I live, if I were to order the parts which I have found to be damaged it would cost me a lot more than ordering a new one. Of course not excluding the possibility that there still might be other damaged parts that I have missed, which again could cause it to blow up. The version on Aliexpress from KSGER (https://www.aliexpress.com/item/32816213209.html?spm=2114.12010612.8148356.22.6dd196f1V6sMMB) looks good, and you have the option to chose how to connect the AC to the board. Also since now, they have their birthday sale, a price of $11, and free shipping is hard to beat.

Since I already have a working soldering station, I was actually considering looking into making the damaged one work on a 12V supply, which would allow me to use it in a car. This is however just an idea at the moment, and I haven't put any thought into it, but maybe also something you might consider 

[totalnoob]

I don't know how well it would work for soldering, I only did a proof of concept when I received mine, although mine's the "3.1".  The control board powered up and appeared to be running fine on 12V.  It was only a small wall charger that put out 1amp, so I didn't even have the soldering handle plugged in, it was only to see if the unit could be powered up with 12V and it can be.  I think with the new CFW developed by DavidAlpha, KSGER can use a JBC 210 handle (modifications on the handle wiring, I believe, you'd have to check the CFW thread), which uses 12V over the 24V that the T12 and JBC 245 handles use, so you could use that handle on 12V with the CFW.  Not sure what other handle uses a 12V supply.

[DavidAlfa]

Yes, 12v will be fine, but it's the minimum.
Below that, even 11.9V,  it will trigger the low voltage warning to protect the mosfet, as it can work as a resistor and overheat if the gate voltage is too low.
Anyways, you can run 12V tips (or any other voltage) with 24V, just set the max power it can handle (5w min) and the heater resistance, it will calculate the max output by reading the supply voltage to not exceed that power.
It works with  C210, C245 and T12, but could work with another just knowing the thermal sensor levels.

[kind3r]

Thanks for the advice. I told my friend to order a new PSU.
Repairing the old unit is more of a personal ambition rather than a cost saving 

Interesting idea about the 12V 'mod' to use in the car.

Also, LOL @micky mouse connector, never thought of it that way 

[tszaboo]

I remember when I said that the lack of protection on these is disturbing.

Thanks for the schematic. I cannot believe I even considered buying this. Not even a fuse on the output or on the input. if you micro locks up, the iron becomes hotter than the sun. or if ESD kills Q2 gate. Not to mention all the routing and assembly problems. What a piece of junk.

And I got wall of text messages telling me that I expect too much and its actually fine the way it is. 

[kind3r]

My first attempt after replacing R1, U2, Q3 and the 22uF cap went ... not so well: https://youtu.be/-eFd1yWiqpU 
The result was blown R1 and onboard fuse.

So I started looking around and found that D6 and R6 were also blown, replaced them and we're back in business !

Now just need to find some way to replace the stupid THT fuse.

[DavidAlfa]

Always use a 50-100W bulb in series!! 

Pu the battery far as you can from the heat, the life span on these willshorten a lot.
Glueing it on top of the transformer is not the smartest thing!

[kind3r]

Indeed, moved the battery, prepared the case for grounding and also chopped the corner of the radiator that was resting over the PCB trace. Just waiting for the fuse and 1M resistors 

[Ian.M]

The sequence of events when this topology of SMPS blows is:

• For whatever reason the switching MOSFET gets overstressed and blows. As it does so it shorts drain to source and gate.
• The current sense resistor between the MOSFET source and primary side common (negative side of reservoir capacitor) fails open circuit.
• The controller chip gets massive overvoltage (>300V) on its gate drive and current sense pins via the gate and current sense coupling resistors.
• All sorts of parts round the controller chip and the controller chip itself object violently to the order of magnitude or more overvoltage releasing magic smoke!
• Eventually, some milliseconds later, the fuse or other primary side overcurrent protection blows.

After an event like that, *ALL* components round the SMPS controller IC are suspect, even if they don't appear to be damaged.  Also you still have to find and fix the original fault that caused the MOSFET to be overstressed.   That could be anything from a cracked component in the snubber network to a hard short on the transformer secondary + a bunch of other possibilities.  Some faults cause a rapid or immediate blowup, others will come back and bite you hours or even days later.

If you haven't done much SMPS repair work, https://www.repairfaq.org/sam/smpsfaq.htm may help.

The optocoupler is a possible casualty - if its blown open you can get massive overvoltage on the output, so after you've removed the carnage,  worth back-feeding the secondary side output from a bench PSU (with no primary side mains supply) and cranking it up, with a DMM on diode test across the optocoupler's phototransistor.  It should go from open to a few tens to hundreds of mV as the TL431 turns on at the output voltage setpoint.  If it doesn't do that close to the nominal output voltage, or it draws significant current from the bench PSU, you need to take a close look at the secondary side.

You can get push-on axial wire ended caps for standard 20mm fuses, to allow them to be directly soldered as through-hole components.  Check if the blown fuse has these caps - if you are lucky they can be carefully pried off and fitted to a new fuse, otherwise you'll need to buy a pair from a distributor or even Ebay.