BST 933 repair electronic board of a welding station following a short circuit

[lamoule74]

Hello everyone,

I recently encountered an issue with my soldering station. I accidentally created a short circuit by placing the soldering tip on a live wire (220 V). Since then, the station isn’t holding temperature properly, although the LCD and other functions seem to be working fine.

I started inspecting the board to identify potentially damaged components. After a few checks, I found several burnt resistors: R66, R68, and R40 (see pictures 1 and 2). I managed to find the resistor values by looking up photos of the board online: R66 and R68 are both 220 ohms (possibly 1/4 W?), and R40 is 300 ohms (0805).

I’m wondering if there might be other components nearby that should also be checked, like the adjacent capacitor C55?

While inspecting the entire board, I also noticed a slight anomaly on the STM32, pins top/left (see picture 3).

If anyone has experience with this type of repair or can offer advice on how to test these components to confirm their condition, I would greatly appreciate the help.

Thanks in advance for your support and advice!

[u666sa]

According to datasheet, VDD_2
VSS_2
PA13
PA12
PA11
PA10
PA9
PA8,
are burned

https://static.chipdip.ru/lib/375/DOC030375482.pdf

Can you get same MCU, desolder the old one, read a dump off of it, put the dump onto the new one, and solder it back, or perhaps use j-tag?

Better yet, if you can find a dump for this station online, use that dump instead.


I'd also check these mosfets and multiplexer, though I don't know how you would check the multiplexer, yet. Plus right in circuit check all resistances, if anything is too off, desolder and check. Check diodes. Electrolites desolder and check.

[lamoule74]

Hi u666sa and thx for your reply,

According to datasheet, VDD_2
VSS_2
PA13
PA12
PA11
PA10
PA9
PA8,
are burned

I wasn't sure it was burned, sometimes they put some marker line to check something.
But according to other google photos' comparisons of the same board, it is not marked.

Can you get same MCU, desolder the old one, read a dump off of it, put the dump onto the new one, and solder it back, or perhaps use j-tag?

Better yet, if you can find a dump for this station online, use that dump instead.

I don't know how to find that, without firmware I can't change it...

I'd also check these mosfets and multiplexer, though I don't know how you would check the multiplexer, yet. Plus right in circuit check all resistances, if anything is too off, desolder and check. Check diodes. Electrolites desolder and check.

OK for the mosfet, diodes, and resistor, but too much time for me to test the multiplexer,
maybe just change it and see if it's working again ?