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

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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,


--- Quote from: u666sa on November 06, 2024, 04:48:08 pm ---According to datasheet, VDD_2
VSS_2
PA13
PA12
PA11
PA10
PA9
PA8,
are burned

--- End quote ---
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.


--- Quote from: u666sa on November 06, 2024, 04:48:08 pm ---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.

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


--- Quote from: u666sa on November 06, 2024, 04:48:08 pm ---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.

--- End quote ---
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 ?  :o

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