This IC in on the controller board of our Sebo X4 vacuum cleaner, which suddenly stopped working. At first, I thought it was just a case of dirty contacts, because I dismantled it, cleaned everything, reassembled it and it worked again, but only for a day, then it died again.

There's not a lot on the PCB, just this chip, the blue 8 MHz ceramic resonator (its outer pins connected to pins 3 and 4 on the IC), what seems to be an op amp and a triac, a few capacitors, diodes and LEDs and a load of resistors. For so few components, a replacement board is ridiculously expensive at £100+ and as the vacuum is almost 10 years old it's not worth spending that amount to fix it. Therefore I'd like to try to diagnose it, but without knowing what this chip is, I have no idea what readings to expect from it. I've spent ages in Google, on Mouser, Farnell and various other suppliers trying to find a datasheet but with no success.

I'll happily supply any other photos of the board or any other info that people might find useful. Any help or suggestions would be very much appreciated.

Thanks in advance.

Close-up of the chip.

The whole board

Reverse of the board

  • 2
    \$\begingroup\$ It's made by ST microelectronics BTW. \$\endgroup\$
    – Andy aka
    Jul 25, 2020 at 11:03
  • \$\begingroup\$ Datecode suggests 1999; the barcode label says "02" so probably manufactured in 2002, and the through hole tech suggests it can't be any newer than that. So almost certainly an MCU, probably mask programmed with a "part no" referring to the mask ROM version. So, not reprogrammable. New PCB ... possibly from a dead one on eBay. \$\endgroup\$
    – user16324
    Jul 25, 2020 at 12:00
  • 2
    \$\begingroup\$ Baz Temple - Hi, You said: "[...] suddenly stopped working. [...] I dismantled it, cleaned everything, reassembled it and it worked again, but only for a day, then it died again". That sequence of events suggests that you changed things by what you did - otherwise the device wouldn't have "worked again" even for a day. It also suggests that the unidentified device (an MCU, as stated in the current answer) is not totally dead. This isn't a repair site for consumer devices, but if it was me, I would be continuing to troubleshoot rather than trying to identify the MCU. Good luck! \$\endgroup\$
    – SamGibson
    Jul 25, 2020 at 12:13
  • \$\begingroup\$ For all you know it could be a loose connection in the switch or a break in the mains cord. \$\endgroup\$
    – vu2nan
    Jul 27, 2020 at 3:57
  • \$\begingroup\$ vu2nan - I've already eliminated those possibilities, they were the first things I checked, after the fuse. \$\endgroup\$
    – Baz Temple
    Jul 27, 2020 at 5:30

1 Answer 1


The placement right next to a resonator/oscillator, to LEDs and other control elements makes it extremely likely this is a microcontroller.

So, buying a replacement part won't help you. You'd need the firmware that is (was?) on the old one.

  • \$\begingroup\$ A micro-controller seems a likely possibility, and it increases my curiosity. I spent several years as an assembly language programmer and have written EPROM code in the past. I assume that if it's a micro-controller it'll have pins for things like read/write enable and a data bus. If I can find a datasheet I might be able to tackle it. As yet, I haven't even diagnosed the power supply because I'm waiting for some connectors to arrive to enable me to try to power it up when it's disassembled. I'm asking about the chip now in case I find that the power supply is good and I need to look further. \$\endgroup\$
    – Baz Temple
    Jul 25, 2020 at 11:29
  • \$\begingroup\$ hm, most microcontrollers, and certainly this one, are meant to be used as isolated device without any external data buses. You might be luckily and find a debug port or something similar, but I'd doubt they didn't disable it at the point of programming. \$\endgroup\$ Jul 25, 2020 at 11:32
  • \$\begingroup\$ Hi Marcus. You seem to be well-informed about micro-controllers. Can you point me in the direction of a 'typical' micro-controller of this type where I could get a datasheet and familiarise myself with one? If I can't fix this board I might as well, at least, educate myself. \$\endgroup\$
    – Baz Temple
    Jul 25, 2020 at 11:38
  • \$\begingroup\$ That's actually a pretty hard question! Because: that board looks nothing like it was designed ten years ago (which seems to be the age of your vacuum), so it's hard to pinpoint how early it is. ST has been making microcontrollers for quite a while, but the only 20-pin PDIP packaged ST microcontroller I could find are these 4. not many. All of them could be accurately \$\endgroup\$ Jul 25, 2020 at 11:44
  • \$\begingroup\$ described as "ancient". If you want to work with more modern (and hence, useful and easier to use) microcontrollers: ST has the Nucleo series of evaluation boards (~15 GBP) and they come with all you need to hook that thing up to your computer and get started programming it (in assembler, but more commonly these days in C). Right of me is my minimalist ST microcontroller board, which consists of nothing but a 32-pad SMD IC (the microcontroller), and two decoupling capacitors, so not harder to set up than the DIP controllers of lore. \$\endgroup\$ Jul 25, 2020 at 11:46

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