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Help- hacking is my only option; need to talk to a washing machine via serial TTL to reverse self-destruct booby-trap (lemmy.dbzer0.com)

submitted 6 days ago by diyrebel@lemmy.dbzer0.com to c/unixities@lemy.lol

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My broken 15 y/o w/m has a serial port tracing to an atmega32L chip. I have a USB to TTL adapter which is set for 5v (as opposed to 3.3v) using a jumper. The TX, RX pins are connected to the RX, TX pins of the w/m, respectively. The power supply pins (0v & 5v) are left disconnected.

I ran minicom -D /dev/ttyUSB0 -b 9600 on the PC with the w/m powered off. Minicom seems to default to an “8,N,1” configuration. When I power on the w/m, minicom flashes a popup saying something like “no connection to /dev/ttyUSB0”. This is a bit bizarre because if powering the w/m triggers that popup, obviously there is a connection of some kind.

I do not have the service manual for the Beko WMD 26125 T and the mfr “lost” their copy. I have only scraps of service docs for a similar model that were leaked to a shitty manual jailing service. The circuit diagram of these docs label the serial port as “EEPROM” (as pictured). I suspect the ISP port is strictly for flashing (programming) the machine while the serial port is apparently for accessing the storage (to see the error state that is stored and perhaps clear it if I am lucky).

The goal is to confirm that the error code is “5” (my guesswork based on LEDs lit in binary [101]). The ultimate goal is to clear this fucking error off so I can use the machine. All components work when hotwired (motor, pump, inlet valves). I believe the error state is the machine caught in a lie. Normally the error states are cleared by pressing a secret button sequence, which the mfr witholds from the owners so they can charge us hundreds to do simple repairs.

What can I do without help from the manufacturer? Am I left with trying different baud rates and configs? What should I try? The w/m software is obviously a closed source, thus the serial config is kept secret from w/m “owners”.

Anti-repair rumor: manufacturers disable serial ports before shipping to block repair. But that practice may have started after my w/m was made ~15 yrs ago.

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[–] towerful@programming.dev 5 points 6 days ago* (last edited 6 days ago) (1 children)

Surely you need to couple the grounds?
Otherwise the USB serial doesn't have a reference for 0v. Might be when the washing machine starts, the 0v is so far different that it resets the USB UART, hence the "no connection" popup

[–] diyrebel@lemmy.dbzer0.com 1 points 6 days ago (1 children)

Perhaps I will do that.

But I guess it’s worth mentioning that I have some bad house wiring. I switched off a light to work on it and got shocked (yeah, in principle for safety I should also turn off the breaker but still this should not happen). When lights are off at night, some LED lights are still very faintly lit. When I was messing with serial port wiring I think I touched the 5v and 0v.. perhaps each with a different hand, and felt a shock. 5v should not shock me but I think my ground connections are maybe dodgy. There is proper ground pipes in the basement but maybe someone wired neutral to ground or something somewhere in the house.

[–] LastYearsIrritant@sopuli.xyz 4 points 6 days ago

The light switch may be switching the neutral instead of hot, I've seen that many times before.

Honestly, forget the washing machine for now, start figuring out what is up with the home wiring, sounds like that's your main problem.

[–] Thorry84 2 points 6 days ago (1 children)

Do you have a scope available to check out the signal on these pins? If you don't I would recommend getting one to debug shit. Something simple and cheap like one of those handheld Chinese multimeter/scope combos are perfect for something like this.

You can also try to directly read the eeprom and see if you can make anything of that, if it's an I2C eeprom you can easily tap into that with something like an Arduino if you don't have the right equipment to directly read it. However in my experience it's hard to make any sense of the data in the eeprom without the source code. And Beko probably had the code burned into the microcontroller directly, with no way to get it out.

I agree it's total BS manufacturers don't release their source code and schematics for stuff like this. Like nobody can do anything with that except repair shit.

[–] diyrebel@lemmy.dbzer0.com 1 points 6 days ago (1 children)

I would like to have a scope or logic analyser. Someone told me a logic analyser would be sufficient for this.. and also sufficiently cheap.

I have an Arduino clone but the EEPROM is apparently embedded in the MCU.

[–] Thorry84 2 points 6 days ago

I use this for quick and dirty stuff: https://www.ebay.com/itm/134994778745

It's hard to get my big proper scope on some stuff, like when repairing something big like a washing machine. So this tiny scope is excellent and just fine for reading slow TTL signals like that. I got mine for around 50 euro, but prices vary depending on where you live and if you get a deal, plus shipping times vary a lot as well.

I would recommend this over a logic analyser because usually with a logic analyser you need to know what kind of signal it is, which you might not know. With a scope you can simply read the signal, figure out what the signal is and then go and decode it if you think it's useful. For example if its just TTL serial data, but with a level shift, you can fix that and connect it to a laptop or something.

But there is a big chance there is absolutely nothing on the serial port. It might just be to run some automated tests in the factory, or a leftover bit on the PCB for debugging boards during development. Sometimes it's more expensive to have a board partner redo their lines than just pay the fraction of a cent to include a connector. If there is something on there, the scope will show what it is.