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.
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.