Hello! I know this thread is old, but I just wanted to thank everyone here --- your posts really helped me out! (For context, I'm also a researcher in electronics and informatics.)
My 10-year-old MG6730 suddenly went completely dead (no power and no indicator) after several attempts to recover from a B200 head error.
I tried reconnecting the PSU, but had no luck.
However, based on what I learned from this thread, I disconnected and reconnected the three flat cables from the motherboard to the carriage --- and it worked! The printer came back to life!
I estimate it may have encountered an overcurrent when I tried to get the broken head recognized, and disconnecting the carriage may have reset the internal protector state.
FYI, the PSU alone shows about 8.5V and 10V on its output lines, despite its rated specs of 24V and 36V. I’ve read that this generation of PSUs has an energy-saving mode in standby, where full voltage isn't applied until the motherboard signals for it. That might explain the seemingly low output when testing the PSU in isolation.
Also, for clearing the B200 error after replacing the head, I found a Japanese tech blog that described the following steps, which were helpful (I just googled "canon b200 reset"):
1. Mount the print head and ink cartridges and turn on the printer.
2. When the B200 error appears, turn off the printer.
3. Turn on the printer with the front cover open.
4. After ~1 minute of startup sequence, it will show a "cover open" error.
5. Close the front cover. The B200 error will reappear.
6.Turn off the printer.
7. Turn it on again with the front cover open.
8. After ~1 minute, just before the "cover open" error appears, close the front cover.
9. If successful, it won't show "cover open" or "processing" messages; it will just continue displaying the logo. After about 3 minutes, it should return to the normal main menu.