Heh, just finished repairs on a mk2 sc-55 and it works! 😊
The unit was in a very rough shape with rust and dirt, a completely dead screen, humidity stains and a missing upper cover (a friend donated to me and it had spent quite some time in storage).
Cleaned it once and was dead. After closer inspection I found that there was a hairline crack on the bottom side of the pcb that affected 2 lines and 3 planes. Luckily since the sc-55 is an old unit it has 2 layers only (upper and bottom - or I was lucky and the crack was in a place that did not have much parts and/or significant planes in middle layers)

Tested again and it works fine despite the rust in all connectors and control pcbs 😊 supdrisingly the sound is also fine! Enjoy somepics of this ghetto mk2 on the test bench 😵 🤣

Ps. If you happen to spot a dead sc55 for sale please give me a heads up 😊 thanks!