Hi, I am new to this forum but I have been collecting and repairing video game systems for a while now. My favorite system is the Colecovision. I have learned a lot about how to fix broken ones. However, I have not been able to fix the black screen issue. I always clean disassemble the power switch and clean it and resolder it. This fixes a lot of issues. The one thing that stumps me is black screen issue where when powered on your Colecovision displays a blank black screen sometimes with a hum. Has anyone come up with the steps to try and fix this? I am not the best at checking voltages, but I do have a voltage tester, but I don't know what pins to check. If anyone can help it would be much appreciated. I have read a lot of forums on this subject, but very few end with the fix. Thanks in advance.