How do you repair a Roland TR 707 that won't power up?

Answer 1

That;s a bit of an open question, with very few clues to go on. When trying to find why something isn't working, start by ruling out everything possilble.

Start with the PSU. The PSU input on the 707 is a slightly odd shape and this causes issues with some 707s, including intermittent power offs and failure to power up. I had the same problem. If you replace the PSU make sure the polarity and Voltage are the same or you could do permanent damage. A good source is Boss guitar pedals, they are usually the same as Boss is also Roland.

If this isn't the problem then ask on a music forum such as gearslutz.com, you're more likely to find a knowledgeable owner that on wiki answers