I have a device (a Roland TR-505 drum machine) that works only on batteries. When I insert the AC adapter (the original, which obviously worked at one time) the device shuts down. The AC adapter appears to be converting the correct voltage at the plug. I don't know much about testing circuit boards. Any ideas as to why this pattern is occurring? Any leads on what I might do to figure out how to repair device without spending a lot of money. It's an old device but it does it's job well and suits my needs when it is working correctly.