Kevin Ross wrote:

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.

If the unit works on batteries but not on the adapter, then it is
probably safe to assume that the power the unit needs is not being
provided by the adapter. This could be due to a faulty adapter or a
regulator circuit in the unit that is not converting the input from the
adapter properly. There might be a bad rectifier, bad capacitor, open
conductor, or any number of faults even if the adapter is good. Only by
opening up the unit and taking measurements can you arrive at the reason
it will not work with the adapter.