I have recently purchase a 1982 Sunline and replaced the original converter. If it's a fuse they're easy to replace.
I opened the front door by removing a screw at the top of the converter and found four fuses behind the door, one for each DC line running to various parts of the trailer. If you have one of these old converters, mine was under the couch, you may need to simply replace the fuse.
Though my converter was working fine, it had a decided hum, and placed a lot of noise on the AC line so I replaced it.
1982 Sunline 15.5 SB