If it is a sealed part using odd bolt heads or rivets then there are likely no easily serviceable parts in there.
This link on converter/chargers has a treasure trove of information: http://dave78chieftain.zxq.net/ConverterInfo.html
You might be able to find a photo of your exact converter/charger. There are user manuals and troubleshooting info on that site as well.
First thing I'd try to find would be the 120v AC main coach circuit breaker and the 120v AC converter/charger circuit breaker to make sure neither has tripped.
Second thing would be to check the main fuses on the converter/charger.
I realize you have to find them first.
Typically you'll have a 120v AC panel and a 12v panel with fuses. Often they are combined side by side in one housing. Wish I could be of more help. Definitely check http://dave78chieftain.zxq.net/ConverterInfo.html
as he has info dating back to the 1960's on his site.