Minolta Di551 - 120V 15 amp

[iam]

Hi,

I have a Minolta Di551 copier powered by 120V 15amp. When I use a
stepdown transformer 115V, 1.5kva for this copier, it does not work.
However it work when I use a 110V, 1.1kva transformer!

The only setback is after a while, the plastic around one of the leg on the adaptor (2 legged) coupling the copier to the transformer, get burned and power tripped. It happened twice after 5000 prints each.

What can I do to prevent this from happening? Appreciate very much
for any advice.