§ 421. Security interest in other property. Except as provided in
section four hundred ten of this chapter, no retail instalment contract
or obligation, or any other agreement executed in connection therewith,
may provide for the creation of a security interest in any real or
personal property, other than the goods which are the subject matter of
the retail instalment sale, to secure the payment of the time sale price
under such contract or obligation or any part thereof; provided,
however, that the prohibition of this section shall not be applicable to
the taking of a mortgage upon real property to secure the payment of the
time sale price of a retail instalment obligation, if the transaction
which gave rise to such obligation was the furnishing of goods or
services for repairs, alterations or improvements upon, or in connection
with buildings upon, such real property. Any such prohibited provision
shall be void but shall not otherwise affect the validity of the
contract or obligation.