<PAGE>   1
                                                               EXHIBIT 10.12(a)


                    SECOND AMENDMENT TO ACCOUNTS RECEIVABLE
                                 LOAN AGREEMENT


         This Second Amendment to Accounts Receivable Loan Agreement
("Amendment") is entered into as of March 20, 1996, by and between UNI-STAR
INDUSTRIES, INC., a Delaware corporation ("Borrower") and CITY NATIONAL BANK, a
national banking association ("CNB").


                                    RECITALS


         A.      Borrower and CNB are parties to that certain Accounts
Receivable Loan Agreement, dated as of August 30, 1995, as amended by that
certain First Amendment to Accounts Receivable Loan Agreement dated as of
October 27, 1995, (together, the Loan Agreement).

         B.      Borrower and CNB desire to supplement and amend the Loan
Agreement as hereinafter set forth.

         NOW, THEREFORE, the parties agree as follows:

1.       DEFINITIONS.  Capitalized terms used in this Amendment without
definition shall have the meanings set forth in the Loan Agreement.

2.       AMENDMENTS.  The Loan Agreement is amended as follows:

         2.1     Section 1.13 is amended in its entirety to provide as follows:

                 "1.13            'CURRENT LIABILITIES' shall be determined on
                 a consolidated basis for Borrower and the Subsidiaries in
                 accordance with GAAP and shall include, without limitation:
                 (a) all payments on Subordinated Debt required to be made
                 within one (1) year after the date on which the determination
                 is made, (b) loans under the Revolving Credit Commitment, and
                 (c ) all indebtedness payable to stockholders, Affiliates,
                 Subsidiaries or officers, regardless of maturity, unless such
                 indebtedness shall have been subordinated, on terms
                 satisfactory to CNB, to the Obligations".
<PAGE>   2
         2.2     Section 7.3 is amended in its entirety to provide as follows:

                 "7.3             'LOANS.'  Make loans or advances to any
                 person, except (i ) Subsidiaries up to an aggregate amount not
                 to exceed $1,500,000.00, and to (ii ) credit extended to
                 employees or to customers in the ordinary course of business,
                 or to ATG".

3.       CONDITIONS PRECEDENT.  This Amendment shall become effective upon the
fulfillment of all of the following conditions to CNB's satisfaction:

         3.1     CNB shall have received this Amendment duly executed by
                 Borrower.

4.       EXISTING AGREEMENT.  Except as expressly amended herein, the Loan
Agreement shall remain in full force and effect, and in all other respects is
affirmed.

5.       COUNTERPARTS.  This Amendment may be executed in any number of
counterparts, and all such counterparts taken together shall be deemed to
constitute one and the same instrument.

6.       GOVERNING LAW. This Amendment and the rights and obligations of the
parties hereto shall be construed in accordance with, and governed by the laws
of the State of California.

         IN WITNESS WHEREOF, the parties have executed this Amendment as of the
day and year first above written.


"Borrower"                     Uni-Star Industries, Inc., a
                               Delaware corporation
                               
                               
                               By:  /s/ Lawrence Butler               
                               -----------------------------------------
                                        Lawrence Butler, Vice President
                               

"CNB"                          City National Bank, a national
                               banking association


                               BY:  /s/  Phillip Goessler             
                               ------------------------------------------
                                         Phillip Goessler, Vice President