<PAGE>
 
                                                                   EXHIBIT 10.69

                                                                             TCC


                   AMENDMENT TO INVESTOR PURCHASE AGREEMENTS

     THIS AMENDMENT TO INVESTOR PURCHASE AGREEMENTS (the "Amendment") is made as
of January __, 1997 by and among Coinmach Laundry Corporation ("CLC"), a
Delaware corporation, formerly known as SAS Acquisitions, Inc., Golder, Thoma,
Cressey, Rauner Fund IV, L.P. ("GTCR"), Coinmach Corporation ("Coinmach"), a
Delaware corporation, formerly known as Solon Automated Services, Inc. and
successor by merger with The Coinmach Corporation, Heller Financial, Inc.
("Heller"), Jackson National Life Insurance Company ("JNL"), individually and as
successor by merger with Jackson National Life Insurance Company of Michigan,
President and Fellows of Harvard College ("Harvard"), James N. Chapman
("Chapman") and Michael E. Marrus ("Marrus").

                                R E C I T A L S

     WHEREAS, CLC, Coinmach, GTCR and each of Heller, JNL (individually and
as successor by merger with Jackson National Life Insurance Company of
Michigan), Harvard, Chapman and Marrus are parties to Investor Purchase
Agreements, each dated as of January 31, 1995, as amended by that certain
Omnibus Agreement, dated as of November 30, 1995 (as amended, collectively, the
"Investor Purchase Agreements");

     WHEREAS, the parties hereto desire to amend each of the Investor Purchase
Agreements on the terms and conditions set forth herein.

     NOW, THEREFORE, in consideration of the mutual covenants contained herein
and other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, the parties to this Amendment agree as follows:

     1.  Amendment.  Effective as of July 18, 1996 and without further action by
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the parties hereto, (a) each of the Investor Purchase Agreements is hereby
amended by deleting Sections 3B and 3C in their entirety, and (b) each of the
Investor Purchase Agreements to which Harvard, Chapman or Marrus is a party is
hereby amended by deleting Section 3D in its entirety.

     2.  Counterparts.  This Amendment may be executed in multiple counterparts,
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each of which shall be an original and all of which taken together shall
constitute one and the same agreement.

     3.  Successors and Assigns.  This Amendment shall bind each of the parties
         ----------------------                                                
hereto and their respective successors and permitted assigns and inure to the
benefit of and be enforceable by each of the parties hereto and their respective
successors and permitted assigns.

     4.  Amendment and Waiver. The provisions of this Amendment may be amended
         --------------------                                                 
or modified only by written agreement of the parties hereto.  No course of
dealing between the parties or third party beneficiaries hereof or any delay in
exercising any rights hereunder shall operate as a waiver of any rights of any
such person.

     5.  Descriptive Headings.  The descriptive headings of this Amendment are
         --------------------                                                 
inserted for convenience only and do not constitute a part of this Agreement.
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     IN WITNESS WHEREOF, the parties hereto have executed this Amendment on the
date first written above.


                                 COINMACH LAUNDRY CORPORATION
                                 (formerly known as SAS Acquisitions, Inc.)


                                 By: /s/ Robert M. Doyle
                                     ------------------------------------
                                     Robert M. Doyle
                                     Senior Vice President



                                 COINMACH CORPORATION
                                 (formerly known as Solon Automated Services,
                                 Inc.)


                                 By: /s/ Robert M. Doyle
                                     ------------------------------------
                                     Robert M. Doyle
                                     Senior Vice President



                                 GOLDER, THOMA, CRESSEY, RAUNER FUND IV, L.P.

                                 By: GTCR, L.P., its General Partner

                                 By: Golder, Thoma, Cressey, Rauner, Inc.,
                                     its General Partner


                                 By: /s/ Bruce V. Rauner
                                     ------------------------------------
                                     Bruce V. Rauner
                                     Principal



                                 HELLER FINANCIAL, INC.



                                 By: /s/ Ellen T. Cook
                                     ------------------------------------
                                     Name:  Ellen T. Cook
                                     Title: Assistant Vice President

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<PAGE>
 
                                 JACKSON NATIONAL LIFE INSURANCE COMPANY
                                 (individually and as successor by merger to
                                 Jackson National Life Insurance Company of
                                 Michigan)

                                 By:  PPM America, Inc., its agent


                                 By: /s/ William T. Considine
                                     --------------------------------------
                                     Name:  William T. Considine
                                     Title: Vice President



                                 PRESIDENT AND FELLOWS OF HARVARD COLLEGE

                                 By: Harvard Management Company, Inc.


                                 By:  Timothy Peterson
                                     --------------------------------------
                                     Name:  Timothy Peterson
                                     Authorized Signatory


                                 By: /s/ Jack R. Meyer
                                     --------------------------------------
                                     Name:  Jack R. Meyer
                                     Authorized Signatory



                                 /s/ James N. Chapman
                                 __________________________________________
                                 James N. Chapman



                                 /s/ Michael E. Marrus
                                 __________________________________________
                                 Michael E. Marrus

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