Document:

<PAGE>
                                                                 EXHIBIT 10.85.1

                                 FIRST AMENDMENT
                                       TO
                                CREDIT AGREEMENT

                            Dated as of June 25, 1999

     This FIRST AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is among
MICROSEMI CORPORATION, a Delaware corporation (the "Borrower"), the several
financial institutions party to the Credit Agreement referred to below
(collectively, the "Lenders"; individually, a "Lender"), CANADIAN IMPERIAL BANK
OF COMMERCE, as administrative agent for the Lenders (the "Administrative
Agent").

                             PRELIMINARY STATEMENTS:

     (1) The Borrower, the Lenders and the Administrative Agent have entered
into that certain Credit Agreement dated as of April 2, 1999 (the "Credit
Agreement"; capitalized terms used and not otherwise defined herein have the
meanings assigned to such terms in the Credit Agreement).

     (2) The Borrower has requested that the Administrative Agent and the
Lenders make certain amendments to the Credit Agreement.

     (3) The Administrative Agent and the Lenders are, on the terms and
conditions stated below, willing to grant the request of the Borrower.

     NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree as follows:

     SECTION 1. Amendments to Credit Agreement. Effective as of the date hereof
and subject to the satisfaction of the conditions precedent set forth in Section
2 hereof, the Credit Agreement is hereby amended as follows:

         (a)   The first paragraph of Section 2.7 of the Credit Agreement is
hereby amended by deleting the figure "$3,000,000" and replacing it with the
figure "$10,000,000".

         (b)   The final sentence of the first paragraph of Section 2.7 of the
Credit Agreement is hereby amended and restated in its entirety to read as
follows:

<PAGE>

         "In no event shall any Letter of Credit have an expiration date later
than the Stated Maturity Date."

                  (c)   There shall be added to the Credit Agreement a new
Section 7.1.11 reading in its entirety as follows:

                  "SECTION 7.1.11. Delivery of Mortgage. The Borrower will
         furnish to the Administrative Agent on or before August 15, 1999 a duly
         executed Mortgage covering its real property interests known as [2830
         South Fairview Street, Santa Ana, CA 92704], together with all
         documentation required by clauses (a), (b) and (c) of Section 5.1.7
         hereof.

         SECTION 2. Conditions to Effectiveness. The amendments in Section 1 of
the Amendment shall be effective as of the date hereof, subject to the
Administrative Agent's receipt of the following on or before June 30, 1999:

         (a)      counterparts of this Amendment executed by the Administrative
                  Agent, the Borrower and Majority Lenders;

         (b)      counterparts of the Consent appended hereto as Exhibit A
                  executed by the Guarantors; and

         (c)      such other documentation as the Administrative Agent or any
                  Lender shall reasonably request.

         SECTION 3. Representations and Warranties.  The Borrower represents and
warrants as follows:

                  (a)   Authority: Enforceability. The Borrower has the
         requisite corporate power and authority to execute, deliver and
         perform this Amendment, and to perform its obligations under the
         Credit Agreement as amended hereby. The execution, delivery and
         performance by the Borrower of this Amendment, and the consummation of
         the transactions contemplated hereby, have been duly approved by the
         Board of Directors of the Borrower and no other corporate proceedings
         on the part of the Borrower are necessary to consummate such
         transactions. This Amendment has been duly executed and delivered by
         the Borrower. Each of this Amendment and the Credit Agreement as
         amended hereby constitutes the legal, valid and binding obligation of
         the Borrower, enforceable against the Borrower in accordance with its
         terms.

                  (b)   Loan Document Representations and Warranties. The
         representations and warranties contained in each Loan Document are true
         and correct on and as of the date hereof, before and after giving
         effect to this Amendment, as though made on and as of such date (unless
         stated to relate solely to an earlier date, in which case such
         representations and warranties shall be true and correct as of such
         earlier date).

                  (c)   Absence of Default.  No event has occurred and is
         continuing, or would result from the effectiveness of this Amendment,
         that constitutes a Default.

                                       2

<PAGE>

         SECTION 4. Reference to and Effect on the Loan Documents. (a) Upon and
after the effectiveness of this Amendment, each reference in the Credit
Agreement to "this Agreement", "hereunder", "hereof" or words of like import
referring to the Credit Agreement, and each reference in the other Loan
Documents to "the Credit Agreement", "thereunder", "thereof" or words of like
import referring to the Credit Agreement, shall mean and be a reference to the
Credit Agreement as modified and amended hereby.

               (b) Except as specifically amended above, the Credit Agreement
and all other Loan Documents are and shall continue to be in full force and
effect and are hereby in all respects ratified and confirmed.

               (c) The execution, delivery and effectiveness of this Amendment
shall not, except as expressly provided herein, operate as a waiver of any
right, power or remedy of any Lender or the Administrative Agent under any of
the Loan Documents, nor constitute a waiver of any provision of any of the Loan
Documents.

         SECTION 5. Execution in Counterparts. This Amendment may be executed in
any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed and delivered shall be deemed to be
an original and all of which taken together shall constitute but one and the
same agreement. Delivery of an executed counterpart of a signature page to this
Amendment by telefacsimile shall be effective as delivery of a manually executed
counterpart of this Amendment.

         SECTION 6. Governing Law. This Amendment shall be governed by, and
construed in accordance with, the laws of the State of New York.

                                       3

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers thereunto duly authorized, as of the date
first above written.

                             CANADIAN IMPERIAL BANK OF
                             COMMERCE, as Administrative Agent

                             By:
                                ---------------------------------------
                                 Name:  Paul J. Chakmak
                                 Title: Managing Director, CIBC World Markets
                                         Corp., AS AGENT

                             CIBC INC., as a Lender

                             By:
                                ---------------------------------------
                                 Name:  Paul J. Chakmak
                                 Title: Managing Director, CIBC World Markets
                                         Corp., AS AGENT

                             IMPERIAL BANK, as a Lender

                             By:
                                ---------------------------------------
                                Name:
                                     ----------------------------------
                                Title:
                                      ---------------------------------

                             CITY NATIONAL BANK, as a Lender

                             By:
                                ---------------------------------------
                                Name:
                                     ----------------------------------
                                Title:
                                      ---------------------------------

                             BANQUE NATIONALE DE PARIS, as a Lender

                             By:
                                ---------------------------------------
                               Name:
                                    -----------------------------------
                               Title:
                                     ----------------------------------

This Amendment is

                                       4

<PAGE>

approved and accepted as of
the date first above written

MICROSEMI CORPORATION

By:
   -------------------------------
   Name:
        --------------------------
   Title:
         -------------------------

                                       5

<PAGE>

                              CONSENT OF GUARANTORS
                            Dated as of June 25, 1999

         Please refer to that certain Guaranty dated as of April 2, 1999 (the
"Guaranty") executed by the undersigned in favor of Canadian Imperial Bank of
Commerce, as Administrative Agent under the Credit Agreement dated as of April
2, 1999 for Microsemi Corporation (the "Credit Agreement"). Capitalized terms
used herein shall have the meanings ascribed thereto in the Credit Agreement.

         The undersigned have reviewed that certain Amendment of even date
herewith to the Credit Agreement. By their execution hereof, the undersigned
Guarantors hereby consent to the terms of the Amendment.

         By its execution hereof, each of the undersigned Guarantors hereby
represents and warrants that:

                  (i)    this Consent has been duly authorized, executed and
delivered by the undersigned Guarantor and constitutes its legal, valid and
binding obligation enforceable against it in accordance with the terms hereof
(subject to applicable bankruptcy, reorganization, insolvency, moratorium or
similar laws affecting creditors' rights generally and subject, as to
enforceability, to equitable principles of general application (regardless of
whether enforcement is sought in a proceeding in equity or at law)); and

                  (ii)   the representations and warranties contained in the
Guaranty are true and correct as of the date hereof as though made on and as of
the date hereof.

                                       6

<PAGE>

         The undersigned Guarantors hereby further confirm and agree that the
Guaranty is and shall continue to be in full force and effect and is hereby in
all respects ratified and confirmed.

                                           Guarantors:

                                           LINFINITY MICROELECTRONICS, INC.
                                           MICROSEMI CORPORATION - SCOTTSDALE
                                           MICROSEMI CORPORATION - COLORADO
                                           MICRO USPD, INC.

                                           By:
                                              --------------------------------
                                             Name:
                                                  ---------------------------
                                             Title:
                                                   -----------------------

Accepted, Acknowledged and Agreed:

CANADIAN IMPERIAL BANK OF COMMERCE,
as Administrative Agent

By:
   --------------------------------
Its:
    -------------------------------
                                                                  EXHIBIT A

                                       7<PAGE>
                                                                 EXHIBIT 10.85.2

                                SECOND AMENDMENT
                                       TO
                                CREDIT AGREEMENT

                          Dated as of February 14, 2000

         This SECOND AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is among
MICROSEMI CORPORATION, a Delaware corporation (the "Borrower"), the several
financial institutions party to the Credit Agreement referred to below
(collectively, the "Lenders"; individually, a "Lender"), CANADIAN IMPERIAL BANK
OF COMMERCE, as administrative agent for the Lenders (the "Administrative
Agent").

                             PRELIMINARY STATEMENTS:

         (1)      The Borrower, the Lenders and the Administrative Agent have
entered into that certain Credit Agreement dated as of April 2, 1999, as amended
by that certain First Amendment to Credit Agreement dated as of June 25, 1999
(as so amended the "Credit Agreement"; capitalized terms used and not otherwise
defined herein have the meanings assigned to such terms in the Credit
Agreement).

         (2)      The Borrower has requested that the Administrative Agent and
the Lenders make certain amendments to the Credit Agreement.

         (3)      The Administrative Agent and the Lenders are, on the terms and
conditions stated below, willing to grant the request of the Borrower.

         NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree as follows:

         SECTION 1. Amendments to Credit Agreement. Effective as of the date
hereof and subject to the satisfaction of the conditions precedent set forth in
Section 2 hereof, the Credit Agreement is hereby amended as follows:

                  (a)      Section 1.1 of the Credit Agreement is hereby amended
by adding the following definition thereto in appropriate alphabetical sequence:

                  "Maintenance Capital Expenditures" means any Capital
         Expenditures made by the Borrower or its Subsidiaries which are made to
         maintain or restore the condition or usefulness of property of the
         Borrower or its Subsidiaries but which are not properly chargeable to
         repairs and maintenance in accordance with GAAP.

                  (b)      The definition of the term "Applicable Margin" in
Section 1.1 of the Credit Agreement is hereby amended by deleting the word
"December" from the second sentence thereof and replacing it with the word
"January".

<PAGE>

                 (c)      The definition of the term "Fixed Charge Coverage
Ratio" in Section 1.1 of the Credit Agreement is hereby amended by inserting the
word "Maintenance" immediately prior to the words "Capital Expenditures" in the
second line thereof.

                 (d)      Section 7.1.1(c) is hereby amended by deleting the
phrase "as soon as available and in any event within 45 days after the end of
each Fiscal Quarter", and replacing it with "as soon as available and in any
event within 45 days after the end of each of the first three Fiscal Quarters of
each Fiscal Year and within 90 days after the end of each Fiscal Year,".

          SECTION 2. Conditions to Effectiveness. The amendments in Section 1 of
the Amendment shall be effective as of the date hereof, subject to the
Administrative Agent's receipt of the following on or before February 18, 2000:

          (a)    counterparts of this Amendment executed by the Administrative
                 Agent, the Borrower and Majority Lenders;

          (b)    counterparts of the Consent appended hereto as Exhibit A
                 executed by the Guarantors; and

          (c)    such other documentation as the Administrative Agent or any
                 Lender shall reasonably request.

          SECTION 3. Representations and Warranties. The Borrower represents and
warrants as follows:

                 (a)    Authority: Enforceability. The Borrower has the
          requisite corporate power and authority to execute, deliver and
          perform this Amendment, and to perform its obligations under the
          Credit Agreement as amended hereby. The execution, delivery and
          performance by the Borrower of this Amendment, and the consummation of
          the transactions contemplated hereby, have been duly approved by the
          Board of Directors of the Borrower and no other corporate proceedings
          on the part of the Borrower are necessary to consummate such
          transactions. This Amendment has been duly executed and delivered by
          the Borrower. Each of this Amendment and the Credit Agreement as
          amended hereby constitutes the legal, valid and binding obligation of
          the Borrower, enforceable against the Borrower in accordance with its
          terms.

                 (b)    Loan Document Representations and Warranties. The
          representations and warranties contained in each Loan Document are
          true and correct on and as of the date hereof, before and after giving
          effect to this Amendment, as though made on and as of such date
          (unless stated to relate solely to an earlier date, in which case such
          representations and warranties shall be true and correct as of such
          earlier date).

                 (c)    Absence of Default. No event has occurred and is
          continuing, or would result from the effectiveness of this Amendment,
          that constitutes a Default.

          SECTION 4. Reference to and Effect on the Loan Documents. (a) Upon and
          after the effectiveness of this Amendment, each reference in the
          Credit Agreement to "this Agreement", "hereunder", "hereof" or words
          of like import referring to the Credit Agreement,

<PAGE>

and each reference in the other Loan Documents to "the Credit Agreement",
"thereunder", "thereof" or words of like import referring to the Credit
Agreement, shall mean and be a reference to the Credit Agreement as modified and
amended hereby.

                  (b)      Except as specifically amended above, the Credit
Agreement and all other Loan Documents are and shall continue to be in full
force and effect and are hereby in all respects ratified and confirmed.

                  (c)      The execution, delivery and effectiveness of this
Amendment shall not, except as expressly provided herein, operate as a waiver of
any right, power or remedy of any Lender or the Administrative Agent under any
of the Loan Documents, nor constitute a waiver of any provision of any of the
Loan Documents.

         SECTION 5. Execution in Counterparts. This Amendment may be executed in
any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed and delivered shall be deemed to be
an original and all of which taken together shall constitute but one and the
same agreement. Delivery of an executed counterpart of a signature page to this
Amendment by telefacsimile shall be effective as delivery of a manually executed
counterpart of this Amendment.

         SECTION 6. Governing Law. This Amendment shall be governed by, and
construed in accordance with, the laws of the State of New York.

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers thereunto duly authorized, as of the date
first above written.

                         CANADIAN IMPERIAL BANK OF
                         COMMERCE, as Administrative Agent

                         By:_______________________________
                            Name:  Paul J. Chakmak
                            Title: Managing Director, CIBC World Markets Corp.,
                            AS AGENT

                         CIBC INC., as a Lender

                         By:_______________________________
                            Name:  Paul J. Chakmak
                            Title: Managing Director, CIBC World Markets Corp.,
                            AS AGENT

                         IMPERIAL BANK, as a Lender

                         By:_______________________________

<PAGE>

                            Name:__________________________
                            Title:_________________________

                            CITY NATIONAL BANK, as a
                            Lender

                            By:______________________________
                               Name:_________________________
                               Title:________________________

                            BANQUE NATIONALE DE PARIS, as a
                            Lender

                            By:______________________________
                               Name:_________________________
                               Title:________________________

This Amendment is
approved and accepted as of
the date first above written

MICROSEMI CORPORATION

By:____________________________
   Name:_______________________
   Title:______________________

<PAGE>

                              CONSENT OF GUARANTORS
                         Dated as of February 14, 2000

         Please refer to that certain Guaranty dated as of April 2, 1999 (the
"Guaranty") executed by the undersigned in favor of Canadian Imperial Bank of
Commerce, as Administrative Agent under the Credit Agreement dated as of April
2, 1999 for Microsemi Corporation (the "Credit Agreement"). Capitalized terms
used herein shall have the meanings ascribed thereto in the Credit Agreement.

         The undersigned have reviewed that certain Amendment of even date
herewith to the Credit Agreement. By their execution hereof, the undersigned
Guarantors hereby consent to the terms of the Amendment.

         By its execution hereof, each of the undersigned Guarantors hereby
represents and warrants that:

                  (i)      this Consent has been duly authorized, executed and
delivered by the undersigned Guarantor and constitutes its legal, valid and
binding obligation enforceable against it in accordance with the terms hereof
(subject to applicable bankruptcy, reorganization, insolvency, moratorium or
similar laws affecting creditors' rights generally and subject, as to
enforceability, to equitable principles of general application (regardless of
whether enforcement is sought in a proceeding in equity or at law)); and

                  (ii)     the representations and warranties contained in the
Guaranty are true and correct as of the date hereof as though made on and as of
the date hereof.

<PAGE>

         The undersigned Guarantors hereby further confirm and agree that the
Guaranty is and shall continue to be in full force and effect and is hereby in
all respects ratified and confirmed.

                                           Guarantors:

                                           LINFINITY MICROELECTRONICS, INC.
                                           MICROSEMI CORPORATION - SCOTTSDALE
                                           MICROSEMI CORPORATION - COLORADO
                                           MICRO USPD, INC.

                                           By:_______________________________
                                             Name:__________________________
                                             Title:_________________________

Accepted, Acknowledged and Agreed:

CANADIAN IMPERIAL BANK OF COMMERCE,
as Administrative Agent

By:________________________________
Its:_______________________________

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