Mainframe Assembler Developer

Looking for a high-impact role where your legacy expertise bridges the future of retail payments? We are seeking two Principal Mainframe Assembler Developers (15 years) to lead a business-critical Fuel Pre-Authorization project in partnership. In this role, you will re-engineer the 0120 transaction workflow for near-real-time processing, while serving as a vital technical anchor ensuring system stability during our enterprise cloud migration. If you have deep Connex and Xpediter expertise and want to own a high-visibility project slated through Q1 2027, let's talk.

Core Development & Optimization: Modify and develop low-level Mainframe Assembler (BAL) code to update the 0120 automated fuel dispenser transaction.

Migration Bridge Support: Maintain, troubleshoot, and support critical, ongoing mainframe operations to ensure business continuity while the organization executes its cloud migration strategy.

Real-Time Transaction Logic: Implement architecture changes to adjust pre-authorization amounts and update real transaction amounts in near real-time, ensuring proper processing and transaction reversals.

System Integration: Collaborate closely with internal teams and to align client-side changes with 0120 confirmation advice for a synchronized release.

Testing & Debugging: Utilize Xpediter to debug complex Assembler code, isolate defects, and support rigorous unit, integration, and regression testing.

Requirement Refinement: Actively partner with client teams currently flushing out requirements, providing senior-level technical insights to augment their current efforts.

15 years of experience in Mainframe IBM Assembler (BAL) development.

Connex Platform: Deep hands-on experience working within the Connex switching/payment processing environment.

Debugging Tools: Proven expertise using Xpediter for mainframe debugging and troubleshooting.

Payment Systems Knowledge: Strong understanding of financial transaction messaging, specifically automated fuel dispenser (AFD) workflows and pre-authorization/clearing cycles.

Professional Attributes & Context:

Migration Experience: Previous experience working in environments undergoing a mainframe-to-cloud migration is highly preferred. You understand the unique challenge of keeping the legacy engine running smoothly while the new one is being built.

Experience with high-volume, near-real-time transaction processing systems where data integrity and zero downtime are paramount.

Ability to hit the ground running with ambiguous or evolving requirements.

Preferred Qualifications (Nice to Have)

Familiarity with ISO 8583 messaging standards.

Experience with phased, large-scale migration or deployment strategies in a banking or retail fueling environment.

Equal Opportunity Employer: Race, Color, Religion, Sex, Sexual Orientation, Gender Identity, National Origin, Age, Genetic Information, Disability, Protected Veteran Status, or any other legally protected group status.

At Randstad Digital, we welcome people of all abilities and want to ensure that our hiring and interview process meets the needs of all applicants. If you require a reasonable accommodation to make your application or interview experience a great one, please contact

Pay offered to a successful candidate will be based on several factors including the candidate's education, work experience, work location, specific job duties, certifications, etc. In addition, Randstad Digital offers a comprehensive benefits package, including: medical, prescription, dental, vision, AD&D, and life insurance offerings, short-term disability, and a 401K plan (all benefits are based on eligibility).

This posting is open for thirty (30) days.


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Qualified applicants in San Francisco with criminal histories will be considered for employment in accordance with the San Francisco Fair Chance Ordinance.



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We will consider for employment all qualified Applicants, including those with criminal histories, in a manner consistent with the requirements of applicable state and local laws, including the City of Los Angeles' Fair Chance Initiative for Hiring Ordinance.

Salary : $70