Customer Vending Machine Auto-Vend Diagnosis

Problem

The customer machine automatically triggered one selection when credit reached $0.50. Possible causes included the selection motor path, bypass wiring, selection logic, controller behavior, or the credit system.

Description

What I built or investigated

I reproduced the trigger condition, disconnected the affected selection motor to test whether the symptom followed that circuit, measured the two-wire display behavior, and evaluated the bypass/free-vend hypothesis without replacing parts blindly.

Iterations

The work did not happen in one jump.

1. 01

   Confirmed that the unwanted vend occurred at the same credit threshold.

2. 02

   Disconnected the affected selection motor and verified that the automatic vend stopped, narrowing the fault to that path.

3. 03

   Measured both DC and AC behavior on the two-wire display while investigating how the changing display information was carried.

4. 04

   Considered the bypass/free-vend switch hypothesis and whether unplugging it should remove the symptom.

5. 05

   Completed the agreed diagnostic scope and quoted an optional free-vend conversion separately.

6. 06

   Preserved customer privacy and did not publish unrelated photos as evidence of the service call.

Result

Where the project landed

The paid service call produced a defensible fault-isolation record and a clear next-step option. The customer declined the optional conversion, and the work remained within the agreed scope.

Lessons

What carried forward

• A repeatable trigger condition is valuable diagnostic evidence.
• A disconnect test is useful only when it answers a specific circuit question.
• Customer choice, privacy, and scope control are part of a professional repair.