Troubleshooting E-Stop and Interlock Circuits on PCBA Auto Insertion Machine

Troubleshooting E-Stop and Interlock Circuits on the Machine

Instructor Guide


Troubleshooting E-Stop and Interlock Circuits

On the Machine

Estimated Time


3 hours

Prerequisite setups and materials
These setups and materials are required before this module is presented:

  1. IM8ECTT Study Guide (1 per trainee)
  2. Machine in operating condition




The E-Stop and interlock circuits on Universal‘s products are designed to ensure that axis operation can occur only when these safety circuits are satisfied. The E-Stop and Interlock safety circuit is hard-wired and will perform its function independent of machine software.

In this lesson, you will look at the E-Stop and Interlock safety circuit in detail. Once you understand how it works you will get some practical experiences in troubleshooting this circuit.

Lesson Objectives


  1. Trace E-Stop/Interlock circuit at machine and check the Interlock system with the job aid provided.
  2. Given a machine with a fault in the E-Stop/Interlock circuit, locate and repair the fault using information in the study guide and the MSD.

Instructional Strategy for the module

  1. Discuss European Safety Standards
  2. Discuss sequence of events of E-Stop and Safety interlock and how they relate to power distribution
  3. Trace the troubleshooting steps:
  • Before E-Stop
  • After E-Stop
  • Interlock Made
  • After Start






European Safety Standards

European Safety Standard


Universal‘s E-Stop and Interlock circuit is in compliance with European Safety Standards, which include the following requirements:

  • Use of redundancy (i.e., two mechanical relays to disable dangerous voltages)
  • Use of contacts which move together and are positive guided (no contact can be in the de-energized state if one contact is stuck in the energized state)
  • All relays must have a normally closed contact used to test the relays.

the E-Stop and Interlock Circuits



This activity is intended to give you some practical experiences in troubleshooting the E-Stop and Interlock Circuits on a machine. In this activity your instructor will put one or more bugs in the machine E-Stop and Interlock circuits. Your job is to find and fix the bugs so that the machine is returned to normal operation.



  • High voltage is present on the machine when power is turned on. Take great care when troubleshooting the electrical assemblies in the machine!
  • Whenever possible, never reach into an electrical assembly when the machine power is on.
  • Use extreme caution when connecting or disconnecting a multimeter. When the situation warrants, use test probe clips to connect the multimeter to test points with power off at the assembly*, then apply power to read the meter; and turn assembly power off before disconnecting the meter.


*An E-Stop or circuit breaker can often be used to remove assembly power.



  1. Working in a small group (never alone), locate and repair the bugs put into the machine by the instructor. The machine must be returned to normal operating condition when you have completed your work.
  2. It is strongly recommended that you follow a sequence when troubleshooting the E-Stop and Interlock system. The Troubleshooting Flow Chart on the following page should help you determine what part of the subsystem is not working.


When looking for machine-specific information, always refer to the electrical diagrams that come with the machine on which you are working.



Simplified Schematic of the Interlock System for Single Head Axial Machines

Simplified Schematic of the Interlock System for 6241FSimplified Schematic of the Interlock System for Dual Head Axial Machines

Simplified Schematic of the Interlock System for 6380A




Trace signals in the electrical schematics to answer the following questions.

  1. 24VAC is delivered to 4TB at pins 31 through.35 and 91 through 95. Find where pin 31 is connected to

            5FU-Side (SHT2)

This question refers to the drawings for PS1, trace it from the secondary side of 2T (24V SEC) and is tied in with 5FU (sheet 2)

  1. What happens when the contacts between pins 1 and 2 close in both 22CR and 23CR?

56VDC is supplied to 4TB

Connects 56 VDC from secondary of 1T to 4TB distribution point to X-Y table motors.

  1. When you suspect that the 24VAC or a DC voltage is missing from the machine, which electrical schematics should you use to troubleshoot the machine?

    the “ELECT DIAG, Power chassis” schematic

Ask students: You lost 24VAC, where it’s generated from? (the inserter’s power chassis, PS1.) Where do you find that drawing? ELEC DIAG, Power Chassis.



E-Stop Circuit Active















  • Using the simplified schematic, individually trace and describe the E-stop and interlock circuit of an IM8 machine
  • Work in a small group, locate and repair the faulty E-Stop and Interlock circuits. Use your notes, flowchart and MSD.


Instructor notes: the following table lists suggested bugs to simulate an E-stop and Interlock circuit problem.



Simulation Method

24VAC to PS is lost Remove 7FU, 4FU, or 5FU
21CR can’t be energized Disconnect X1 and X2
Relay problem Disconnect at contact 21 or 22 of 22CR and 23CR (Interlock system will not enable)
Cannot get out of interlock condition Remove 6PL jumper plug at the back of PS1
Cannot get out interlock condition Remove wire T12 from 21CR relay block
No air to cylinders Disconnect dump valve connector


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