Multimeter Troubleshooting Guide

Multimeter guide troubleshooting

This guide can assist you in diagnosing potential issues with your decoder or installation. These basic checks can be performed to diagnose a wide variety of simple issues you may be having with a decoder installation.

Please note: Continuity checks that include the rails must be performed with one lead connected or touched to the rail.

Any resistance measurements including continuity MUST be performed with the power OFF. 

Check resistance/continuity for the following:

  • Left Rail to Right Rail
  • Orange to Grey (motor connected)*
  • Orange to Grey (motor disconnected)
  • Left Rail to Orange
  • Left Rail to Grey
  • Right Rail to Orange
  • Right Rail to Grey
  • Speaker contacts (speaker disconnected)

None of the above tests should read 0 or near-zero.

*Orange to Grey with a motor connected should read between 50 and 200 Ohms for a typical HO-scale motor. A reading below 50 or near-zero indicates a shorted motor or wiring.
Orange to Grey with the motor disconnected should be a non-zero value of approximately 20K Ohms. 
Speaker itself should read Between 7.2 and 8.8 Ohms. If less than or greater than these numbers, the speaker has failed or is failing. 

Check resistance/continuity for the following: 

  • Left Rail to Power Pickup on decoder
  • Right Rail to Power Pickup on decoder

These readings should be near-zero and not fluctuate.

Check DC voltage for the following:

  • Blue wire to ground
  • Orange to Grey (this test must be done with the motor disconnected) Gradually increase the speed step. You should see the DC voltage increase from 0 to ~12V. Reversing direction will also reverse the polarity of this reading.

Check AC voltage for the following:

  • Left Rail to Right Rail

Voltage measurements are to be performed with power applied to the engine.


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