Troubleshooting - 4QD - Electric Motor Control

Troubleshooting

If you can’t get your motor controller to work, we’ve found that following these troubleshooting steps often helps to find the problem;

General problems:

  • As a starting point measure the voltage across the battery terminals.
  • Now measure the voltage across the controller B+ / B- terminals – ideally do this under load,  is it the same as the battery voltage? if not check for faulty joints.
  • Is the “high pot lockout” feature activating? [not Porter or DNO].
  • Are the fuse tracks on the circuit board ok? see the manual for details.
  • Has the pot been replaced? We consider pots to be a bit like car brake pads, they have a spring loaded metal arm which presses on a carbon track which will eventually wear out and cause odd behaviour especially at low speed.
  • Are the control cable plugs in good condition? The example in this picture caused all sorts of intermittent problems as the internal pins shorted out ….

poor IDC connection

 

 

They’re cheap to replace, and can be ordered here.

 

 

 

  • One last point, the majority of mosfet failures are due to electrical noise from the motor brushes. We strongly advise fitting suppression components  and making sure your installation follows these guidelines.

If you need help with troubleshooting we’re happy to help but please before you contact us, download and complete the relevant fault finding sheet [see below], it will help us get you running again a lot faster.

We’ve recently created a controller test board, it works by temporarily taking the place of the normal control wiring, and helps to identify and isolate problems. These are available free of charge to all model locomotive clubs, are available for purchase here, and can be loaned if required.

Here are some some model specific fault finding guides…..

DNO, Pro, and VTX models

  • Print off the relevant fault finding sheet…. DNOPro-150Pro-120 these list the voltages you should expect to find and give an indication of the problem if they are wrong.
  • Remove the controller cover.
  • Check the fuse tracks [see manual for location].
  • Now plug the control cable back in, then check the following voltages on the back of the grey 6 way connector. Note: for the DNO take care not to press the PCB so that it shorts on the metal heatsink.

troubleshooting

Wire colour Voltage [with respect to B-] If it’s not….
Green 0 Wiring fault or blown fuse track
Blue 0 – 7V [Pro-150=5V] changes with pot position Wiring or pot fault
Red Approx 7V [Pro-150=5V] Wiring or controller fault
Black 0 or B+, changes with reverse switch Wiring or switch fault
White 0 or B+, changes with ignition switch Wiring or switch fault
Yellow B+ Wiring fault or blown fuse track

Here’s a video showing how to do this on a  Pro-120

4QD-200 / 300 models

  • Check that the various jumpers on the control board are set correctly for your application.
  • Check that the under voltage protection pot is set correctly for your battery.
  • Check both the fuse tracks, there is one per board, see here for their location.
  • Now print off the fault finding sheet,  this lists the voltages you should expect to find and gives an indication of the problem if they are wrong.
  • Check the following voltages on the pins of the grey 6 way connector on the top board.

testing the 4qd-300

Pin letter [wire colour] Voltage [with respect to B-] If it’s not….
A 0V with ignition off,             11V with ignition on [0V if inhibit activated]
B 0V with ignition off,             11V with ignition on Wiring or controller fault
C [Black] 0 or B+*, changes with reverse switch [* can be 11V if alternative wiring used] Wiring or reverse switch fault
D [Red] Approx 11V Wiring or controller fault
E [Blue] 0 – 11V, changes with pot position Wiring or pot fault
F [Green]  0V  Wiring fault or fuse track blown

Also check the following voltages on the grey 4 way connector on the bottom board

Pin letter [wire colour] Voltage [with respect to B-] If it’s not….
A
B
C [White] 0 or B+, changes with ignition switch Wiring or switch fault
D [Yellow] B+ Wiring fault

We also have some general fault finding tips for the 4QD series here, and some instructions on how to test the base board and MOSFETs here.

Porter 5 / 10

  • First print off the fault finding sheet.. this lists the voltages you should expect to find and gives an indication of the problem if they are wrong.
  • Remove the controller cover, plug the control cable back in, then check the following voltages on the pins of the grey 5 way connector on the board.
Pin letter Voltage [with respect to B-] If it’s not….
A 0 – 0.5V Wiring or controller fault
B 0 – 0.5V Wiring or controller fault
C 1-4V, changes with pot position Wiring or pot fault
D 5V Wiring or controller fault
E 5V Wiring or controller fault