Testing continuity between pickup rollers on locomotive?

Most better DVM’s have a built in continuity tester, when a circuit is complete, it beeps, or rings,....fastest and easiest way to test continuity,.....if the rollers are linked, it’ll beep, if they’re not it’ll show an open ( no beep)

Pat

You can use a meter, but I'm usually too lazy to get it out.  I put about a 1" (length not critical) piece of masking tape on the center rail and slowly run the locomotive over it.  If it stops when one of the rollers is on the tape, then the other roller (the one still on the live rail) is not picking up.

@Paul Kallus posted:

I suspect my newer MTH bipolar locomotive (has two pickup rollers) has a disconnected pickup roller (all wires that I can see are attached) because it is stalling on each and every Ross switch (I have another MTH bipolar that makes it through just fine and from operating previous bipolars I know they can make it through. I have a Cen-Tech digital voltmeter from Harbor Freight. If I test the continuity by placing the leads on each pickup roller, it should read close to zero Ohms, right? Would that conclude that both pickup rollers are connected and therefore rule out one of them as the problem? If so, that would clue me to that its a grounding wheel(s) problem. Do I have that about right?

Yes, you have that right.

The inexpensive meters will often not read all the way down to zero. Set the meter on 200 ohms. Cross the meter leads and see what the meter reads (hey, that rhymes!). On my meters, they tend to read in the 3-4 ohm range with the probes touching. So you know that 3-4 ohms, or whatever your meter reads, equals zero in real life.

If you get no continuity between rollers, try the arms that hold the rollers. The pickups could be connected internally, but there could be dirt/crud/burnt oil inside the roller.

I have an older Bipolar and there was no continuity between the rollers. I always assumed it was a wiring error in China. I determined this by energizing only one roller at a time on a roller stand. I added a wire inside the loco to connect the rollers and it has been running ever since.

Thanks for the tips. I tested the newer Bipolar and there was no continuity between the pickup rollers, which I suppose explains the stalling out over the switches. I removed the ends of the bipolar - and then removed the two screws which recess into a plastic insert and where that insert fits into a hole in the diecast metal frame (the pickup roller is attached to one of them whereas the other goes directly to the frame) and reversed the wires. This enabled continuity between the pickup rollers and the train now goes through the switches. Note that if you do this, you must disconnect the wiring harness.

However, in reversing those two wires I noted that there's now no continuity between both side truck frames or outside wheels of the engine, i.e., left facing front and right facing front do not have continuity between the outside wheels. This seems impossible to me because I would think the engine would not run at all? How can the pickup rollers now be connected and the grounding wheels from the left side of the unit not have continuity with the right side of the unit?

The DCS/DCC switch is set to DCS, and I don't think the train would add to DCS if the switch was wired backwards?

@Bob posted:

You can use a meter, but I'm usually too lazy to get it out.  I put about a 1" (length not critical) piece of masking tape on the center rail and slowly run the locomotive over it.  If it stops when one of the rollers is on the tape, then the other roller (the one still on the live rail) is not picking up.

Bob,  Great tip!  I wish that I had thought of this a long time ago.  NH Joe

I suppose I should've put this thread under MTH...regardless, as an update this engine has problems...I returned all wiring back to original and instead of stalling over switch, am now getting a dead short. Four hours of my weekend wasted on this engine. Now, I just have to get a hold of either MTH, the selling dealer, or an authorized MTH repair...hopefully one of the first two will stand tall.

Check each roller to make sure they spin freely. I’ve had several engines thinking the same as you. I had to spread the roller holders and applied oil to get them to spin freely. Problem solved. Quick fix. Hopefully that’s your problem. Also check for dirt buildup on each roller.