Thanks for all this helpful advice, Mike. Here are some quick answers to the questions, before I go and try out some of these tests after dinner...
1) Make sure that the red leads from the transformers are connected to A) the catenary and B) the centre rail (lead) and that the brown leads are connected to the track. Are you using a common lead for both transformers or do you have separate power supply tracks for each transformer? If using accessories, such as lights, signals or switches, how are these connected to each transformer? If you have accessories, disconnect each accessory one at a time to determine if this is the cause of your issue (by elimination).
>> I checked that all red wires are connected. I have two transformers, the brown leads are connected to each other, and the one red to the centre rail, and the other red to the catenary. I run all lighting on the one yellow, and all switches and signals to the other. I'll try seeing if any of the accessories are causing the toruble!
2) Do both locomotives have pantographs or is one a diesel or steam engine? If both have pantos, what happens if you switch power source for each locomotive?
If yes, are you running both locomotives with pantographs raised, even the one that is powered from the rails? If yes, lower that panto and test to see if that solves the problem.
Make sure that the power selection switch on both locomotives is correctly set to the selected source and not halfway between the two.
>> One is running on pantographs (SBB Ae 3/6), the other is a steam engine (DB series 38 -- my favorite, since I remember trip with that loco as child in the 1970s). I checked that all these were set correctly. I switched over the Ae3/6 to the centre rail, and it did not work either. So, I've eliminated the locos as the source of the problem.
3) What happens if you connect only one transformer at a time? Before testing, make sure that you disconnect the other transformer from the wall and from the track.
If there is a potential polarity issue, connecting only one transformer should solve that issue on that part of the layout. Perform the same test after disconnecting that transformer and reconnecting the other one to the track leads. If both work separately, it is likely that the issue is due to polarity.
>> I tried testing one at the time, but never thought to disconnect one from the wall socket. I'll do so.
4) What happens to a coach that is equipped with illumination powered from the rails? Are the lights on when there is power or does it display the same problem as the locomotive?
>> Coach lights to the same as the locomotive: no power at all, until I switch back, and then they light up very brightly. I eliminated the coach lights, and am certain that those are not the problem.
5) I forgot to ask which tracks you are using, the metal (M) or plastic (K) ones? The older M track catenary masts have metal bases that contact the ground and can short out if the live comes into contact with the ground. The catenary mast mountings for K track have plastic clips which prevents this.
>> All wonderful old-fashioned M tracks. If there was a short with the catenary, wouldn't the electric loco then not work as well?
6) The next thing that I would check is to inspect the catenary masts to see if any of the masts are warm after use. This would be an indicator of a possible short between one of the masts and the track
>> I'll check that.
7) If using K track, you should check the connection clips at the track ends to ensure that there is no short that affects the third rail circuit. If you performed test #2 and everything was ok with just one transformer, you can ignore this.
and lastly, If you don't do it for more than a few seconds, take the brown and red leads from the transformer connected to the track and swap them. That should have the same result as inverting the polarity at the plug. If everything works, then reversing the polarity at the plug should solve the issue.
>>> OK, I'll go off to my attic and try all this! Thanks for the advice, and I'll come back with a full report.
