The ZW whistle switch works by putting a primitive diode in series with the power to the track while at the same time switching to a step-up winding on the transformer that bumps the voltage to compensate for the load of the whistle motor. After 70+ years it's very possible the electrical contacts in the switch are worn, dirty, or otherwise out of spec. A quick easy repair would be to clean the switch contacts and see if that makes a difference.
Another issue is the 1940s era primitive rectifier disc the transformer uses to create DC. If you havn't done so, I reccomend replacing them with stud-rectifiers which for the most part are drop-in late 20th century diode replacements. I use an 1N1184r but there are a couple of sellers on eBay that sell them complete with instalation instructions. The diode replacement provides a cleaner DC signal which leads to a better performing whistle motor.
I have repaired a lot of ZW's back in the 80's, cords, circut breakers, and rollers, but I have forgotten quite a bit as I have been inactive repairing trains for many years. I am back at it getting a major layout built for my grandkids. One of my ZW's and my various whistle tenders are having problems. I have isolated what seems to be the best working tender a 2671WX to do a series of tests with the problem ZW. The tender works normally with the associated 736 on the test track and a 1033. It whistles normally in neutral and when running forward and backward with the 1033. With the ZW not so much.
With just the 2671WX on the test track and testing whistle controls, the ZW, on both the A and D side when you push the whistle switch full travel, you get no whistle engagement, but as the switch travels back to center position, the whistle chirps. When you move the whistle switch about 1/2 way, the whistle sounds normally.
With the 736 and 2671WX on the test track and the ZW being tested, on the A side when powered up, with the e-unit in neutral, moving the whistle control full travel the whistle chirps and the e-unit cycles and the loco goes from neutral to reverse as the switch moves back to its center position. With the 736 traveling forward and with full travel on the whistle switch, the e-unit cycles to neutral stopping the 736, and sometimes it cycles twice to reverse. On the D side we get the same behavior.
I'm pretty sure the 2671WX whistle tender is working normally. I have no experience or recollection of what the symtoms are for failed or failing rectifier disks. What are the symptoms they are failing? Visual inspection shows no apparent signs of heat or burns.
I did clean the whistle switch contacts with some 600 paper and contact cleaner. Seemingly no help. I also observed how the two switch spring contacts, and the two spring contact arms appear to be contacting and releasing on and off their contacts on the switch assemblies and they seem to sequence as they should as described in the original Lionel service guide for Multi-control Transformers.
So I need to learn some more about how this all works and some ideas for further test and repair. Thanks in advance for all your help.
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