ZW and TW whistle short

[lionelsoni]

That does indeed sound like a short circuit.

The first thing the whistle control does is to connect the output terminal to a point which includes the 5-volt compensating winding and the rectifier in series with the wiper on the variable-secondary winding.  Then it disconnects the output terminal from the variable-secondary winding.  The disconnection has to happen almost simultaneously with the connection.  Otherwise the rectifier is connected directly across the 5-volt winding.  Perhaps the switch is bent in such a way that this disconnection does not happen as quickly as it should, or not at all.

The switch wiper has two ends, one of which is bifurcated.  This double end moves from one large contact to another as you rotate the switch, to make the first connection.  Then the single end moves off its small contact for the disconnection.  (As the switch continues to turn, the single end reaches another small contact, which puts a 1.5-ohm resistor in parallel with the rectifier.)  Perhaps from this discription you can see whether the switch is doing its job correctly and fix anything that is bent.

[J. Daddy]

I suspect that the problem is actually an open circuit, as Jim describes.  But I would like to know why he thinks that it is a short circuit, to see whether he has a reason to think so.

I believe its a short cuircut because the ZW lets out a low hum, and the green light on the transformer dims.....but your right... sometimes it is an open circuit as well, depends how far the button is cycled forward.

[lionelsoni]

I suspect that the problem is actually an open circuit, as Jim describes.  But I would like to know why he thinks that it is a short circuit, to see whether he has a reason to think so.

[Anonymous]

When I had this problem with a ZW, the cause was the contacts on the controller lever were not touching their appropriate points.  So when I pushed the lever to the whistle position, I lost power to the track.  When the lever was released, power was restored.  The solution was to slightly bend the contacts on the lever.

[lionelsoni]

What is the evidence for a short circuit?  Do the other outputs drop out at the same time?

[J. Daddy]

 

It appears that you have had the ZW at least partially disassembled, if you replaced the power cord.  When you undo the four top screws and lift the casing off, you should see a circular disk on each side near the direction/whistle buttons.  They are about the size of a fifty-cent piece.  They are held in place by a rectangular "speed-nut".  The speed-nuts can be removed and then the rectifier disks.  While I haven't had to replace mine, it looks like an easy project.  I believe parts shops, such as The Train Tender, carry these disks.  Good luck and I hope this works for you.

Thanks for the update... but it seems maybe its the locomotive? I bought an 2006 F7 A-B-A and everytime I hit the whistle button it changes direction as well. Is this the characteristic of the TMCC locomotives operated with a post war transformer? I think I am still going to take it apart and check for the short, but I am wondering if maybe I should not be operating this A-B-A with a post war transformer....

[initagain]

 

It appears that you have had the ZW at least partially disassembled, if you replaced the power cord.  When you undo the four top screws and lift the casing off, you should see a circular disk on each side near the direction/whistle buttons.  They are about the size of a fifty-cent piece.  They are held in place by a rectangular "speed-nut".  The speed-nuts can be removed and then the rectifier disks.  While I haven't had to replace mine, it looks like an easy project.  I believe parts shops, such as The Train Tender, carry these disks.  Good luck and I hope this works for you.

[J. Daddy]

Thanks for the heads up. I have not taken it apart yet and last time I did I just replace the cord on the ZW it looked very busy in this area and it worked fine so I did not mess with it. The left hand whistle function works fine, and yes, the direction button works fine. Just the Whistle function shorts or sometimes does not activate at all...so what does the rectifier disc look like?

[initagain]

 

Here is a suggestion.  I'm not sure about the TW, but on a ZW the direction/whistle buttons are set such that if you push forward the whistle activates, and if you pull backward, the locomotive e-units cycle to cause the forward-neutral-reverse actions.  I wonder if someone has jigged the wiring inside, such that these functions are reversed.  Did you try the direction function, and if so, does IT work properly?  If it DOES, but the whistle function doesn't, if might be that the rectifier discs (one for each of the two controls) need to be replaced.  It's a little unusual for both discs to malfunction at the same time, but it's possilbe.  Try the other ZW circuit that is controlled by the other direction/whistle button.  If it works OK, then I would suggest that the rectifier disc in the malfuntioning circuit might be the problem.

[RRCharlie]

My thought would be to check the whistle relay and wiring for a bare wire which might be causing the short.

 

[J. Daddy]

I have a post war ZW and TW that both have the original activation buttons, however when I use them the power shorts out and the locomotive changes direction instead of the whistle activating... when I take them apart what should I look for? Ironic that they are very different in activation but have the same fault....