736 slows to a crawl when Railsounds whistle in tender is activated by ZW

Switch to the other(A or D) outside handle to see if the problem follows the ZW whistle circuit or the train.

It sounds like the resistor that is part of the ZW transformer's whistle control circuit is not being switched into the circuit as it should be.

If so, trying the other side may produce the same results if it was "rebuilt" incorrectly.

(Hopefully not)

Anyone rebuilding ZW's now days will install diodes instead of the old disc which eliminates that problem. correct me if I'am wrong…..guy's. I would think you can fine someone in Texas that can do that.

If I remember correctly on the old ZW when you activated the whistle there was a circut that cut in that would increase the power to help compensate for the whistle motor.  It sounds like that that circut is not working.  A diode or old style rectifier disc would not meffect this.

Does the whistle blow? I think there should be a 5volt boost winding engaging also. My PW stuff increases in speed when the control is hit right if not running an air whistle tender. Could the circuit be wired too bypass this boost? A short in the 5v, or not making the boosted connection? Switching control sides is the right start. 

If the five volt winding was open, the train would stop. The winding is inserted in series with the rest of the circuit.

If the rectifier (diode) was shorted the train would not slow down, and the whistle would not blow. In this case, the train should speed up, due to the insertion of the five volt compensating winding.

When the resistor is open, the train slows way down because the purpose of the resistor is to allow most of the AC current to bypass the rectifier. Without this resistor, the voltage is greatly reduced.

Is it possible that someone rebuilt the ZW and installed the wrong diodes in it?

The diodes are suppose to be "anode to case" and if the wrong one was used could be causing the problem.

OR used the 6 amp diodes which are to small to be used in the ZW's!

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quote:

The diodes are suppose to be "anode to case" and if the wrong one was used could be causing the problem.

 

OR used the 6 amp diodes which are to small to be used in the ZW's

I don't see how either of these issues could cause the described problem.

If the opposite polarity diode is used, Postwar horns/whistles would be unaffected. Polarity sensitive Modern era stuff (horns/bells/whistles) might not work, but the train should not slow down.

If the diode capacity is too low, it could overheat. In my limited experience, they might short out, which as I wrote above, would actually make the train run faster.

I guess the train might slow down if the diode was to overheat and open the circuit.

I suspect a problem with the ZW transformer. However try it with another engine that has a horn or whistle installed and see what happens. If both engines don't do right then the transformer is the problem.

Lee Fritz

If he has another, this would be the best test yet if the two sides share the 5v of the zw.

 Fresh thought while writing the crud below....Or remove the tender from the track, and run the loco alone, or hook up a lighted car. You should see a boost in speed or light from the whistle circuit when activated! If it slows, or dims its in the transformer.

It is remotely possible the tmcc whistle wont work with a PW control. I have had 2 tmcc Berks that wouldnt whistle from my KW, 1033s, or a pre-war Z with external controller, but both worked with any modern unit. One is a C&O Kanawha, but basically another Berk. Other tmcc have all worked fine. My modern whistle controls/transformers are smaller units and not one will operate a post war air whistle well. They try, but lack of 5v boost is really missed on my old stuff. 

It might not make a difference in respect to the severe slowdown, but if reversing the leads off the zw, one way it would cause the bell to chime, the other the whistle to blow. It seems to me there are semi-normal conditions where things are wired to give a 5v reduction on the whst/hrn control  to avoid run away spurts of speed to short trains, but Im not really "up on that".

 While it doesn't take much offset power to hold a relay open, or to run a already spinning whistle motor, drawing the relay open against a spring, and starting the air whistles motor from a dead stop took more. So they used a switch that quickly used the sequence of "off then 5v then 1.5v". Modern chip style electronics do a similar job using much less power so no 5v boost is needed.The PW 5v boost often boosts tmcc more that conventional.