No voltage boost when whistle activated TW

Since the whistle works, the rectifier disc is good. Recommend to replace the rectifier disc as a normal service item.

If you are not getting the voltage boost when the whistle is activated, check for continuity through the switch contacts and through the 6 volt transformer winding.

See here for the schematic, and here for the wiring view.

Larry

I am not a friend of the TW. They are problem prone. Try this, remove the cover and replace the handles. Now try to blow the whistle. If it works OK now, the whistle handle has warped from the heat and preventing the handle from completing the arc to engageing  the boost voltage.

Larry - There seems to be continuity in the 6 volt circuit. If I do end up replacing the disc I'll probably go with a 6 amp diode.

Chuck - Yes, the handle is warped a bit but there is no interference with the case. I did remove the case and check per your suggestion but results are the same.

Thanks to you both for the input!

Before I posted I did a forum search. I found a thread where someone indicated that the resistor wire "dampens" the track voltage until needed for the whistle circuit (if I understood correctly what I was reading). So what is the function of the resistor wire (part#1033-103) and does anyone know the ohm value for this part?

The resistor associated with whistle is designed to come in after the whistle relay has picked up. It allows some current  to bypass the rectified disc to take some of the load off of it. The whistle needs about 5 VDC to pick up but only about 1 VDC to stay closed. The resistor splits the current between the rectifier disc and the resistor. I believe the resistor is 1.5 ohms. 

Probing with an AC meter should identify where you are loosing the  5 volt boost.  Interesting to see what the voltage across the rectifier disc is. 

David - Thank you for the explanation of the whistle circuit resistor and what it does. Should the resistor wire be disconnected to get a proper ohm reading? Otherwise I'm seeing about a 0.4 ohm reading, which looks to me like I'm just checking continuity.

I'd like to check the voltage across the rectifier disc but not sure exactly how to do this. Is this a simple procedure?

When the lever is fully thrown the resistor is in parallel with the rectifier.  This allow some ac to bypass the rectifier.  Without it you would simply have a half wave rectified dc supply - a higher dc component and a lower ac component.

This circuit is based on the inefficiency of selenium rectifiers and the characteristics of the traditional motor and whistle circuit.  (Also these rectifiers release toxic fumes if they fry.)  You should replace with a modern diode.  Recheck the results after you do this.

From the service manual section for the 1033 transformer, “The function of the nichrome resistance wire across the rectifier is to regulate the holding voltage applied to the whistle relay.  Its resistance should measure 1.5 ohms.  Lower resistance means a proportionally lower d.c. holding voltage.  A higher resistance means a greater load on the rectifier disc.  If this resistance wire is loose or broken the entire output voltage of the transformer is applied to the rectifier whenever the whistle is blown.  This condition will quickly overheat the rectifier and will result in permanent damage to the disc. Check the resistance wire carefully for poor connection.”  The resistance of the resistance wire can be checked with out disconnecting it. One end of the wire is connected only the whistle switch is operated.  So if the whistle switch is not operated the resistance wire is not in any circuit  

To check the voltage drop across the rectifier you would need an AC volt meter. The rectifier disc needs a load to conduct properly, so the test would need to be done with a train running.  Connect one lead of the meter to the A post. With the whistle blowing touch the other probe to the rectifier disc connection on each side of the disc.  Subtract the two readings and the difference is the voltage drop across the rectifier. 

I just use the DC setting and peak hold on my meter. No peak hold, you have to do the math above as the voltage is pulsed positive (pulsed dc) and the reading will bounce or scramble(digital)

Thanks to all for your help! I carefully tested the resistor wire with three different meters and get a reading of 2.0 to 2.1 ohms. Not sure if this amount of variance would cause my issue or not.

In the meantime I'm going to replace the disc with a 6 amp diode and see what happens. I will post the results later.

Well, this is somewhat embarrassing but I did track down the problem. It turned out to be a very power hungry PW whistle motor! After removing the (working) rectifier disc and cleaning up the stud, retainer clip, disc, and bracket, I reassembled the transformer. The whistle again worked fine but the locomotive still slowed down.

Now I'll be the first to admit that electricity is sort of a "black art" to me but after studying the schematic, it dawned on me to check the A-U voltage while activating the whistle control. DUH! Sure enough, I saw a voltage increase of just over 6 volts. I retrieved another whistle tender from the stash and all is well.

The faulty whistle motor, from a 2671 tender, apparently had a slightly bent armature shaft but that's a story for another time.

Again, thank you all for your help and suggestions! If nothing else this was a good learning experience. 

Careful with the discs. They are chemically coated and the coating is part of it's magic (seriously). If you have more issues creep in, get a new disc or diode

(the ohm balance was fine fyi. Sorry, limited net access so I shut off notifications except for @Adriatic  to draw me from hiding )

Nothing to be embarrassed about either; you found some knowledge that  had prevented progress that's all.    And now you get revel in the pride of success knowing the next issue will that much easier to tackle; Yey team!