lionel LW 125 transformer help

[djrmmr]

The whistle button no longer works. The output is 19 plus volts but when the whistle button is pushed, instead of jumping to 25v as it should,the voltage decreases instead on the meter. I checked and cleaned the contacts on the whistle switch but nothing changed. Any ideas.???? Thanks.  All other outputs are good and operate as they should. 

[sir james I]

The rectifier disc is probably bad. You can get new replacements for them.

[cwburfle]

If the voltage is dropping, then the 6 volt compensating winding is not kicking in. I cannot recall running into a transformer with a bad compensation winding, so I guess that you either have a wire off, or a problem (bad contact) with the whistle control switch.

[djrmmr]

Now that I have the unit apart, I have found that the recifier disk has been removed and replaced with a very small square chip that had the red wire from transformer and white wire from whistle switch attached. I assume this is some sort of diode. I see there are two types of items available to replace the recifier disk on E bay. One looks like a small transister and the other which has a nut on it to secure to recifier mount. Which should I be using ?? Thanks

 

[cwburfle]

Without seeing the specific ads, there is really no way to tell for certain. The one with the nut is probably rated for considerably higher current, and would be the way to go. Generally the small ones are relatively low current.

Some folks recommend the following:

http://www.allelectronics.com/make-a-store/item/1n1190ar/40-amp-600-volt-rectifier/1.html

[lionelsoni]

If you install a modern silicon diode in place of the original copper-oxide, you should know that Lionel for some reason reversed the diode symbol on their postwar transformer schematics, including the LW.  So the cathode of the diode should connect to a switch terminal and the anode to a red wire from the 5.7-volt transformer winding and to one end of the resistor.  The cathode is often marked with a ring; or, for a stud-mount diode, there may be a diode symbol printed on the case.  Here is a link to the schematic diagram:  http://pictures.olsenstoy.com/searchcd31.htm?itm=658 

If you install the diode backwards, that is, in the way shown on the schematic, you will find that your whistle control has become a bell control for modern locomotives.  However, it will make no difference for postwar locomotives, which use a whistle relay.