I purchased a Williams Digital Tru Blast II card last month to put into my Lionel MPC era GP7 Diesel (that did not have a horn). I was doing a temporary small setup under the Christmas tree. I installed it and it worked initially. Put in inside the engine chassis--it was tight, but got it in and wired it to convenient connections inside. I use Super O track and my transformer is a Lionel LW. I did notice however, that there was a particular way I needed to press the "whistle" button, though-- slow and deliberate but once I learned that I could activate it any time. Later, after dismantling that temporary setup, I moved the locomotive to my permanent layout in the basement, where I use a type KW transformer. That transformer's horn circuit works fine with my 2242 Diesel (which uses a horn relay), but I could not get it to work on the diesel with the Tru Blast II. All I would get is the first "note" of the sound. Tried varying my technique on the horn/whistle handle , but no luck. Hooked the LW transformer to the permanent layout temporarily and was able to get the horn to blow about half of the time. Reversed the terminals and the bell sounded, as expected.
I understand how the horn/whistle circuits work in the Lionel transformers (applying a 5 volt DC over the AC). Both of my transformers seem to be applying the DC as I am able to measure it with a voltmeter across the tracks set to DC. What I don't really understand is what is happening at the midpoint in the whistle switch activation. There is a point where the engine chatters, and then beyond that point, there is a "boost" in the AC track voltage. It is the first step at the midpoint that seems to be critical to to the horn sounding, or the sound card in the case of the Tru Blast II.
Anyone have any ideas what is going on here?
