PhilP - Thanks for the document..........I'll review it to find the dimming CVs..........very difficult to understand. I had downloaded the LGB 55028 User Guide but didn't see anything about dimming of voltage for AUX 1 or AUX 2. And I had already looked at the Massoth 27 Pin sound decoder and it's totally different than the LGB/Marklin 55028 decoder. Interestingly, the LGB 55028 User Guide doesn't show any adjustment for sounds so I thought it was only a Driving/Function decoder. But the document you posted shows adjustments for sounds. And the LGB 20180 locomotive has a speaker I can see on the rear underside but I get no sound from the locomotive on the track........the original owner is deceased who installed the decoder into it. So, I'm wondering if the prior owner had actually installed the LGB 55029 MSD3 mfx/dcc/dc sound decoder instead of the 55028 decoder.
Okay, I opened up the locomotive and found the original owner had installed a Massoth XLS-1M DCC sound decoder, not the LGB 55028 Driving/Function Decoder. The XLS-1M seems to be defective, can't get any sound output. I connected another speaker to confirm it's not a defective speaker. So I'll try to update the decoder's firmware and reinstall a sound file using the Massoth Service Tool. I'll let you know if I am able to get the sound decoder to work or not. If not, I'll just reinstall the original analog board into the circuit board and post it for sale as a DC analog, no sound, locomotive.