The Marklin sound cars are an easy way to add sound to your layout.
Most of the Marklin sound cars have a 21-pin decoder that is mounted upside down on the ceiling of the car. With rough treatment (for example during shipping), it is possible that the decoder can come loose. A quiet (soundless) car will be the result.
Luckily, it is very easy to re-seat the decoder. No tools are needed. The process is described in the picture tutorial below. We are using a new Marklin 43252, but the instruction can apply for other cars.