Heljan OO Class 35 Hymek (21pin version) with Zimo MS Sound

Kit: MS440C; SugarCube24X15X08; SuperCap17000uF

Heljan's 2022 re-tooled Hymek in OO has altered lighting to give independent control of headcode, tails and cab lights, as well as a 21pin DCC socket.

While the electronics are a welcome upgrade, there is no provision specifically for a speaker. A very low-profile one could probably go in the roof, but it would lack bass, so we have to look for another solution.

Our MS440C does the job for motor control and lighting, operating very smoothly.

A special version of our project for the MS440C is required to support the lighting, which is physically connected as follows:

• F0Fwd: front headcode
• F0Rev: rear headcode
• FA3: front reds (logic level)
• FA4: rear reds (logic level)
• FA5: front cab (logic level)
• FA6: rear cab (logic level)

Snapping off the battery box reveals a useful cavity, so just a question of working out the biggest speaker to fit, and how to route the wires up into the body.

The battery box pulls into 2 parts and a dual SugarCube24X15X08 seems to fit nicely cross-ways.

However, the question of how to get the wires up into the body is a challenge... there are slots where the rubber shoes for the motor fit, but we have to lift the whole motor out to expose these, which of course means that the drive shafts pop out!

We feed a pair of fresh purple wires for the speaker through, leaving plenty of length either end, and slide the motor back into position, easing the drive shafts back in as we go.

Heljan like to put 2pin sockets onto their PCBs for speaker connection, but have not included any 2pin plug to go into them, so we need to bypass this and solder the speaker wires direct to the decoder. The MS440 is not really designed to have this done, but with care we tin the appropriate feet up and offer the speaker wires to them. If you're not comfortable doing this yourself then ask YouChoos when you order the kit and we can solder the wires onto the decoder for you.

An alternative way to connect the speaker is to solder onto the rear-end of the speaker socket like this:

The blue and grey wires will be for the stay-alive - the MS440 often comes with these already attached (recently as stripey blue and black wires).

The decoder plugs in and we tidy up the wiring on top.

Underneath, we trim the speaker wires a little and solder them onto the dual SugarCube.

Unsure how well the sound will escape from the battery box, we create 5 holes.

A smidge of BlackTack and we can stick the speaker with metal face away from the chassis to avoid short-circuits. Tidy up the wiring and modify the battery box to allow it to slide back into place without pinching the speaker wires.

The final piece of kit is the 17000uF SuperCap, which is attached and wrapped in Kapton tape. This fits cross-ways right snug up behind the cab.

Please note that these guides are provided as useful resources for you, as-is. YouChoos cannot be held responsible for errors in the information, or for any damage caused to your models or equipment if you choose to follow any of the steps detailed here.