Kit: MX649 (hard-wired); SugarCube speaker component; SACC16 with 2x 330uF Tantalums
Lovely little model of the J70 tram engine, nice and weighty and well designed electrically.
The 6pin DCC socket is a little tight to the PCB though, so an MX649N direct plug-in sound decoder is rather awkward to
reliably plug in, even with bending the pins to step-shape.
So we take the decision to remove the 6pin DCC socket, and hard-wire the decoder directly. Our first attempt involves soldering
the pins of an MX649N directly to the remainder of where the 6pin socket was, but this proves rather tricky, and isn't an
approach we'd suggest for most people.
Therefore we swap to a wired MX649 and solder short wires direct to the motor points and the pickups, which is actually quite
easy on this model - a much better approach!
Some thin double-sided sticky tape to hold the decoder loosely in place, and the decoder re-covered in Kapton tape, sits nicely
on top of the factory PCB now.
Motor and pickup wires are easily accesible, so solder those up. We have removed any AUX wires, as we won't be adding any
lighting to our model.
The only wires are for the speaker, which are at the other end of the decoder.
The model comes pre-fitted with a speaker in a custom enclosure, which is very nice - we could just use that, as it appears to
be an 8ohm speaker anyway, but instead we just swap the speakear component for a SugarCube component, and glue this onto the
enclosure. Solder the purple speaker wires on, ensuring that they don't touch the metal parts (is quite close!).
***** BEWARE ***** some J70 models have found to have been factory-fitted with duff speakers, measuring less than 1 ohm rather
than 8 ohm - always measure the impedence of the speaker before connecting up, or simply swap for a known 8ohm component!
It is a good model, but it is small, so a little bit of stay-alive will always be useful. We connect in a SACC16 with 2x 330uF
flat Tantalum capacitors, cover with Kapton, connect to the decoder's common positive and ground pads. This sits on top of the
decoder - there is just enough vertical space here, so is quite easy, and makes all the difference to running quality.
The finished article...