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Dapol O Gauge Bubble Car Class 121/122

Dapol O Gauge Bubble Car Class 121/122

Kit: MX644C; YLR302815; 2x YC23R round speakers, LifeLink+17000uF SuperCap

Dapol's eagerly awaiting Bubble Car in O Gauge is here! Let's see what they've done and how best to put DCC Sound into...

The 21pin decoder socket is located underneath - remove 4 screws to access it.

A Zimo MX644C plugs straight in, and with our special project for this model, gives you immediate control to almost all of the lighting.

Initially we try a big YLR453520 speaker in the baggage area, but once the body is on, this becomes muffled and boomy - not a particularly nice effect, so we look at alternatives...

Dapol have provided space underneath for a pair of small round speakers which connect in series. Our YC23R 23mm 1W speakers work OK here and fit fairly easily, though not especially loud on their own. These provide good crisp top-end frequencies.

To complement these, a 2W YLR302815 8 ohm speaker can be added into the baggage area. Dapol conveniently provide a 2pin plug which you can join to the speaker, then this simply plugs into a socket that protrudes up into the baggage area. This connection is wired in parallel with the other 2 series speakers, so if you use 8 ohm speakers for all of them, you are within safe tollerances for the MX644 decoder. The overall effect is excellent - not mega loud, but loud enough, and very crisp.

Ok, great so far... but now we hit the issue with Dapol's lighting... firstly the leaflet that comes with the model has an error in that it lists the cab lights the wrong way around, but that is no big deal - we can just change the configuration to reflect that. More of an issue is that the interior lights are described as being connected to FA5 output of the decoder, but in fact there are multiple versions of the 21pin standard, and Dapol have picked the wrong one, and connected the wrong pin to this circuit!

As you can see from Zimo's documentation, FA5 is on Pin3 on an MX644, so this is the one that should be used.

We identify pin 3 in the model and attach a link wire as shown below...

Thankfully we can intercept the interior lighting quite easily on the model - you can see the black wire marked "IN-LIGHT", which we simply unsolder and join our link wire directly to instead.

All working nicely now.

The final job here is to add stay-alive. We use our LifeLink connection PCB with a 17000uF SuperCap, which fit neatly into the underframe box with the decoder.

In all it's glory, with all lighting working nicely. We tuned the motor frequency settings to get it running smoothly, by setting CV#112=32.


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.

A bit of YouChoos poster art for your enjoyment!