Intermountain F7 Next18 PC board mapped out

[peteski]

There was a question about finding the ground (negative) connection for adding a keep-alive module to this model so I decided to document this board's design.

This board (actually designed by ESU) does not have either the U+ or GND pads for easy connection for a keep-alive. Why don't manufacturers include those connections when more and more modelers want to add keep-alives to their models?

That was the bad news. The good news is that unlike the recent Atlas E24 light boards, where no GND signal is available at all, this board has both, GND and U+ accessible.


IM_F7_PCboard.png

The GND signal is accessible pretty much everywhere on both sides of the PC board because ESU  (like they do on their decoder PC boards) included large ground plane copper areas.  They are covered with a solder mask layer, but carefully scraping that hard black coating will expose bare copper to access the GND.  I highlighted the major GND areas on the top of the board because that's likely where GND will be accessed, but GND is also accessible on the bottom of the PC board.

It is U+ that is a bit more difficult to connect to.  As the above image shows, the U+ is accessible at both connectors, at a short trace close to the Next18 connector, or on the U+ trace on the bottom of the PC board highlighted in red.


IM_F7_PCboardSchematic.png

For those who are curious, here's the schematic diagram of the board.  Since on the ESU's Next18 connector the AUX3 and AUX4 are only available as logic-level outputs, they included couple of "amplifiers" (consisting of a transistor, resistor, and a cap) to convert logic-level to power AUX outputs for driving the number board and the Mars light LEDs.

The switches have me a bit puzzled.  It appears that if the model only has a single (upper) headlight then the headlight AUX output is routed to it. If the model has dual headlight setup, the Mars light AUX is routed to the upper headlight housing, while the lower housing becomes the headlight.  Seems to me that instead of physical selector switches all this could have been done within road name-specific sound project's function mapping  uploaded to the decoder where the Mars or headlight function would be mapped to the specific AUX output.  Maybe IM did not want to end up with several different sound projects for this model.

[jwaldo]

I suspect the on-board switches for changing light configuration make it easier to put any shell on any mechanism at the factory. But as a customer who's not afraid to buy whatever road name is on sale and modify/repaint it to SP spec, I can certainly appreciate it.

[peteski]

I suspect the on-board switches for changing light configuration make it easier to put any shell on any mechanism at the factory. But as a customer who's not afraid to buy whatever road name is on sale and modify/repaint it to SP spec, I can certainly appreciate it.

Well, you're probably correct, but this could have been just as easily accomplished  by mapping the appropriate AUX functions to specific headligth or headlight/Mars combination (either at the factory, or by the modeler).

AUX4 (Mars) could have been hardwired to the upper housing and Headlight AUX to the lower housing.  Then in the function map the AUX4 and the Headlight AUX could be easily mapped on the decoder to either effect.