Akihabara Station

OSHI25-901 circuit board

This is the lightboard from the OSHI 25-901 dining car from the Tomix 92950 “Yumekukan” set. This board sits in a fitted pocket in the galley of the dining car. There are three SMD LEDs (the three white boxes on the left); three long lightpipes run from the LEDs to the rear of the car. The middle LED lights the taillights and signboard, and only lights when this car is at the end of the train—it doesn’t light when the car is at the head of the train. The outer two LEDs light two rows of table-lamps in the dining room of the car, and remain lit whichever direction the train is running. The two leads on the right connect directly to two steel strips that run along the bottom of the car and (in addition to providing much-needed ballast) contact pickups in the trucks. So, when +12V is fed across the leads (I don’t know which direction, to be honest), all three LEDs light; when -12V is provided, only the outer two LEDs light. In addition to the LEDs and resistors, there is what I’m guessing is an SMD bridge rectifier (for the table-lamps)? Although it has six pins instead of the usual four. And there’s some other tiny little resistor like thing by the middle LED.

The challenge before me: Convert this puppy to DCC. The board is too small to modify. And there’s no space to construct a replacement board. And, as many of my readers will know, controlling two independent lights with a DCC decoder requires three wires: Two “function” leads (that when activated, short to ground; when inactive they are left floating), and the +12V blue common. In my favor, there is a fair amount of room in the galley for additional circuitry, beyond just a decoder.

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