Intermountain F7 head lamp

[Mike Madonna]

Greetings all,

I was wondering if the head lamp in the IM F unit is a bulb or an LED? I presume a bulb, but it kind of looks like an LED.
Thanks in advance!

[sizemore]

LED

The S.

[Mike Madonna]

Thanks for the reply.

So to power this, I would need a resistor in the circuit? I know some drop in DCC boards have a resister in line.

[sizemore]

The IM F7 has its own board, just solder it back to the board. Are you missing the factory board? If you do a DCC conversion with a Digitrax board you just solder the LED wires to the DCC pads.

HTH,
The S.

[Mike Madonna]

Actually, I'm going to use the TCS IMF4 board. I want to add a "Mars" light to the upper head lamp and the lower will be the fixed "beam". The plan is to re-use the factory LED as the Mars light and a golden white surface mount LED as the lower. So F0, on the TCS board, will be for the SMT (this should have a resistor) and I'll have to use one of the other "pads" for the Mars. I'm just not sure if the other "pads" have resistors to support LEDs.

[peteski]

I'm just not sure if the other "pads" have resistors to support LEDs.

You can always add your own resistors.  I often do, like in this picture.

You don't have to get that fancy (etching your own printed circuit board). You can just either solder one end of the resistor to the decoder function pad, then the LED wire to the other end . Or install it inline with one of the LED wires (then cover it with heat shrink tubing or liquid masking tape.  If you handy in soldering, you can use SMD resistors. If not, get some 1/8W leaded resistors - they are quite small too.

[sizemore]

Actually, I'm going to use the TCS IMF4 board. I want to add a "Mars" light to the upper head lamp and the lower will be the fixed "beam". The plan is to re-use the factory LED as the Mars light and a golden white surface mount LED as the lower. So F0, on the TCS board, will be for the SMT (this should have a resistor) and I'll have to use one of the other "pads" for the Mars. I'm just not sure if the other "pads" have resistors to support LEDs.

You can always plop the board in the chassis, power it up and hit the right pads with a voltmeter. Most likely you'll need to solder in an resistor, you can get a $4!+ ton of SM resistors for super cheap, and take up less space than a coaxial lead resistor.

The S.

[peteski]

You can always plop the board in the chassis, power it up and hit the right pads with a voltmeter. Most likely you'll need to solder in an resistor, you can get a $4!+ ton of SM resistors for super cheap, and take up less space than a coaxial lead resistor.

The S.

Measuring a function output's voltage using digital voltmeter without a load on the output will not positively indicate whether there is a resistor in series with the output or not.  The meter's internal resistance is so high (usually 10 million ohms), that if there was a built-in series-resistor in the decoder, it will not drop any voltage (it will be negligible).

Best way to verify the presence of the resistor is to look at the decoder's specs (in the installation instruction sheet) or contact the manufacturer and ask them.  Or, if someone is handy tracing electronic circuit, follow the trace from the function output pad and see if it goes to a resistor (in the range of probably 400-2000 ohms).