tried installing old TCS T1 decoder in new locomotive, but function outputs don't appear to work.
I measure ~12V between the blue and white leads from the decoder which is for the front lamp. But changing the function (i.e. headlamp on/off or changing direction) doesn't seem to have any effect. Attaching a LED and 1k resistor drops the output voltage to ~6V and the LED still appears off.
I measure nothing (~0v) between the blue and yellow leads which is for the rear lamp. I believe CVs (49, 50) are set correctly for normal (0, 16) operation.
are these the symptoms of the outputs being "blown"?
thanks
greg - Philadelphia & Reading / Reading
Stuck 'on' is what usually happens when the function control transistor blows, because they are open collector current sinks. They yellow wire having no power, it might be off. If you reset the decoder it should revert any lighting CVs to the default plain directional headlight, in which case you should measure voltage between blue and yellow when the direction is set to reverse and F0 is on. It should be 0 volts if F0 is off or the direction is forward. White and blue should be the same thing, just in the opposite direction.
You shouldn;t be exceeding the diode voltage int he transistor with any sort of ordinary digital meter, but blue is the + side and the wires are each the - side. If you are measuring 12V between blue and white at all times, and you hook an LED with a 1K resistor in there, it should be on all the time. It would be rare for the failure mode to show full voltage in open circuit conditions (or at least, a high impedence multimeter) and not light an LED - with a 1K resistor that's like 9ma. I think you might have the LED backwards. But if there is voltage no matter what you do with F0, it's probably blown. CV30=2 should reset the TCS decoder, just to make sure the lighting CVs aren't all messed up.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
a reset fixed the function on the yellow lead. But the white lead is still the same.
Sounds like the white lead got blown and the yellow was configured to replace it - fine on an F unit with just a single headlight.