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Reply to "PS-2 locomotive only goes forward when horn button is held down?"

To be clear, I have not seen this either.  So I'm speculating. I'm suggesting the engine "thinks" it's in DC mode due to circuit damage.  I suppose it's worth a try to factory/feature reset the engine, but I suspect the engine will not respond to the Horn-Bell button sequences since pressing either button simply makes the engine move rather than triggering the respective sound.  But since it takes only a few seconds to try, why not.  So press the reset sequence and miracle of miracles if he all of a sudden get a double-horn-honk acknowledgement sound!

I think it is in DC mode because that's the only conventional mode where interruptions in track voltage do not change the F-N-R-N sequence. I think the engine needs to go to a tech.  My advice to said tech would be to look at the circuit that converts the AC track voltage to a low-voltage DC signal that is read by the processor chip using A/D conversion.  This is done with an op-amp.  It is via this circuit that the processor decides the conventional engine is in AC or DC mode when power is initially applied to the engine.  And then once in DC mode, it is this voltage that the processor chip averages to get the speed command.  Hence with regular AC on the track, the speed command is zero.  And when horn or bell is pressed, the average voltage is no longer zero so speed command is no longer zero with the direction taken from the polarity.  I believe there's something screwy going on in this circuit.

OP did not mention if he has DCS capability but it's possible that this engine would work fine in command mode!  The engine decides it is in DCS mode by looking for the watchdog signal via a different signal path than the track voltage measuring circuit.  Now that would be a new one!  Usually you hear about engines that work fine in conventional but not in DCS.

Last edited by stan2004

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