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I had an odd one on the bench, something that I didn't realize was possible.

I have an MTH Imperial FEF for repair.  Once I got everything working in command mode, I tested it in conventional mode.  I cracked the throttle so it got 6-7 volts and it powered up.  After it sat for 30 seconds or so, I cycled direction and I got the startup hissing chuffs and corresponding chuffing smoke.  Then the standard chuff sound started, again with the chuffing smoke.

WAIT!!!

The wheels aren't turning!  I kid you not, no wheels!

OK I think, the driveshaft has come loose and just the flywheel is rotating, off comes the shell.

I do the same test again, same result, only the flywheel isn't moving at all!  I was pretty surprised, I had no idea the electronics would generate the sounds without the tach sending feedback!  It was just like the locomotives was rolling down the tracks, chuff sounds, smoke chuffing away, and no motion!

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I had an odd one on the bench, something that I didn't realize was possible.

I have an MTH Imperial FEF for repair.  Once I got everything working in command mode, I tested it in conventional mode.  I cracked the throttle so it got 6-7 volts and it powered up.  After it sat for 30 seconds or so, I cycled direction and I got the startup hissing chuffs and corresponding chuffing smoke.  Then the standard chuff sound started, again with the chuffing smoke.

WAIT!!!

The wheels aren't turning!  I kid you not, no wheels!

OK I think, the driveshaft has come loose and just the flywheel is rotating, off comes the shell.

I do the same test again, same result, only the flywheel isn't moving at all!  I was pretty surprised, I had no idea the electronics would generate the sounds without the tach sending feedback!  It was just like the locomotives was rolling down the tracks, chuff sounds, smoke chuffing away, and no motion!

                   ?    🙃

I am all command mode with Premier so you got me.

I can only guess the sound is controlled by voltage in conventional. Maybe the tach is for constant speed control only?

Does rail king with loco sounds have a tach and reader? or is it a magnetic reader on an axle like lionel?

but even that wouldn’t make sense if it wasn’t moving.

Did you rule out the chuffing-in-idle scenario (the one solved with a tach resistor)?

I suppose you would have said if you put the scope on the tach signal but to your point in the other thread perhaps something is modulating/pulsing the 5V power supply which ripples into false tach pulses.  If the PS board has a direction-relay I believe those are powered from 5V and you mentioned this started when you "cycled direction" which I assumed meant you put it in reverse.  Likewise I believe the smoke fan motor PWM is sourced from 5V - so for example if you turn OFF the smoke did the audio still chuff with no motion?

So we're talking the PS3 boiler board.  Got it.  But could it be the same issue?  Could some load intermittently modulate/drag-down the DC voltage that powers the tach LED/sensor in the boiler.  That can introduce false tach pulses.

Hence, for example, if 5V is used for the tach and boiler fan motor PWM, what happens if you turn OFF the smoke?  Separately, if we're talking about PS3, I believe the LEDs are PWM'd from 5V DC.  Again, if this is the same 5V DC that powers the tach optosensor, does the false chuffing go away or change if you turn off any/all LEDs in the boiler?

Last edited by stan2004

It did it with smoke on or off, but only if the track voltage was too low for it to get going.  I just found it odd that it was regular chuffs, just like it was moving.

I realize you've already put this to bed.  But for the record in case this comes up again, when you say "too low to get going" does this mean the engine is in conventional FWD or REV (not neutral) and the motor is being driven...just without enough voltage so it's stalled?

Stated differently, if the engine was in neutral, did you every get the false chuffing/puffing?  And if so, did false chuffing disappear when raising track voltage (engine still stopped because in conventional neutral).

Trying to isolate if this is something that "only" happens when the motor is actively pulsed (albeit in vain) at low track voltage.

The motor was being driven, but it didn't have enough power to actually start moving.  It wasn't in neutral.  In neutral it behaved as it should.  This happened in forward or reverse.  Obviously, increasing the throttle enough to start the wheels moving returned it to normal chuffing.  In another odd twist, reducing the throttle again in forward or reverse so the wheels stalled, the chuffing didn't continue.  It was only from a power up that I was able to get the "false" chuffing.  The engine is on it's way back to the customer, so that testing is over.

....  The engine is on it's way back to the customer, so that testing is over.

Yup, I figured the train has left the station.

I suspect this may never come up again.  And, if this was a systemic issue with PS3 boiler electronics, I'd think it would have been observed and reported albeit conventional PS3 operators aren't in the majority.

But if this comes up again by anyone, please tack on to this thread so I'll get a notification.  This is one of those curious cases that would be interesting to solve just for the sport. 

6-7 volts seems pretty low for PS-2 or 3 boards and winds up drawing a higher current flow.  Plus you intentionally had the motor in a stall condition at that voltage.  I always power up to 10V and then up to 12 once started up.  It was always brown out that damaged sensitive electronics in my prior life.  Not clean breaks in power.  So I am leery of trying to run electronics at a marginal voltage.  G

According to Jason and the service bulletins, as long as you use the proper chain files, you can mix-n-match EMI and non-EMI boards.  I know I just loaded a PS/3 board set with the relay board (non-EMI) with an EMI tender board, runs fine.

This is the service bulletin that addresses that issue: service_bulletin_101017a

If you don't have the correct code, you can run into issues.  I had this happen one time early on, the boiler board obviously was fighting itself and apparently turned on all the motor driver FETs at once.  Fortunately, I had my bench magnetic circuit breaker enabled, and the breaker tripped immediately and didn't cook the board.

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