Method to prevent sound dropout on Athearn FGE mechanical reefers?

[bbussey]

I have two of the sound-equipped Athearn FGE mechanical reefers, one as-built model and one of the modernized models in the Solid Cold scheme.  The sound unit works best when the model is stationary, because any disruption of power (dirty track, insulated gaps, etcetera) causes static loud through the speakers and/or causes the sound sequence to drop out and restart.  The sound unit runs on both DC and DCC.  I'm thinking a capacitor or a bridge-rectifier/capacitor combination integrated into the circuit, between the track pickup and the sound PCB may be a solution.  But wouldn't a bridge-rectifier already be integrated into the sound unit to handle the track polarity?  So the capacitor would have to be inserted into some part of the circuit on the PCB I'm guessing.  Any thoughts?  And what size capacitor would be enough to both smooth out the sound and handle the current?

[Iain]

DCC looks much like an AC signal, so a bridge rectifier and or capacitor between pickup and decoder would not work.  The decoder may have solder pads for adding a cap.  Otherwise, you might be able to trace out the circuit and figure out where one may need to go.

[peteski]

Are those sound generating devices DC-controlled decoders or are they just simple noise makers using track power?  If they are DCC decoders then they already have a bridge rectifier and some filter capacitors (as all decoders internally need a steady DC power.  The challenge now it to find the right spot in the circuit to add a larger capacitor.

If the sound generator is a simple "dumb" circuit, which works on DC and DCC, then those will also have rectifier and filter cap as that circuit also needs steady DC to operate.  Again, one has to find the right place to add the additional capacitor.

As for the size, we need to see what size is currently used and add a larger one. Probably something around 500 micro Farads.  But when adding a larger cap it might be prudent to add a resistor/diode combo (or a choke) in series with the cap to prevent large current spikes when the cap is charging. Especially when adding even larger capacitors (1000 or more micro Farads).

[bbussey]

I'll pop one of the cars apart and snap a photo of the board.  Maybe that will provide some insight.

[peteski]

I'll pop one of the cars apart and snap a photo of the board.  Maybe that will provide some insight.

Make sure it is a closeup of both sides.  BTW, what happened to the meatball project?

[bbussey]

Meatball?

[peteski]

Meatball?

Yeah, AEM-7 "meatball", "toaster". 

The Swedish influence led to the nickname "Meatball", after Swedish meatballs. Railfans nicknamed the boxy locomotives "toasters."

[bbussey]

Ah.  They're still on the table.  Currently waiting for new MTL coupler pockets from Shapeways.  I will revisit them at that point.

[Peter Amling]

Has anyone else experienced this problem or diagnosed it and come up with a solution?

[peteski]

Has anyone else experienced this problem or diagnosed it and come up with a solution?

The solution would be what I mentioned in the 3rd post in this thread. Since I don't own the car I can't really give any more specific into.

[jagged ben]

I can see why Brian may have never actually gotten a car open to get a photo.  The roof on these cars, which you would have remove to see the inside, is glued on.  It looks like it would be a pretty delicate operation to remove it and reinstall it with a proper fit and without damage to the paint.

The sound units are not DCC decoders, though.  A capacitor between the trucks and the sound board would probably work just fine.

[peteski]

The sound units are not DCC decoders, though.  A capacitor between the trucks and the sound board would probably work just fine.

Do you mean to hook up a large polarized (electrolytic or tantalum) cap between the left and right rail pickup?  Really?  That doesn't seem like a good explosion-free solution.    Bad advice, especially to modelers who aren't very familiar with electronics.
The cap really needs to be installed somewhere on the sound circuit board after the bridge rectifier.

[nscaler711]

I will have to take a much better photo... 

[ryan_wilkerson]

I'd like to cure this problem too. Thanks for getting into your reefer! How did you break into it?

I will have to take a much better photo... 

[peteski]

Taking an educated guess, looking at the blurry photos, the large silver cylinder marked 470 25V is the DC filter capacitor.  Adding more capacitors in parallel with that component would make the circuit more resistant to power dropouts. But I also assume that it is a surface-mount component so its leads are not easily accessible.

I would also not just add more capacitors without also adding a circuit which will limit the inrush current and also allow the additional capacitors to supply the energy quickly to the rest of the circuit (2 diodes and a resistor).