Caution! New Russell Snow Plow shorted and burned

Sadly, that is not a new problem. It might be specific plow runs, but the fault I have seen is the filter capacitors were the wrong voltage location on the board.

In other words, there is a constant voltage board with a 7806 regulator. The high voltage input side must be a 35V rated cap (or higher) but the low side just needs to be higher than 6V. They got this wrong somewhere making the boards resulting the capacitor blowing and shorting, and that then cooks the bridge rectifier.

Again, have seen this first hand on these snowplows- looks like the same mistake was made more than once.

Edit- what I'm saying again is, I have seen more than one of the MTH and now ATLAS rebranded snowplows or Jordan spreaders, the new owner puts it on the track. In the past it might have been NOS or never run, just displayed, or maybe some miracle, run in conventional on such low voltage the cap never blew. You try it on 18V command track power and kaboom, smoke and heat.

Again, the circuit is a simple CV board, 2 capacitors, a rectifier, and 7806 regulator. But if the capacitor is in the wrong spot- bad things happen at track power.

Thanks @Jim M Sr for posting this and @Vernon Barry for adding details.

I have one of the TCA Strasburg plows.  I've run it in conventional mode, but not yet under DCS or TMCC.

Attached are pictures of the circuit board - taken from 3 sides so that the markings on the components are visible.  How can I tell if the right capacitors are in the right places?

Jim - how does this compare to the board in your plow?

Thanks.

I need a shot of the backside of the board, but I would consider caution.

The smaller capacitor is rated 16V, however, that is also closest to the bridge rectifier. Again, I don't have the circuit board in front of me and we need to see the backside to validate the path and wiring, but that looks suspect.

Edit- again, the working theory is track voltage, anything used in O scale and a rectifier at track voltage (~18V AC) I recommend a minimum capacitor rated voltage of 35V.

EDIT2- Also, given the known pinout of the regulator, the input side is left leg, common or DC GND is middle, and right left is regulated output.

Crude guess based on known pinouts of components but not seeing the traces

@Vernon Barry posted:

I need a shot of the backside of the board, but I would consider caution.

The smaller capacitor is rated 16V, however, that is also closest to the bridge rectifier. Again, I don't have the circuit board in front of me and we need to see the backside to validate the path and wiring, but that looks suspect.

Edit- again, the working theory is track voltage, anything used in O scale and a rectifier at track voltage (~18V AC) I recommend a minimum capacitor rated voltage of 35V.

EDIT2- Also, given the known pinout of the regulator, the input side is left leg, common or DC GND is middle, and right left is regulated output.

Crude guess based on known pinouts of components but not seeing the traces

Here's a shot of the underside, along with the board flipped over.

So, it's exactly what I suspected- a 16V rated capacitor, that needs to be 35V rated.

It will blow at 18V AC voltage input to the board.

@Vernon Barry posted:

So, it's exactly what I suspected- a 16V rated capacitor, that needs to be 35V rated.

It will blow at 18V AC voltage input to the board.

Thanks.

Since I don't have a 35v capacitor laying around, would it be feasible to swap in an AC/DC converter to provide the 6v output for the light?  (Putting a <$10 component in might be easier than contacting Atlas for a warranty repair or buying the part from MTH for $12 and adding $10 for shipping.)  Or maybe add a resistor to keep the voltage below 16v?

#1, based on what I have seen and am now seeing again, I think a whole bunch of these- including the boards at MTH parts- might have the wrong capacitor in that spot. Meaning- buying a new board and just plugging in may blow too.

Sure looks like a small cap is next to the rectifier

#2 Sure, you could replace the board and use a commercial regulator with AC rectifier- as long as it too has the required input rating. It's just 6V powering a couple of grain of wheat lamps.

#3 resistors are not voltage regulators. Sizing one to drop input power to this circuit is not a good idea and I know of scenarios where it will not prevent overvoltage to the cap making the effort just not even make sense.

I think, but do not know- the capacitors on the stock board may be able to be swapped- but note the polarity (white stripe on cap faces center of board) of each spot. I think maybe the larger diameter one may be higher voltage? None of the pictures showed me that (C3) capacitor label rating.

@Vernon Barry posted:

#1, based on what I have seen and am now seeing again, I think a whole bunch of these- including the boards at MTH parts- might have the wrong capacitor in that spot. Meaning- buying a new board and just plugging in may blow too.

Sure looks like a small cap is next to the rectifier

#2 Sure, you could replace the board and use a commercial regulator with AC rectifier- as long as it too has the required input rating. It's just 6V powering a couple of grain of wheat lamps.

#3 resistors are not voltage regulators. Sizing one to drop input power to this circuit is not a good idea and I know of scenarios where it will not prevent overvoltage to the cap making the effort just not even make sense.

I think, but do not know- the capacitors on the stock board may be able to be swapped- but note the polarity (white stripe on cap faces center of board) of each spot. I think maybe the larger diameter one may be higher voltage? None of the pictures showed me that (C3) capacitor label rating.

It's not clearly visible in my photos, but it looks like the larger capacitor says 16v on the side.

OK, reset, what is the rating of the small cap next to the rectifier? Zooming in from this direction I cannot be sure. Maybe 50V?  If 50V, then should be OK.

THanks for all the input.

I've not opened this one up to look inside as it arrived just yesterday and had less than 5 minutes track time. I'll let Atlas resolve it.

We were running DCS at 18 volts.

This is the second ond,most recent run that TCA just shipped out Friday.

The good, the bad, the unknown.

I dug into my spare parts pile and had on hand an example of the board in question from MTH parts. I bought 2 or 3 when doing the repair of a club members burned up snowplow and had recently bought my own snowplow and out of caution seeing one burned up bought a spare.

The bad- I can see I modified this board and it not as it came from MTH. Both original capacitors were replaced with capacitors I chose the values based on knowing the typical recommendations around 780X voltage regulators. As such, I used a 35V 330uF for the bulk, and then a 25V rated 22uF tiny capacitor on the regulated out (especially given the grain of wheat bulb load). Again, I am sure I modified this board and ditched the original factory capacitors- so I cannot be sure 100% what it originally shipped with.

What I can say is the picture below shows what bare minimum voltage rating i would recommend for both capacitors.

@Vernon Barry posted:

OK, reset, what is the rating of the small cap next to the rectifier? Zooming in from this direction I cannot be sure. Maybe 50V?  If 50V, then should be OK.

That one says 50v.  Is a sigh of relief in order?

@Mallard4468 posted:

That one says 50v.  Is a sigh of relief in order?

Yes. To me, the value is a bit low, most diagrams out there want a bulk capacitor roughly 470uF, and on the output, much smaller but at least from a voltage rating 50V on the input should not fail from overvoltage.

Again, what I know is, I have seen snowplows with the wrong voltage capacitor, and it was why they did or would blow up. Now what boards were built that way, is it random, a few batches, the reason why the OP's blew? I just don't know, but it's something worth checking IMO.

This is odd; pictures of circuits yet no picture of the snowplow! Is this an MTH or Lionel or Atlas?

FWIW: Last week I received my pre-order of Atlas Christmas Snowplow - non operating as far as I can tell...I am sure if it's original design or an MTH version.

@Paul Kallus posted:

This is odd; pictures of circuits yet no picture of the snowplow! Is this an MTH or Lionel or Atlas?

FWIW: Last week I received my pre-order of Atlas Christmas Snowplow - non operating as far as I can tell...I am sure if it's original design or an MTH version.

It's the original MTH tooling- now sold under the ATLAS name.

https://www.youtube.com/watch?v=pOdqrJ6E0y8

@Paul Kallus posted:

This is odd; pictures of circuits yet no picture of the snowplow! Is this an MTH or Lionel or Atlas?

FWIW: Last week I received my pre-order of Atlas Christmas Snowplow - non operating as far as I can tell...I am sure if it's original design or an MTH version.

Maybe some more background Paul.

https://ogrforum.com/topic/tca...g-snow-plow-by-atlas

@Paul Kallus posted:

This is odd; pictures of circuits yet no picture of the snowplow! Is this an MTH or Lionel or Atlas?

FWIW: Last week I received my pre-order of Atlas Christmas Snowplow - non operating as far as I can tell...I am sure if it's original design or an MTH version.

They don't "operate" - the circuit exists just to provide proper voltage to the LED headlight.

BTW, mine was very light and didn't track well when pushed - I added some automotive wheel weights.

Thanks Vernon and others. Now that I understand what this thread concerns, I'll share a picture of the model that I purchased - I found this Christmas snowplow= in a TrainWorld flyer, and pre-ordered it. By following Vernon's posts here, command control voltages could very well result in the circuit board burning up. Hopefully there will be more information as Atlas becomes aware of the problem. Until then, I'll box mine up with a sticky note about this situation.

@Paul Kallus posted:

Thanks Vernon and others. Now that I understand what this thread concerns, I'll share a picture of the model that I purchased - I found this Christmas snowplow= in a TrainWorld flyer, and pre-ordered it. By following Vernon's posts here, command control voltages could very well result in the circuit board burning up. Hopefully there will be more information as Atlas becomes aware of the problem. Until then, I'll box mine up with a sticky note about this situation.

Whether or not your copy has a problem might depend on when it was produced.  It sounds like the OP got one from the most recent run, while mine (which generated most of the discussion) is from the original run about a year ago. 

I emailed Stu Rankin, who handles the special runs for TCA, to notify him about this thread.  He's hoping that the OP's problem is a one-off.  I hope he's right, but considering the way the electronics are produced in batches, I'm not sure.

It's not difficult to remove the shell - 4 screws.  (I did it to add weight and I also stored the optional front coupler inside the shell so it won't get lost.)  Might be worthwhile to open it up and take a look at the voltage ratings on the capacitors.  With the shell off, you could power it up to 18v and observe what happens - if it starts to overheat, shut it down immediately.  If it doesn't get hot after a few minutes, it's probably OK.

Hope you got a good one.

Roger and thanks for additional information, Mallard. I just received mine about 2 weeks ago. My layout is in shall we say a state of cleanup and I hope to have operations resuming within 7 days.