I have a Lionel S-Gauge Berkshire number 1225 from the 6-49632 Polar Express FlyerChief RTR set purchased in 2016.  The smoke unit worked o.k. in the beginning, but now the smoke chuff feature does not work.  The smoke only comes out in a steady stream (very heavy I may add).  The chuff sound still works, but is not "connected" to the smoke output.  What do I need to look for to correct this?

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Well this isn't going to make you happy. I've recently worked on a number of failed Lionchief and Lionchief Plus based smoke units.  Verifying in the parts diagrams, your engine uses the same new "legacy" style smoke unit. Here's the issue, the smoke unit itself is not the fix. The problem is the tiny surface mount transistor that drives the fan and would chuff has failed into a constant on state. The problem is, that failed part is buried on the smoke daughter card of the Lionchief board, not on the cheaper and easier smoke unit itself.

Meaning, either you find a tech willing to take that apart, take the board stack apart, replace the transistor, assemble and solder the boards back together, and then put your engine back together or send it off to lionel, or buy if you can replacement pars and that part is not available. And it could be your fan motor ran dry on lube in the bearings, thus making it draw more current (I've actually heard one squealing brand new) and that's what could have blown the transistor.

https://www.lionelsupport.com/...a5-a7e7-7c570474a91c

Again, the fault is actually on the mainboard and is causing the fan to be constant on. The chuff also comes from the same mainboard, so it knows it's chuffing- but again the failure mode is either the transistor fails stuck on or fails off and never turns on. I've seen both.

691ENG9A01LIONCHIEF PCB / FLYERCHIEF POLAR BERK #122517$55.00 Unavailable

I just found an email I sent to a friend on these Lionchief "legacy" smoke unit repairs.

After examining your failed board with a magnifier, I saw the blown transistor that controls the fan. You can only see it with a magnifier, but there is a hole burned right in the middle of the chip blown out from the inside. It's marked "Y1" and double checked (since the marking was partially damaged when it burned) on the "B" unit good board.
 
Anyway, Y1 happens to be the same 8050 transistor Lionel and MTH uses in a ton of accessories- just surface mount size VS TO92 through hole size.
 
So next time- we know what the failure is. I think this happens on these Lionchief plus boards if the fan motor binds in the slightest, it draws more current and blown the transistor.
I have one in the kit I got from amazon.
 
 
gunrunnerjohn posted:

I suspect that "transistor" is probably a FET.

No, sadly not, these LC and LC+ boards still use a lot of BJT. You aren't wrong in your thinking though, a transistor that fails on is most likely a MOSFET, but that's not what they used.

Y1 happens to be the same 8050 transistor Lionel and MTH uses in a ton of accessories- just surface mount size VS TO92 through hole size.

Well, they should have been a FET, that would handle several hundred milliamps, likely more than the on-board DC regulator could supply.   I use a FET to drive the smoke motor for my Super-Chuffer, it is a SOT23 SMT package and handles 1.2A continuous.  Considering they're no more expensive than a transistor, that would be my choice!

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