Has your BLI loco lost its chuff?

At a recent operating session a friend asked me if I knew why his BLI Mikado had lost its chuff. All the other sounds were still there, just no chuff. After a little research on the internet I discovered that this is a fairly common problem with BLI steam locomotives. Instead of depending on the type of automatic synchronization schemes used in most other decoders, the BLI steamers use a magnet and reed switch detector method. A magnet is attached to the main driver and a reed switch installed on a circuit board directly above the magnet detects every time the driver makes a revolution. Inside the reed switch two metal electrodes close each time the magnet passes, and then they open again. The intermittent electrical contact they make is transmitted to the decoder which then uses that signal to synchronize the chuffs with the drivers’ rotation.

So what goes wrong and how do you fix it? Well, those little electrodes end up making a lot of movements and eventually they can stick together or even fail. When that happens the chuffs stop. Some folks say they have had success tapping the reed switch, but that usually only lasts a little while. Eventually you either have to send the locomotive back to BLI for replacement or order one from them and do it yourself. Although I have several BLI steamers I haven’t operated them long enough for this problem to arise but I do plan to order a couple reed switches from BLI for the day when the chuffs stop.

Replacing the reed switch involves removing the boiler upper half so you can get to the reed switch circuit board located over the drivers–here’s where that exploded diagram will come in handy. Then you have to unsolder the reed switch and install the new one in its place. This sounds like a simple enough procedure, once you get the boiler apart, and there are several posts on the MR website forum from folks who say it was fairly easy. The included photo shows the reed switch in a N&W steamer, it looks like a resistor in the center of the board. Good luck with it.


  • A minor correction if I may, Larry. The reed switch actually senses a magnet on the flywheel, not the driver. This probably adds to the premature failure of the switch as the drive shaft rotates maybe 14 revolutions, hence 14 on-off cycles, per driver revolution. I have replaced two of these already on my NYC Hudsons. So far, knock on wood ties, none of my other BLI steam has been affected.
    Good Luck, Ed

  • I have several older BLI steam locos and most have the original QSI decoders in them. QSI decoders (when the upgrade chip is installed) have the ability to electronically sync the chuff rather than use the reed switch . I have installed a LOT of different manufacturer’s steam decoders and the WORST is Soundtraxx / Tsunami. They almost require some type of cam to work properly. They have the “option” to electronically sync the chuff but it can only be done for a small speed setting. If you run slowly or faster, the sync is lost quickly. TCS is surprisingly stable as well as the QSI Titan and Revolution. I’ve installed axle cams as well. My most difficult install was a Westside PRR Q2 4-4-6-4. I used an 8-lobe cam from Grizzly Mountain Engineering http://www.g-m-e.com . I know this is old-school tech but it works perfectly every time.

  • I’m wondering how other sound decoder manufacturers synchronize the chuff to the drivers? If it is entirely through a digital process with no optical or mechanical sensor, I think BLI could be well advised to employ that same method. However, replacing the BLI decoder, especially that of the Paragon 3 with its “surround sound” capability, and incurring additional cost to the already somewhat high BLI price point just for an actual or anticipated failure of a simple reed switch does not seem, IMHO, practical. Why buy BLI in the first place? Other steam locomotive manufacturers have reliable engines and most if not all use Econami or TCS built decoders. Sure, there are exceptions to this generality and like me, maybe having all/only BLI powered equipment with Rolling Thunder is perhaps just a fetish. Just saying…

  • A recent issue my son had with his BLI Paragon2 Mikado is it stopped responding to throttle commands, on dcc it responds to sound commands but no movement. Works normally on DC. Any ideas what the problem is ? Tried cv8 reset. Probably will look at replacement with Ecour like David mentioned if there isn’t an easy solution.

  • Good to hear you had success with this David, is the smoke chuffs not operated by the same reed switch or are yours non-smoke?

    • Sorry Andrew I have been out of the country for the past 10 days. The ones that I converted were Paragon 2 non smokers.


  • I am disappointed that BLI uses a reed switch and magnet as the exciter for the chuff…this mechanical method is prone to failure. I would have hoped that BLI use a method less prone to failure, such as reflected light from a diode. I like the idea of changing the BLI decoder,; I never liked the chuff sound on their steam engines.

  • Larry I had this exact same thing happen to one of my BLI steamers and like you said I just ordered one of the reed switches from BLI. One note of caution is I would not attempt this if your solder skills are not very good or if you do not have an iron with a very small tip. One thing that I have started doing with my BLI steamers is to replace the Paragon Sound decoder with another decoder such as a Econami or TCS Wow. I have done both and when you do this you just eliminate hooking up the wire that runs to the reed switch and let the replacement decoder handle the chuff.