MTH Crossing Signal With Bell Question- Bell Cuts Out **Update: Fixed**

It sounds like you're losing power to the sound unit; perhaps you are experiencing chatter or lighter cars at the back of the train.

You could try leaving the heavy engine at the point where the trigger device is engaged and see if the sound is maintained.

Also, you haven't told us what you're using as the trigger device. Please fill us in. Tell us about your wiring.

Bell and crossing flashers are powered separately from the track.

They are triggered by 2 pairs of Azatrax infra red detectors.

Locomotive or train position has no bearing on operation. I could trigger the crossing with my hand in front of the sensors and have the same issue.

The flashers never stop flashing. Only the sound will cut out at even intervals once it's has been activated continuously for 30 seconds or more.

That's why I wonder if there's a component of the speaker that is opening after voltage is on for extended periods for whatever reason.

I have wired it directly without sensors manually applying power and the same thing occurs.

Given the symptoms, I'd say you have a thermal issue.  After 20-30 sec of operation, something is heating up.  It fails, cools down for 2 sec and turns back on, warms up, fails again, cools down, lather-rinse-repeat.   After the train passes, the sound unit gets to cool down for a longer period of time as the train goes around the loop.  So on the next activation, it takes a bit longer to warm up to the failure temperature and then it starts acting up again.

It makes sense that lowering the voltage might make it operate longer since more heat is generated when higher voltage is applied.

Can you open the sound unit and post photos of the internal circuit board?  Given the price point of this item, I don't think it would be worth sending it in for repair...but perhaps there's a slim chance there's a user-replaceable component.  If it's a thermal cycling issue that occurs every 2 sec (very fast for a thermal issue), it would be a tiny component - hence hopefully inexpensive.

RickO: Thanks for the update. It looks like you've narrowed it down to the sound unit itself. As Stan said, it sounds like a heat issue. The circuit board should tell the story.

Most likely the sound is generated digitally from a memory chip that contains an MP3 recorded bell sound. It would not be a very long recording and would loop repeatedly. So the drop outs are most likely a failure either with power or with the sound amplifier part of the circuit.

I could not find anywhere among the MTH literature that they mention what voltage to use on this unit. I assume that they would want it to operate at track voltage (16 - 18 vac).

Try to get some really close pictures of the circuit board so that part numbers may be visible. A magnifier might be useful in that regard. An LED flashlight might help as well.

Thanks for the input Stan and Leo, Heres a pic of the Speaker control.

The 15 year old Panasonic Lumix Digital camera stil takes **** good photos LOL!

One lest test. I dropped the voltage  to 11.7, the bell stayed on. Maybe this crossing handles an absolute max of 12v?

The irony here is there is no voltage recommendation for this crossing by MTH anywhere

I saw the other thread on adjusting various voltages on an accessory bus. what type of diode would one need to add for just this speaker. I presume it would go in the hot wire to the speaker?

Well Stan, what do you think? I see 4 diodes in a close arrangement; has to be a bridge rectifier. Then a smoothing capacitor followed be a voltage regulator (laying flat with the heat sink) with another capacitor on the output side. That's got to be the AC to DC converter part.

What's left on this side of the board is a resistor or diode (under the connector) and Q1; the amplifier??? Doesn't seem like enough to do the job - does it?

It's a shame we can't see the other side of the board. It looks to be glued to the sides of the unit. Otherwise, nicely done Rick.

User serviceable? I don't think so. But there are still some things to try; like running it with the top off and checking the regulator for excessive heat.

Other than that, I don't know where you can go with this.

  -- Leo

 I just noticed.Theres one for sale on the " big auction site" It looks like theres one component that mine does not have by the R1 in the photo: https://www.ebay.com/itm/Mth-R...060778.c100290.m3507

Rick: I think I was typing while you were posting about the 12 volt solution. That would certainly make it run cooler. And if it's heat related, that makes sense too. I think you have figured it out!

If you want to use the diode method for voltage reduction, I know that Stan did a pretty good write-up about it in another topic. Let me see if I can find it; here it is:

https://ogrforum.com/...71#78438393724880771

Running with the cover off the regulator gets quite toasty.

Leo , did you have a chance to check out the photos in that link I provided. What is that extra tiny component mine does not have, is this why I'm having this issue?

Maybe there was an error at the factory when mine was produced, or possibly an upgrade after?

It figures, my warranty on these expired in January.

Rick: There you go again posting while I'm thinking.

Okay. Why would you buy a used sound unit in questionable condition when you've got one that works already? If you've got deep pockets and 35 dollars is worth the trouble, by all means buy it.

For $2.70 you could get a buck converter that would allow you to dial in the sweet spot for your unit. You'd hook your AC voltage to the converter, adjust the output voltage with a volt-meter, and hook it to the sound unit. I'm pretty sure that would work. Let me know what you think.

Consolidated Leo posted:

Rick: There you go again posting while I'm thinking.

Okay. Why would you buy a used sound unit in questionable condition when you've got one that works already? If you've got deep pockets and 35 dollars is worth the trouble, by all means buy it.

Understood, I was just curious if you had a chance to look at the photos at that ebay link and could tell if the component thats in the unit on the add, which mine lacks, is creating the problem.

I'd like to think a fair amount of folks have these crossing gates. I've never heard of anyone else complaining of the same issue.

I'm just wondering if the factory left off that "gizmo" by the R1 in that ebay photo and thats why mine is overheating.

The buck converter sounds perfect for my situation, easier IMO that trying to string in diodes. Everything else i have operates fine at 12-14v.  I justust need the buck converter for the speaker.

Rick: We are really playin' cat and mouse here.

I could not make out what was in the eBay photos; too dark for my old man diabetic vision. I did notice that the picture was the polar opposite of the one you posted. However, I doubt that you're missing any components. The thing works at 12 vac and that should be enough.

Fair enough, can you direct me to the appropriate buck converter?

Here's the number of a unit I bought recently:

323405457109

You know what to do.

Rick: Send me your mailing address and I'll send you one that I've got in reserve. There will be no money involved. We need to keep this moving along. Email should be in my profile.

From the eBay photo, I can just make out the marking on the regulator chip to be "L7805CV".  In other words, this gadget operates at 5V DC.  There is most assuredly an IC chip on the bottom/unseen side of the ring board with the "magic" audio chip that generates the bell sound.  And, yes, many of the inexpensive audio chips can use but a single transistor (perhaps Q1) to amplify the audio to the speaker albeit with low-fidelity (distortion) but suitable for this application.

Can you lower the AC voltage lower than 11.7?  I'd think it would work (with no reduction in volume) with as little as, say, 8V AC or so.   This would run even cooler.  Or if Leo is offering a "free" AC-to-DC converter that can be dialed in to any DC voltage that would also do the trick.

Finally got around to ordering that buck converter and wiring it to the speaker leads. It only took me a year

 I set the voltage just over 5.0 and viola!  The bell can ring and ring( i.e. if the train stops on the crossing) and no sound cutout, to the point I want to hit the speaker with a hammer LOL!

Fortunately I also wired an on/off switch to the speaker.

A belated thanks for all of the help Stan and Leo!