Bad-ish LM-2S?

[CPRail]

Happy Holidays Gang,

I decided to complete a long lingering install today using a LM-2S that I purchased used. I bought a pair of them and the sibling has been happy happy, so I was expecting no issues.

The install is in an old Athearn Blue Box SD40-2. I did the initial hookup and while trying to do a motor load test, realized that the Athearn motor has seen better days. The LM was getting warm and I couldn't get it the test to complete twice without getting an Overload message.

Thankfully, I have a pair of old Proto Power West SD45 re-powered chassis' sitting around, so I re-motored our candidate with one of the Mashima can motors PPW was known for. That solved the motor issues!

I'm using an Athearn DCC Quick Plug board, with wires to the trucks, one soldered on the big truck tab, and one soldered to the opposite side ala current Athearn/Genesis wiring. I also have a bridge rectifier soldered in on the red & black wires with a KA-4 connected in. Cumbersome, but it is a LM-2S so needed.

Hooked up everything again and started some test runs. Got a nice low motor test, so started tweaking the various settings. After running it back and forth, I started smelling the distinctive smell of unhappy electronics. The LM-2S was also feeling warm. Uh oh...

I have a bunch of LM-3S modules waiting on other installs, so I unplugged the LM-2S and plugged in a LM-3S. Everything went back to happy happy, with no smell.

Odd thing is the Info page on the HC did not say anything of overheating etc. Temp was in the middle of the range.

The LM-2S worked fine, but the unhappy electronic smell without the shell on has me worried. Is my LM-2S buggered? How do I tell?

I don't want my railroad to be renamed the Chernobyl Central. We've already experienced one of those here - a large layout running Dynatrol (remember that?) that had some spectacular meltdowns back in the day!!

Thoughts?

[G8B4Life]

How warm is warm? Unpleasant to touch? I'd expect the LM to get a little warm under load but not so warm it felt hot to touch.

Depending on the smell it could be some component giving up the ghost or possibly (very long shot), depending on what it is, the residue burning off. I have seen some sort of residue of the top of some components of the LM board. It could be some residue from the soldering process or some goop that's deposited deliberately as part of the manufacturing process. I don't know which it is so that's why it's a long shot.

To look for damage there's really only two things to do. First feel the outer casing for deformities and then, if you dare, opening the casing up and looking for damage to the components. You need a good magnifier for that. As the LM is second hand I suspect Ring repairing it won't be an option so you might have nothing to loose by opening it up and checking the board out.

- Tim

[William Brillinger]

I'm sure ring would repair it for a small fee.

[CPRail]

Here's the latest and greatest:

I put the loco on the track with the RP system on and immediately starting smelling the unhappy electronics smell with some mild heat. No movement, just sitting there with track power on.

Updated the LM-2S to the current standard and uploaded a sound (horn) and assigned it. Could not get the horn to play.

Plugged in a known LM-3S and got the sound to play and loco to move. Notably the sound was quieter than last night using the same module and speaker - this should've been my first warning.

Reinstalled the LM-2S but without speaker for a moment. Nothing smelly, no heat. Plugged in the speaker and within 15-30 seconds the unhappy electronics smell appeared and the module starting getting warm. Waited a moment (45 secs ?) and the module was warmer, to the point where if you held your fingers on the narrow sides for about 15-20 secs you'd start to think about removing them.

Checked the bridge rectifier - it was getting warm as well.

Inadvertently touched the speaker driver and damn near burned my finger!!

This explains the speaker having less volume and the static-y sounding speaker I originally installed. We are getting some serious power leakage through the speaker.

Too bad I killed two $18 speakers to find this out.

I wired in the bridge rectifier like I've always done between the red & black wires on the harness, with the KA-4 on the module side. I double-checked that I had the BR the right way round as I screwed that up once - all good.

So, electrical gurus, where's the problem?

[William Brillinger]

"So, electrical gurus, where's the problem?"

Open the LM and look it over.

[G8B4Life]

I'm not sure of how you could test this, I'm no electronics guru but from the sounds of it one or both (there is two on the board I believe) of the audio amplifier IC's is damaged (shorted open, you should not get any power out to the speakers unless you press a button). No heat and smell when nothing is connected to the speaker connections supports this. As you noted the speakers are probably damaged now as well and I wouldn't use them until you can confirm their impedance is still good.

The rest of the LM may be fine as you can connect to it and update it etc or are there other issues besides what's going on with the audio side fault?

- Tim

[Alan]

Speaker voice coil is shorted.

[CPRail]

The LM works fine, just no noise and cooking speakers. As Alan mentioned, it's shorting across the speaker voice coil.

I need a module to drive my turntable motor. No sound needed there. Can I use this LM for this application?

[Alan]

The LM works fine, just no noise and cooking speakers. As Alan mentioned, it's shorting across the speaker voice coil.

I need a module to drive my turntable motor. No sound needed there. Can I use this LM for this application?

As long as your turntable motor draws less current than the drive output of a LM, then sure. Assuming your turntable rotates reasonably free then I doubt its motor will exceed LM capability.

[G8B4Life]

I need a module to drive my turntable motor. No sound needed there. Can I use this LM for this application?

Yep, sure can. Just load the accessory program to it and then you can download the turntable project to it (project may need to be modified a little).

Backing up a little, You noted that you've damaged two speakers now. Were they both wired up to the LM at the same time? I'm wondering if the audio amplifiers on the LM were damaged when you got it causing it to damage the speakers or if the speakers you used were to blame (ie, they were only 4 ohm and if you wired them both in (in parallel) you only got 2 ohm load) which damaged the LM.

Edit: Alan got in before I did and makes a good point on the current draw of the turntable motor. If the turntable motor draws more current than the LM can handle you can always use the LM to drive something like a power transistor so the transistor supplies the power to the turntable. How you get the motor to go forwards and reverse in this case is not something I can think of at this time of night (I need to sleep on it), our old transistor DC throttles used to use a toggle switch after the transistor for that part but that's not what you want in this case.

- Tim

[CPRail]

Speakers were single, no double hook up. I use Scale Sound System speakers - they are rated at 1W, 8 ohm.

[KPack]

On the dozens of modules I've installed, I had a single one with a bad amp.  It was working fine, then out of the blue the sound spiked and cut out.  Motor movement ceased.  When powered, the module got extremely hot right next to the 6 pin plug (LM-2S) where the amp is located.  Sent it into Ring and it appears that a small piece of stray solder from assembly had come loose and shorted the amp.  The module was replaced.

Your situation sounds similar to what I had, minus the blown speakers.  My speakers were fine.  Shoot Ring an email or call them and see what they suggest.

-Kevin

[Alan]

May want to check if the speakers are really "blown". It may be a case of them getting hot because the LM was feeding them DC. The LM doesn't have enough wattage to blow them in the conventional way - over extension of the coil. They may be okay.

[CPRail]

Good to know. Thanks Alan.

They sure smell bad, even unplugged, but I'll give them a test.

[CPRail]

Continuing the saga, I just checked the speaker leads on the suspect LM-2S– it’s putting out 4.8V. A new LM-3S that I also tested is putting out 0.12V for the speaker. Something is definitely fishy in Camp Wiganishee!!

Also, the LM-2S is still getting warm, even without the speaker plug.

Open it or send it to Ring?

Oh yeah, Happy New Year!!