Railsounds Board 5.5 No Sound

@Steims posted:

I found that there was an open in the wires to the speaker.

Would that cause a subcomponent to fail on the Railsounds 5.5 board? Yes, absolutely an intermittent connection or worse, that potentially opens the door up for a short to frame ground or something else could and might blow the audio amplifier IC.

The removable chips work when I swap them to a known working board.   Good, you got lucky. That's about as lucky as you can expect. A typical fault it kills the chips and then you are soundless.

FWIW recent failure on a Lionchief of the audio amp- using a microscope LCD camera. You might not see this damage with the naked eye at first.

A 3.3V regulator exploded when the short in the audio amp was backfeeding AC up the DC low voltage circuit.

The pinched speaker wire only had an open and no short to ground.  That would cause the sound board to fail?    Seems like Lionel built their  electronics more robust than that to handle various failures and faults.  

The pinched speaker wire was doubtless shorted when it was pinched I suspect.  An open to the speaker shouldn't kill the RS board, I've seen many of those.  OTOH, shorting a speaker lead to the frame will kill them.

@Steims posted:

The pinched speaker wire only had an open and no short to ground.  That would cause the sound board to fail?    Seems like Lionel built their  electronics more robust than that to handle various failures and faults.  

I must ask the simple questions first. Did it how sound at one point? Everything else work fine in command as well as Conventional operations?

little advice, there are times a chip is defective from production and will show no outward signs. What ever board you are swapping too remember that of internal the “problem” could blow the test board.

the speaker wire was probably shorted and took the board with it, when you moved things to test you opened the short.

@ThatGuy posted:

little advice, there are times a chip is defective from production and will show no outward signs. What ever board you are swapping too remember that of internal the “problem” could blow the test board.

This is my TMCC test fixture, it's grown over the years.  I can test most aspects of TMCC and early Legacy modular boards on this one.

@gunrunnerjohn posted:

This is my TMCC test fixture, it's grown over the years.  I can test most aspects of TMCC and early Legacy modular boards on this one.

I made my test bead from an old radio shack radio kit. I used the clip on part of the board and then went with e every thing else needed to test the boards. The one difference I see with your DC motor mount and mine is I can simulate a load with a drive wheel and slip clutch. I have seen boards that need to heat up to stop working.

I appreciate the advice especially since these boards are no longer available from Lionel.  I bought loco used and had no sound when it arrived.  I could tell some troubleshooting had already taken place.  

My takeaway from this is to make sure the speaker wire circuit has no open, has no short, and is not grounded to frame, before I power up a replacement sound board.  

@ThatGuy posted:

The one difference I see with your DC motor mount and mine is I can simulate a load with a drive wheel and slip clutch. I have seen boards that need to heat up to stop working.

I have a left hand that holds the flywheel if I need a quick load.  If I need a more sustained load, a power resistor across the motor does the job just fine.   This has been added to over the years as more situations for testing come up.  It started as a simple board tester.  If I knew it was going to grow like this, I'd have planned the layout better.

Sounds (ha sorry) like you killed the LM4861 audio driver. Lionel uses these in a bunch of their audio boards from my research. I think it drives the speaker directly, at least the tech sheet supports that. Perhaps the audio board might be salvageable if you replaced the driver.

@gunrunnerjohn posted:

I have a left hand that holds the flywheel if I need a quick load.  If I need a more sustained load, a power resistor across the motor does the job just fine.   This has been added to over the years as more situations for testing come up.  It started as a simple board tester.  If I knew it was going to grow like this, I'd have planned the layout better.

If I knew what I know now……….we’ll you know…..LMAO

@Norm Charbonneau posted:

Sounds (ha sorry) like you killed the LM4861 audio driver. Lionel uses these in a bunch of their audio boards from my research. I think it drives the speaker directly, at least the tech sheet supports that. Perhaps the audio board might be salvageable if you replaced the driver.

I’ll give it try Norm as long as somebody can point to which discrete component that is on the board.  

See the tech sheet attached.

There is an audio amplifier on both sides of the board.   One has an ever so slight blister on it so I think we are onto something here.   Digi-key has 2 models of this as LM4861M and LM4861MX, which one?

Maybe one superseded the other? I wasn't aware there were two amps on the audio board. I wonder if there's a block diagram of those boards somewhere in the world. The pinouts are fairly easy to find with a Google search but I've never seen the block diagram. It's still a real shame Lionel took those TMCC boards off the support site.

Edit: the other 8 pin SOIC might be an LM358 op amp.

Looks like one amplifier for each sound chip, maybe?  I don’t have the board in front of me but I will closely check the markings when I get home to see which model of LM4861 was used and if in fact they are both actually amplifiers.

@ThatGuy posted:

I made my test bead from an old radio shack radio kit. I used the clip on part of the board and then went with e every thing else needed to test the boards. The one difference I see with your DC motor mount and mine is I can simulate a load with a drive wheel and slip clutch. I have seen boards that need to heat up to stop working.

Not to hijack Steim’s thread, ….but let’s see your test fixture!!….

Pat

@harmonyards posted:

Not to hijack Steim’s thread, ….but let’s see your test fixture!!….

@harmonyards posted:

Not to hijack Steim’s thread, ….but let’s see your test fixture!!….

Pat

No, not relevant to the post.

@ThatGuy posted:

No, not relevant to the post.

Uh huh,….gotcha ….

Pat

@harmonyards posted:

Uh huh,….gotcha ….

Pat

You got thing, but nice try…….lmao

@Steims posted:

There is an audio amplifier on both sides of the board.   One has an ever so slight blister on it so I think we are onto something here.   Digi-key has 2 models of this as LM4861M and LM4861MX, which one?

The two chips are the same, it's a packaging designation.

@Steims posted:

There is an audio amplifier on both sides of the board.

Sometimes those are used for power handling chores, could it be one it a non-audio use?

@Norm Charbonneau posted:

…the other 8 pin SOIC might be an LM358 op amp.

Norm, you were exactly right.  On the back of the board is the LM358 op amp.   The front has the LM4861 amplifier.   My amplifier has a blister on it.   I also found that large diameter C12 capacitor (220 uF) has an open.  

A capacitor will read open with an ohmmeter after it charges.

I tested all 4 caps on this Railsounds 5.5 board as well as another.  Seven of the 8 caps uF readings were in the ballpark of their listed rating.   The one with open stood out from all the rest.   The comparable cap on the other board read 232 uF.  I am using a digital Fluke with a cap testing function.  

I've seen those 'Boomer' amps on the RS4 and RS5 boards, also on some of the ERR and Legacy sound boards. Without a block diagram, I couldn't say what the 358 op amp is for. I like to gawk at the boards once in a while and look up the components to get a rough idea on what does what. I still can't get over how overbuilt the old RS4/5 power supplies were. I can only guess that their audio engineers wanted zero sag when driving the sound. Whatever they did back they did well because those are still my favorite sounds.

I got one of those ESR meters for testing caps. I'm becoming a fan of all the cheap ebay/Amazon test equipment. You have to outsmart them a bit, but they are kind of fun to play with.

@Steims posted:

I tested all 4 caps on this Railsounds 5.5 board as well as another.  Seven of the 8 caps uF readings were in the ballpark of their listed rating.   The one with open stood out from all the rest.   The comparable cap on the other board read 232 uF.  I am using a digital Fluke with a cap testing function.  

Testing caps in circuit is a bit of a crap shoot, depending on what is connected, you can get all sorts of odd readings.  If the same cap on another board tested OK, then it makes sense.  It's pretty rare for a cap to be completely open without any physical appearance issues.

I didn’t see any physical distress on that cap so I will take some more readings on it before I pursue replacement.  
As for the audio amplifier, I’ve ordered a fine tip for my solder iron and I got some jeweler’s lighted magnifying glasses.   Any other tips to be successful in such a small, small world?

Well, when I remove those, I clip each lead, remove the body, then sweep the leads away with the iron, much less issue of PCB damage that way.  If you have a hot air tool, you might be able to lift the old one, but why bother?

The LM486 being a SO package isn't that difficult to solder, you just need a fine tip.  You will want to clean up the pads before installing the new chip.

As always, I appreciate the advice GunrunnerJohn and others.  Worst case it doesn’t fix the board but it wasn’t working to begin with.