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.