Upgrade audio amp

It can and it is a possibility.  Normally a shorted speaker would cause issue.  If is possible the speaker shorted before failing open.

I can replace the audio amp.  I would not run it unless you can monitor amperage.  Shorted audio amp can overload other portions of the board if allowed to be powered up.

I would only need the board set, not whole engine.  E-mails is in my profile.  G

It seems like the audio amp on the 3V boards is their Achilles Heel, I had several in just a couple of months!  The good thing is that you can replace them, but I wonder why they're so sensitive?

I believe I may have found the culprit.  I examined the damaged speaker and found one of the wires that connect to the coil to be very close to the frame.  Using my voltmeter I was able to get continuity to ground when I flexed the speaker cone.  I also looked at the replacement speaker (also from an upgrade kit) and saw that the wires were longer than usual and also very close to the frame.  A little adjustment and they are fixed.

While I will never be certain this was the true cause, it does fit the clue (burned out speaker that had been working fine).

That's very keen troubleshooting on your part!  While that amplifier chip and virtually all like it have built-in protection against shorted speakers and even shorts to the amplifier's low-voltage power supply, a short to the chassis/frame exposes the amplifier output circuit to track voltage.  That chip uses FET (transistor) drivers at its speaker output very similar to the discrete FET drivers for each light and smoke output.  And we know that inadvertently shorting one of those output wires to the chassis will pop that FET requiring replacement.

That was a sharp eye Scott, nice catch.

I told Scott to look for that.  It is a know cause.  Some early post are available on this subject.  I usually move the wire and then use liquid insulation on those wires to ensure no shorts when routing is too close.  Something I check and do for any speaker replacement and or upgrade.

Stan, I don't think the protection of the TI unit used on PS-2 3V works very well.  Fan motor issues, Track spikes/derailments, speaker issues, all seem to blow the audio amp quickly.  5 or 6 out 10 times the speed control amp goes with it.  G

George, where is the speed control amp?  Is that another part that can be replaced?

Component U12 on the power board and it's a 8 legged chip..fairly easy to change.

What Chuck says.  They are the 2 components MTH stocks besides the small FETS for lights, smoke, etc...

Other items are listed, but MTH doesn't stock the parts for resale.  G

Is there a part number for this part, say on Mouser or Digikey?

LMV358M.  84 cents at Digikey.

A big thanks does go to George for pointing this out to me.  I am happy to have found an assignable cause out of a list of possibilities.  When doing upgrades, I have always checked for shorts against the speaker frame but never thought of the wire hitting the frame when the speaker was in use.  Examining a new speaker with the same problem really made this hit home.  My next step is to examine the speakers from my other upgrades & look for the "ticking time bombs".  

Dirt cheap as well, next Digikey order I'll include a few of those.

I have a PS1 locomotive with a buzz.  I've swapped everything out except for the speaker and the pot.  Guess I need to take a closer look at the speaker to make sure it's not bad.  GGG, what is liquid insulation?

Home Depot, RS sell it.  It is a black liquid rubber like stuff that is used to insulate bare wire etc...  Like heat shrink when you can't get heat shrink on a wire.  G

The buzz may be a bad capacitor, or the Voltage Regulator is failing and voltage is going high.  G

I'll have to check this stuff out the next time I'm at HD.

As for the buzz, I swapped out the boards, so if that is the case, I have several bad boards.  I've showed it to a couple of other guys and the conciseness is it's a grounding issue, a feedback loop like thing.  I have another speaker, but it's too tall to fit in the tender, but I have no other pots.  I do have another locomotive that is down I could try on to make sure I don't have bad boards.  Could you share what the location of the cap and VR are?

The VR is the one that normally has a bracket on it.  I think voltage should be about 9V out of it.  Some times they fail and go high causing issue with sound.

Capacitor is trial and error.  Just start swapping in known good ones on the bottom board.

At this point I would put a different top board in the bad engine and see if the static follows.  If static stays, I would than use a different bottom board with the original top board.  If still there at least plug a different speaker into the engine and then a pot, but the pot can be checked with VOM.  One direction one end to center is 0 and the other is 10K, vice versa when you rotate the knob the other direction.

At that point start looking how the wires are routed and making sure the motor leads aren't too close to top board or near speaker wires.  The other one is the battery lead.

Lastly if using a BCR try a battery instead.  G

Liquid Tape is great stuff, I use it regularly.  It's good for insulation, glue, and blocking out light from the back of LED's when I install them.