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Have a B&O Budd car set, 30-2144-1, proto sound, that has a buzz coming from the speaker.  When initially powering up at about 5-6 volts there is no buzz, advancing the throttle to between 9-11 volts the buzz comes on, disappears, comes on again.  I understand this is a voltage regulator problem.  Have tried different speakers and volume pots, same thing.

Trouble shooting this is not covered in our Service Manual.  Can someone enlighten me as to what voltage regulator it is and the Digi-Key part number?



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Look for burned trace.  But to be clear.  With no battery attached does the sounds come on?  they should.  Even with a BCR not charging the engine should startup  on track power.  If it does not, you may not have LM337 working.  Didn't lift traces when replacing it?  There are several chips in the charge circuit, if the board works fine otherwise.  IRF does control it, but I think I have only ever replaced one of those.  Usually it is a trace issue.  G

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