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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?

thanks,

Bruce

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replace the regulators as i had suggested n you'll  be ok! LM337, and L7805 five volt regulator, Digikey has them in stock@

L7905CP STMicroelectronics | Integrated Circuits (ICs) | DigiKey

LM337TG ON Semiconductor | Integrated Circuits (ICs) | DigiKey

the FET is IRFI9Z14GPBF Vishay Siliconix | Discrete Semiconductor Products | DigiKey

Alan

Last edited by Alan Mancus

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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