Original Proto Sound Boards - buzzing noise from speaker

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

Thanks, Allan.  Parts are on order, will replace all three.

Why replace all three?  A battery control, the 5V, and the regulated 9V?  Measure the output.  I bet the LM337 is the culprit and no longer regulating voltage.  As you raise track voltage the reg goes high and induces static.  G

George,

I replaced the LM337TG voltage regulator and the battery charging terminal 24 ohm resistor.  Sounds come up when I install a charged battery but not with a BCR needing charging.  Seems the battery charging circuit is not working.  Is this a defective LM337TG or the L7905CP or a defective FET  IRF19ZGTBF?

Bruce

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

Traces are ok, no cuts, no burned spots.  Today I replaced IRF19Z - that did the job.  Looks like we found a solution for a noisy speaker.

Bruce

How did you find one of those?

@bruce benzie posted:

Traces are ok, no cuts, no burned spots.  Today I replaced IRF19Z - that did the job.  Looks like we found a solution for a noisy speaker.

Bruce

Why do you think that fixed a noisy speaker?  The regulator fixed that, then you had a battery charge issue.  That was fixed by the IRF chip.  Missing the correlation? G