Small speaker not working - Page 1
Forum section: electronics / repair

author: Nexo
author_rank: Regular Contributor
timestamp: December 29, 2017, 09:40:27 pm
content: Hello everyone!I've been trying to figure out what's going on with a speaker I have, is a small one and is not working. What I tried was this:1. Make sure that the cables that connect to the mains are working correctly. They are.2. Make sure that the trasformer is stepping down the voltage from ~110V to ~12V. It is.3. Make sure that the cables which connect the transformer to the bridge rectifier are working correctly. They are.4. Test the bridge rectifier. Here is where I have a problem because when the speaker is turn off I test continuity in every diode but the meter doesn't beep. Am I testing it right?5. Another thing is that this circuit is small and has a potentiometer with an on/off switch just like the one showed in this page:https://www.adafruit.com/product/3393And it's a bit weird because when the knob is in the off position, there is continuity between the brige rectifier's cap's terminal but when is in the on position, there is not. Plus, when I turn on the speaker (being connected to the mains) and measure the voltage between the bridge rectifier's AC input it shows only 2.4V AC but when I place the know in the off position, it shows 11.4V AC. Maybe is a short circuit or something?Then, I touch the diodes and sometimes one gets really hot but other times it doesn't. It's quiet confusing to be honest.I'll upload a few photos in a bit.Thanks in advance for your comments!Edit: To add 2 photos

author: barry14
author_rank: Regular Contributor
timestamp: December 29, 2017, 10:20:43 pm
content: Could you provide some information on what this board does, a schematic, and what kind of speaker. How do you know the problem is the speaker?

author: Electro Detective
author_rank: Super Contributor
timestamp: December 29, 2017, 10:26:36 pm
content: The yellow amberproduct sab0tageglue on the components would be my Number #1 suspect,heated up and picked off VERY carefully and patiently bit by bitbefore continued troubleshooting.Tip: Cut and pick off the darkest amber blob first on the left side and test the speaker, before continuing on.It looks like a giant link bridge, perhaps across components likely to get warm and mis-behaveYou might find the device comes back to life immediatelyor at best expose a corroded part or PCB trace, and or a partial intermittent bridge/short due to the reaction with the glueEither way, ALL the yellow glue has to go, otherwise it will always bite you in the future as it heats, cools and eats away at the components and or shorts themClean up with non residue alcohol and use a clear hot glue/gun to secure components that need it once you're back in business,and good luck

author: Nexo
author_rank: Regular Contributor
timestamp: December 29, 2017, 10:37:22 pm
content: Quote from: barry14 on December 29, 2017, 10:20:43 pmOf course!Here is an image explaining a bit this circuit.

author: Nexo
author_rank: Regular Contributor
timestamp: December 29, 2017, 11:19:02 pm
content: Quote from: Electro Detective on December 29, 2017, 10:26:36 pmI did what you told me, did my best but it's still not working. I tested the diodes with a multimeter and it gives me readings no matter the polarity, all 4 of them. Are they damaged?

author: Electro Detective
author_rank: Super Contributor
timestamp: December 29, 2017, 11:27:41 pm
content: All the glue gone?cable prod and tidy with a wooden toothpick?Use a magnifier just in case a cable whisker is touching somethingOtherwise you have a component fault somewhere, or everyone's favorite...cold solder joint/s