Hello there,
I would like to get some help, or at least educated tips for one of my current repairs. I bought a faulty 27″ curved samsung monitor which did not have any image. After couple hours of troubleshooting (I am doing this repair at my students dorm and not in my workshop, thus my lack available equipment makes the troubleshooting more timeconsuming) I found a ceramic capacitor with a value of 37 Ohm across it. This capacitor was on a 17,3 Vdc rail which powered some control electronics and also was later stepped up to 26 Vdc for more circuitry.
Failure if the mentioned capacitor pulled the 17,3 V rail down quiet heavily and as a result the step up converter for 26 V did not have enaugh voltage at the input, struggled to work a died (all switching power supply rails are controlled by one IC that is impossible to get separately). Once I figured this situation out, I installed a separate step-up converter module at the 17,3 V rail to generate the 26 V voltage. This fixed the problem and I got my screen image back, but new issue rise. The two switching converters connected after each other probably do not like each other very much and there is “whine/scream” comming from either the inductors of ceramic caps.
Can anyone here give me some hints or tips as to what I can do to remove the switching whine? I am very happy, that I get picture back, but with the enoying sound coming out of the device now, it is unusable.
Thank you in advance for any help or advice. 🙂
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P.S.
I tried adding a ferrite core around the wires and adding 0.1 uF ceramic caps across all inputs and outputs as close to them as possible, but this did not work.
Update: Problem SOLVED.
Yesterday I tried to install a different boost converter module, which had large’r electrolytic capacitors at the input and output and it seems like those did the trick. Meaning my initial steps were the opposite of what I supposed to do. I tried installing small value ceramic caps, but instead I should have installed some at least 10 uF caps. Now everythink is dead silent.
Here are some pictures of my hack-isch repair – but if it works, it works and I do not think it should fail in the future. Simply – when the manufacturer does not offer replacement parts, you have to walk around the simples solution.
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Functioning monitor 🙂
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@honzam I was going to say, up those values! Did you determine if the cap itself was bad or something else in the circuit? Also since you added a separate supply, did you disconnect or disable the old supply? Not sure if they would fight each other. Good job working through the problem
Radios + Tubes + Scopes + Cars= Nothing better!
@radtekman Thank you for your feedback. It was a valuable lesson for me, this repair journey.
A tracked the original failure all the way to the culprit – the ceramic cap. After it failed however, it took the 26 V rail with it. It is interesting, because the bad cap was not on the 26 V rail, but it was on a 17 V rail, which was later stepped up to the 26 V. After the failure, 17 V was still ok, but 26 V was gone.
There is one SMPS driver IC taking care of four different voltage rails, one of them being the 26 V. All the rails except that one were ok after the failure.
And yes, I disconnected all circuitry connected specifically to the 26 V boost converter part of the original power supply circuit.