JVC AV-28F3SJ-BF Replacement capacitor

[vinceroger69]

Re: Replacement capacitor

can you take a picture of what your seeing on the screen when you first turn the set on

[Ady2017]

Re: Replacement capacitor

Although it is a JVC TV, yes the PCB layout does look like that of the Vestel 11AK49. I heard that JVC just rebadge things these days.

The other IC looks like it is a tda8928j and part of the sound circuit so that is good, another thing eliminated.

I will get some pictures tomorrow but am studying the circuit diagrams at the moment trying to work out what is going where. Thanks for these, they are a great help.

[Ady2017]

Re: Replacement capacitor

Thanks for the schematics, they have helped understand the circuit a lot.

Excuse my ignorance but can you confirm that I am on the right line of understanding that the role of Caps C620 and C625 is to smooth fluctuations in the voltage coming from the transformer?

I assume the Caps C622 and C619 are there to further smooth the voltage?

What I am confused about is that Caps C623 and C626 are connected to the same transformer output but rated to a different voltage?

[R_J]

Re: Replacement capacitor

Caps c620 and c625 filter (smooth) the a/c that comes from the transformer and is then rectified to dc by the diodes.
c622 and c619 are to remove any high frequency component that is not filtered by the other larger capacity capacitors.
C623 and C626 are both rated at 50 volts. or do you mean compaired to the 100v rating of the c622 and c619, It could be that they would see a higher voltage spike or it could be just the value the mfg put in. 0.1uf (100n) at 100v is actually fairly low voltage rating for those type of capacitor.

[Ady2017]

Re: Replacement capacitor

I am on the right line of understanding then. The caps connecting the voltage tracks to ground are acting like an inductor to smooth the voltage but will be doing a better job at smoothing the voltage. Under normal operation, the caps will be fully charged then at which point they will have an high resistance preventing the power simply discharging to ground. It them makes sense that when the cap goes bad that the power will leak to ground and the voltage drop in the power line.

[budm]

Re: Replacement capacitor

"The caps connecting the voltage tracks to ground are acting like an inductor to smooth the voltage but will be doing a better job at smoothing the voltage. Under normal operation, the caps will be fully charged then at which point they will have an high resistance preventing the power simply discharging to ground. It them makes sense that when the cap goes bad that the power will leak to ground and the voltage drop in the power line."
Inductor works in opposite from capacitor, inductor block high frequency, since the cap is connected between Voltage supply line and Gnd then it cannot be acting like inductor otherwise it will not be filtering.
The capacitor will have to supply the Voltage when the Diode is turned off during the AC cycle, if its capacitance drops then you will have more AC ripple riding on dc Voltage.
https://www.electronics-tutorials.ws/diode/diode_6.html

You should also search what the inductor is and its characteristics, same for capacitor.

https://electronics.stackexchange.co...rs-in-parallel

"Utilize different capacitors for decoupling different frequencies: A single capacitor is not always able to remove all the frequencies that may be present on a voltage supply line etc. To fully achieve this, it is often the practice to use two capacitors in parallel: one such as an electrolytic with a larger value to remove the low frequency components (the electrolytic capacitor is not good at passing high frequency signals); and one such as a ceramic capacitor with a smaller value for removing the high frequency components (the smaller ceramic capacitor will not have a low enough reactance to pass the low frequency components).

[Ady2017]

Re: Replacement capacitor

Thank you all for your feedback and patience. This has been an excellent learning exercise by looking at actual real-world circuits and working out how they work. It is like working on your car. Before you can fix it, you first have to determine how it is meant to work.

I am currently scrolling through amazon looking for a good book to learn more. Every book seems to have reviews saying each one is the best book ever which makes it difficult to find the best one to go for. Does anyone have any recommendations?

[Ady2017]

Re: Replacement capacitor

Thought I would keep you all updated. Managed to fix the TV and it was a bad capacitor. The capacitor was showing as being ok with the basic tests with a multi-meter and there were no visual signs of damage. Learnt something new, to just swap it out.