Electronics > Repair

TV Switched mode power supply repair

(1/3) > >>

Deckert:
Hi guys,

I recently repaired a SMPS of an older LCD TV set. I documented the process in a 15 minute video below.

Something's been nagging at the back of my mind a bit. Close to the end, when I turn on the PSU and measure the DC voltage over the smoothing cap, it initially settles on 326V, which is expected with an AC feed voltage of around 230V AC.

However, when I turn on the set, the DC voltage increases to 400VDC and remains at that level. Since the cap itself is rated at 450V I'm not too worried, but is there any explanation as to why the DC voltage rises so much while in operation? Some distortion of the DC voltage, perhaps?



The set works fine though, and has been for at least a month, without any high temperatures on any of the components.

--deckert

ambrosia heart:
For any TVs with large panel, they will have a PFC circuit.
This explains why 400V is measured. :popcorn:

My TV is 24 inch. No such circuit. I don‘t want a TV as
large as a coffin  ;)

Picuino:
A PFC (Power Factor Correction) circuit is a Boost circuit.

https://toshiba.semicon-storage.com/info/docget.jsp?did=68570

Good video  :clap: :clap:

Deckert:
@Picuino: ha! thanks for that initial bit of info. the TLCD-32FHDA has a 32" screen, so no that big, but I get your point!  :)

@ambrosia heart: thanks for the linked document - really interesting reading, although I'm not fully grasping all of the concepts just yet. Saved for future reference.

As a matter of interest, I could not locate and of the more reputable capacitor brands that have the same specs and fit into the same form-factor, which tells me the original spec may have been inflated by the original capacitor manufacturer.

--deckert

wraper:

--- Quote from: Deckert on October 16, 2021, 01:05:27 pm ---As a matter of interest, I could not locate and of the more reputable capacitor brands that have the same specs and fit into the same form-factor, which tells me the original spec may have been inflated by the original capacitor manufacturer.

--- End quote ---
Those capacitors are not some very small size type which may be troublesome to buy. And Samxon is a decent brand.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version