Toshiba TV low voltage on PSU

[DjKrish]

Hi all. Just managed to diagnose a toshiba regza 40 inch power problem that resulted in no picture and no sound. Was checking throughout the voltages and noticed 12v and 24v was very low with load. Knew some caps popped somewhere. Started checking all the caps and noticed the main 2 filter caps was leaking. Went to parts store, didnt manage to get the exact same size which is the long type according to the picture but got a bigger one instead and with same uf and v which is 68uf 450v. Soldered it and tested the unit, works perfectly fine.

But have 1 problem here. I am hearing a eeeeeeee buzzing sound near the caps or the transformer. But the unit works fine. What can be wrong? Can i use a bigger size capacitor or i have to use the same exact size?

According to the picture, the long black one is the faulty cap and the short fat one is the new caps.

Note : There was no buzzing sound before replacing the new cap. After replacing cap theres buzzing sound.

[Andrew F. Ali]

Re: Toshiba TV low voltage on PSU

Once you have the space to accommodate the bigger e-caps that wouldn't be a problem as they are the same uF and WV as the original. Reflow the transformer pins onto the PCB sometimes while handling they develop fine cracks that can produce buzzing sounds. Look too at the other heavy solder connections on the PCB, heat sinks, etc. The buzzing sound though is not a problem though. Unless it is loud and unbearable.

[DjKrish]

Re: Toshiba TV low voltage on PSU

Once you have the space to accommodate the bigger e-caps that wouldn't be a problem as they are the same uF and WV as the original. Reflow the transformer pins onto the PCB sometimes while handling they develop fine cracks that can produce buzzing sounds. Look too at the other heavy solder connections on the PCB, heat sinks, etc. The buzzing sound though is not a problem though. Unless it is loud and unbearable.

It is quite noticeable. quite sharp beeping.

[Andrew F. Ali]

Re: Toshiba TV low voltage on PSU

Did you do the re-flow? That buzzing most likely is off the Transformer and other Coils.

[DjKrish]

Re: Toshiba TV low voltage on PSU

Yes i did. Still same. The thing is, the sound wasnt there with the old cap. Only started with the new cap. Afraid something to do with the size of the cap. Maybe its too big? Overloading? But the voltage and value is same.

[Andrew F. Ali]

Re: Toshiba TV low voltage on PSU

Then you should not have a problem. No overloading and nothing to do with the size.Tighten ALL hold down screws on the PCBs. There is something loose. Perhaps the cap is resting on something and vibrating. I don't have photos, neither is the PSU in front of me and I don't know if this is a CRT, LCD, LED or Plasma TV or size of TV we are dealing with. Unless the Transformer core is broken/cracked.

[DjKrish]

Re: Toshiba TV low voltage on PSU

Its a toshiba rega led tv, slim series. So basically ure saying, it doesnt really matter whatever size the capacitor is aslong as its the correct value. Right?

[Andrew F. Ali]

Re: Toshiba TV low voltage on PSU

Yes.

[DjKrish]

Re: Toshiba TV low voltage on PSU

Manage to replace original caps at a very affordable cost. However, the transformer still giving a high pitch sound. Its the Ac transformer, not the DC. U can actually see it in the first post photo. The yellow color. The sound is definitely coming from it. But no problem with all the voltages, all accurate. Already soldered all the cold joints. Still no change. TV is working perfectly fine now. Just the sound.

When i put my ears really close to the pitching sound, it sounds like more coming near the capacitor. Also with the high pitch sound, i hear a faded tuner sound. Of course i had unplugged all the speakers. The sound coming from the marked area.

[Andrew F. Ali]

Re: Toshiba TV low voltage on PSU

If you re-read my Post Nos. 2 and 4 I spoke about the transformers...Took you really long to finally agree that the buzzing sound is coming from there. OK so you changed the e-caps to the ' original' ones. Did it make a difference?? NO....And you re-soldered the transformer legs and all the heat sinks attached to the board. What is it then exactly you want?

[DjKrish]

Re: Toshiba TV low voltage on PSU

The sound, its very annoying though. Here let me give u a youtube video of how it sounds like.

https://youtu.be/FcniCVgOJL0?t=165

Skip to 2.45

[budm]

Re: Toshiba TV low voltage on PSU

That is the inductor for the PFC Voltage booster circuit, the buzz can be cause by bad PFC controller IC.

[DjKrish]

Re: Toshiba TV low voltage on PSU

That is the inductor for the PFC Voltage booster circuit, the buzz can be cause by bad PFC controller IC.

I tried finding for the service manual but no luck.

[DjKrish]

Re: Toshiba TV low voltage on PSU

That is the inductor for the PFC Voltage booster circuit, the buzz can be cause by bad PFC controller IC.

But the TV is working perfectly fine. Every voltages are accurate. Its just that im afraid this noise IN TIME will kill other components due to a short or something. If u close the cover, you can still hear the noise from outside though. Could it be the ac capacitor?

[DjKrish]

Re: Toshiba TV low voltage on PSU

Ok my friend gave me a similar board and i replaced the transformer, still same with the sound. Changed the capacitor as well. Same sound. Now my only solution is to replace the PFC controller IC and see if that solves it as suggested by budm.

Question. Do i short the PS ON with ground to test voltages? Cause i want to test it standalone without main board help.

[Andrew F. Ali]

Re: Toshiba TV low voltage on PSU

Why would you want to test the PSU stand alone?...it would only tell you what you already know...that is PSU developing all the voltages to work the TV. As BUDM suggests the buzz could be due to a bad PFC controller IC. I would suggest you replace this before attempting to do anything that may wreck your PSU.

[DjKrish]

Re: Toshiba TV low voltage on PSU

Why would you want to test the PSU stand alone?...it would only tell you what you already know...that is PSU developing all the voltages to work the TV. As BUDM suggests the buzz could be due to a bad PFC controller IC. I would suggest you replace this before attempting to do anything that may wreck your PSU.

The main reason i wanted to do that was i wanted to know if the main board is triggering the psu to make that noise due to voltage or something. So thats why i wanted to start up the psu without the main pcb and see if the noise is there. Yes, im gonna swap the PFC IC and try. Keeping my fingers crossed that its the PFC thats giving the problem. Will update here once i swapped it.

[Andrew F. Ali]

Re: Toshiba TV low voltage on PSU

I don't think the Main Bd can cause the PSU to make noises. The Main Bd generate signals to turn on the PSU, turn on the BL, Dimming control, LVDS and send power to the T-CON Bd from the PSU or Main Bd itself.

[Th3_uN1Qu3]

Re: Toshiba TV low voltage on PSU

That noise is likely caused by oscillation of the feedback loop of that controller IC. It could be by (poor) design and throwing parts at it will not fix it - understanding what goes on and modifying the circuit slightly to get rid of the oscillation, will. Some power supplies just whine from the day they were born. If it gives the correct voltage output and the ripple is in spec, a lot of times they will let them go like that.

Control loop theory is unfortunately complicated, even I do not understand it fully, but if you give me a schematic i can try to figure out where you could start.

The good news is that it will likely not cause any issue in the long run, it is just audibly annoying and that's it.

[DjKrish]

Re: Toshiba TV low voltage on PSU

I just replaced the PFC IC from the other faulty board, looks like the other one is faulty as well but no noise, just blinking standby red LED. I fixed back the original PFC, the noise is there. Ive ordered a new PFC which is FAN7530. Oh well, we shall see what happens when i replace the new one.