Heat Sink Problem

[raster]

I noticed 2 large heatsinks that had a reading of AC 185v so im guessing these are live, is this right or should there be no voltage on heatsinks?

[mariushm]

Re: Heat Sink Problem

It depends on the power supply and how it's designed.

In general, it's not a good idea to have heatsinks live, it's recommended to have an insulating layer between heatsinked components and heatsink itself. In computer power supplies, usually the parts are already in a package that's insulated, or they use mica/other insulating foils and plastic spacers to insulate screws and heatsink from actual parts.

But any insulating layer will cause a degradation in the transfer of heat between parts and heatsink (by a few percent points), so in some applications it makes sense to just leave the heatsink live for better thermal dissipation.

My advice would be to check the parts and see if there was some insulating layer between parts and heatsink, maybe the insulating layer broke down or shifted and now the parts are live with the heatsink.

[stj]

Re: Heat Sink Problem

it could be capacitive coupling.

unusual voltage for a 230v supply.
does it have a 120/240v switch on it?

[raster]

Re: Heat Sink Problem

Thank you guys, the voltage above is wrong it's 216v sorry

[Alastair E]

Re: Heat Sink Problem

What make?

What model?

What fault?

What heatsink?

Prolly perfectly normal, Many sets have the heatsinks of psu at half mains potential or half PF potential.....

You dont tell us much! We aint psychics!!

[raster]

Re: Heat Sink Problem

its the heatsinks holding transistor and bridge rectifier 2 seperate HS but both live

[Alastair E]

Re: Heat Sink Problem

Oh Gawd--

WHAT MAKE??????

WHAT MODEL?????

Dear Oh Dear! IF you expect help and advice--You gotta give us INFORMATION!!

Its like saying-- 'What colour is my car' and expecting the Right Answer, when we've never even met you! I dunno!

[raster]

Re: Heat Sink Problem

its an LG eax40097901/15 sorry

[Alastair E]

Re: Heat Sink Problem

Err--

NO!

Make-- LG.

Model-- 32LF7700.

What You quoted is the Board Number!

I just Give Up!

Live heatsinks quite normal--bung the back on and forget about it!

[budm]

Re: Heat Sink Problem

Thank you guys, the voltage above is wrong it's 216v sorry

What is the problem with this unit you are working on?
What is the GND ref you are using when making DC measurement in the Primary side of the circuit? You cannot us the chassis as the GND ref in the primary side of the circuit. For AC in primary, you measure between Line (Phase) and Neutral.

[raster]

Re: Heat Sink Problem

Hi budm, wont power up but shows faint red standby light, nothing coming from this set at all. Yes i been using chassis as ground. When press power button faint red light blinks slowly 3 times and then no light,

[budm]

Re: Heat Sink Problem

Hi budm, wont power up but shows faint red standby light, nothing coming from this set at all. Yes i been using chassis as ground. When press power button faint red light blinks slowly 3 times and then no light,

So the standby power supply is working. What is the Model number of this LG TV?
How about uploading the pictures of the whole back side of the TV so we can see how all the boards are connected together?

[chrismurphy]

Re: Heat Sink Problem

I noticed 2 large heatsinks that had a reading of AC 185v so im guessing these are live, is this right or should there be no voltage on heatsinks?

If its the HOT side of the power supply, some are some are not .
Best not to touch any hot side components , I imagine you are looking at this as a safety concern not electrical

[Alastair E]

Re: Heat Sink Problem

Do you know what would have saved a LOT of confusion....?

--If you had said,---

'Ive got LG 32LF7700 that's dead apart from standby light thats dim.

BTW Heatsinks in PSU are at half mains potential, is this normal?.......'

Now we would know, the make, model And more importantly the Actual Fault!


Some heatsinks in PSU's are connected to B- of the main reservoir cap and always at half mains potential--Quite Normal.

Your original post suggested there was no fault--only the issue with live heatsinks......

[raster]

Re: Heat Sink Problem

i agree alistair

[budm]

Re: Heat Sink Problem

Please up load good clear pictures of the whole back side of the TV and the power supply board so we can see how all the boards are connected together.