DIYbanter - View Single Post - LN40A530 Samsung LCD TV long to start...Capacitor issue ?

mike[_22_]

On 6/9/2014 11:34 PM, wrote:
On Sunday, July 31, 2011 7:22:29 PM UTC-7, benitos wrote:
Hi ,

I have a LCD Samsung LN40A530 LCD TV that seems to have a capacitor
issue.

It takes 10 minutes to start.It`s getting worst with time.

I had checked all capacitors on the power supply board and they are
reading all good (value/ESR).

I even changed them and samething.

I have the service manual but there is no schematic and I don`t want
to change any board for nothing.

THe 5 Volts standby is OK. I read 5.2 volts.

Any idea ?

Your symptoms are classic for bad caps and unlike a fine wine, this will not improve with age

Many times there is a small ceramic cap i parallel with the 'lytic cap that will cause the ESR meter to say it's OK when it isn't. If the meter says it's bad it very likely IS.

Over the years I've observed that when I find a certain value/Voltage that has one failure in a unit, any other identical caps should be replaced as well. Generally when you get to the point of replacing some caps it's a good idea to replace ALL the 'lytic caps. Once you have the unit open it would be silly to gamble and maybe have to do it again.

Personally I prefer SMT caps as they're quicker to remove. I treat through hole and SMT the same. I destroy the cap by cutting it apart and with through holes, cut the leads on the component side down to the board with a flush cutter and the use an old solder sucker to pull the lead out the solder side. Remember to clean off any acid residue before installing the new caps and then the flux when you're done.

Also BUY THE BEST CAPS YOU CAN FIND. Your tine us way more expensive than even the best caps. DigiKey, Mouser, Newark and Allied carry good stuff. I usually use DigiKey because their website is more complete than the others and I generally get Panasonic caps looking for highest ripple current, highest hour and temperature.

G²

I've found the best test for caps is to stick a scope across them and
see what's happening to the voltage.
Isn't hard to tell if that node has an issue. If there are multiple
caps, it won't tell you which, but change 'em all anyway.

One thing that most people don't seem to realize is that a bad cap can
let the
voltage go WAY HIGH. If you're switching down from 20V to 3.3V, you can get
20V spikes on that node with bad caps.
I've had monitors DIE from the spikes.

The result of all that is...
Turn the thing off till you fix it. It may work after
10 minutes this time, but, eventually you may kill it.