Lg42lb5 no standby or turn on

[dick_barton]

Re: Lg42lb5 no standby or turn on

The power supply may have a varistor in the supply line on the circuit board to stop inrush current. That would be worth checking out if there's one present. Otherwise as said check the DC voltage across the large capacitors. In the UK it's around 340V dc so 400VDC capacitors in circuit. If you don't have a good DC voltage across at least one of the large capacitors then I would use the ohm meter and trace the live and neutral tracks for an open circuit.

Edit.
But you say you have a voltage at the bridge rectifier and nothing on the larger capacitors. It could be that these will not have power until the 5V standby is up and running to switch in the relay to connect the output of the bridge rectifier to the capacitors.
Is there another bridge rectifier circuit on the board that feeds the 5v standby circuit?

[snake91876]

Re: Lg42lb5 no standby or turn on

How do I check the DC current correctly on large filter capacitors. I want to make sure I'm reading them right.

[dick_barton]

Re: Lg42lb5 no standby or turn on

Hello Snake91876,
Take a look at the capacitors. They give a value eg 2200uF 350V, or 1uF 50v. Place your meter probes across the two terminals of the capacitor with your meter set to DC and take a reading. Bye the way do you have any dc voltage on the output terminal marked 5Vs?

[mmartell]

Re: Lg42lb5 no standby or turn on

@snake you must be very careful taking readings on the primary side - do not let your probes slip as these will be connected directly to the mains !

[snake91876]

Re: Lg42lb5 no standby or turn on

I have 50v DC on each of the big filter caps , and no voltage at 5vs. From a ground to one leg of cap I get 102v reading like at the bridge rectifier.

[CapLeaker]

Re: Lg42lb5 no standby or turn on

not sure man, but your readings are screwed up. Get a new meter or borrow one. I don't trust it.

[mmartell]

Re: Lg42lb5 no standby or turn on

Are you taking readings with reference to ground in the primary ? Can't do that. For the large filter cap put your probes on each leg of the cap. Apologize if I've misunderstood.

[snake91876]

Re: Lg42lb5 no standby or turn on

Measuring across caps I have 50 v DC leg to leg

[jetadm123]

Re: Lg42lb5 no standby or turn on

To make sure people are not going down the wrong path, perhaps you can check the accuracy of your meter using a flashlight or 9V battery.

[snake91876]

Re: Lg42lb5 no standby or turn on

I have checked meter

[halobender]

Re: Lg42lb5 no standby or turn on

I'm with jeadm124t something seems screwy. There should be around 170v on that main capicitor with the set plugged in but not turned on and seeing 50v is rather strange. If that cap is truly measuring that I would replace it. When checking your 5v be sure you are testing hot to chassis ground. Not earth ground.