VZ42L No Amber light, no stand by 5v

[Bigredram87]

Re: VZ42L No Amber light, no stand by 5v

Also I'm trying to grasp the circuit concept so far... Does PSON come from logic board that 3 volts powers the opamp SOP chip that chip boosts voltage(14v) to the (vcc) Pfc Ic which outputs through diode I just replaced and powers the MOSFET ? Is that correct

[tom66]

Re: VZ42L No Amber light, no stand by 5v

The Vcc is generated off the auxillary winding from the standby transformer.

A transistor on the primary side is switched on using the opto coupler's internal transistor (the optocoupler is turned on by passing a current through its isolated LED, controlled by PSON.) The transistor then provides the PFC chip with Vcc which causes it to operate.

That is how it usually works.

[Bigredram87]

Re: VZ42L No Amber light, no stand by 5v

Ok great Is the opto isolater a 8 pin smd chip? Im trying to find it

[tom66]

Re: VZ42L No Amber light, no stand by 5v

Opto typically four pins in rare cases 6 pins and crosses the isolation barrier. (between hot/primary and cold/secondary)

[Bigredram87]

Re: VZ42L No Amber light, no stand by 5v

Ok i found them. You dont have to answer i could continue to research on my oen but i figured you would know my answer. I was never taught opto isolaters and after looking on wikepedia im a little confused can you give me a rundown of what the isolaters are actually doing in this circuit? Sorry for the possibly stupid question

[tom66]

Re: VZ42L No Amber light, no stand by 5v

Optical isolators are a method of transferring an analog signal across an optical barrier. Since there is no electrical connection between the two sides of an opto in typical usage, the two sides can be isolated yet transfer information. The information can be a feedback signal, as part of the power supplies' regulation loop, or it can be an on/off signal.

Current flowing through the opto LED (A-K) causes current to flow along the opto transistor C-E. If you understand transistor operation, think of it like a current flowing into the base of the NPN transistor except instead of electrons it is photons from the LED activating the transistor causing it to conduct. There is a ratio, called the current transfer ratio, which determines how much current can flow through the opto transistor for a specific opto LED current.

Isolation of the two sides of a power supply is an essential safety feature and must always be preserved. A typical power supply can survive in excess of 2kV between the two sides without the isolation barrier failing.

[Bigredram87]

Re: VZ42L No Amber light, no stand by 5v

Great! That just "clicked" for me.

[Bigredram87]

Re: VZ42L No Amber light, no stand by 5v

My new MOSFET comes tomorrow but in the meantime I'm having a hard time understanding the difference between a bride rectifier and a filter choke. From what I've read the waves look the same ? Thank you

[Bigredram87]

Re: VZ42L No Amber light, no stand by 5v

Ok installed new MOSFET . The tv flicked on for a second read no input(because there isn't ) and flipped off? I measured voltage across big capacitor and it is at about 360v where should I go from here? There is still nothing at the 12v pins ? What voltage should I be measuring at the MOSFET pins ? Thanks so much

[Bigredram87]

Re: VZ42L No Amber light, no stand by 5v

Pin 1 of MOSFET measuring -59.00v pin 2 74v pin 3 -59.00v

[tom66]

Re: VZ42L No Amber light, no stand by 5v

Where is your ground?
360V is OK for 115VAC PFC, I have seen some designs use that as a target voltage.

[budm]

Re: VZ42L No Amber light, no stand by 5v

It sounds like he is using the Chassis as the Ground ref instead og the Negative leg of the main filter cap, but so far it does look like the PFC is working, just have to find out what else are not working.

[Bigredram87]

Re: VZ42L No Amber light, no stand by 5v

Got it! One of the pads on the Pfc were lifted I finally found a microscope to see it. Thanks so much I really appreciate all your help.

[tom66]

Re: VZ42L No Amber light, no stand by 5v

Does it work now?

[budm]

Re: VZ42L No Amber light, no stand by 5v

"The tv flicked on for a second read no input(because there isn't ) and flipped off?" It will go into standby if it does see video signal.

[tom66]

Re: VZ42L No Amber light, no stand by 5v

Yes, Vizio are know for doing this... usually 5 or 10 seconds max.

[knoxrebel]

Re: VZ42L No Amber light, no stand by 5v

Just finished repairing one of these boards. No visible signs visible damge or bulging from caps. No 5v standby voltage. Tested diode on board and it tested continuity in both directions. Tested out of circuit to confirm and that was the only bad that failed