Vizio M420SL PS Issue

[nomoresonys]

Re: Vizio M420SL PS Issue

For good measure, while you are on the back of the board, check all your solder joints, maybe touch up any that look like they could use it, check the joints of anything on a heatsink, the ones on transformers take the most abuse, check those too.

[R_J]

Re: Vizio M420SL PS Issue

Can you post the numbers on the ic's, IC201 and IC601. Can you measure the dc voltage ACROSS ZD110 (near the printing "Attention Live Parts")
Using ZD110 anode, check the voltage on Q104 emitter (lead closest to C109) and Q104 base (lead near the !)
It is likely Q104 is the vcc switch for the two ic's above

[Jsikora]

Re: Vizio M420SL PS Issue

I think it is narrowed down to D603. It's an NXP NUR 460 Ultra-Fast and I do not have an equiv. so I tried a 3A and with that it did Power up and got the Vizio logo on the screen then it killed that diode. At this point I think I am going to order some of those and jump to the next TV. I will check those other readings but probably not get anywhere without having that diode in place.

[Jsikora]

Re: Vizio M420SL PS Issue

Will I be able to get anything at those points without having D603 in place?

[R_J]

Re: Vizio M420SL PS Issue

Ok, sounds like you have it located. A standard diode can't handle the high frequency of the pfc circuit.
I supect you would be able to check those voltages but if the tv did work to turn on the screen that circuit will be working as it must have turned on both the main and pfc ic's
I suspect once you replace the diode with the proper type you will get the +12 and +24 volts

[CapLeaker]

Re: Vizio M420SL PS Issue

So it is the pfc after all. The MUR460 is a ultra fast 4A 600V Diode, so you need either something equivalent or better. A lesser diode will just blow again. No you can’t get the TV working without the proper diode.

[Jsikora]

Re: Vizio M420SL PS Issue

Ordered the diode and crossing my fingers, hoping it soles the problem. Thanks for all your input and will let you all know the outcome.