Vizio E28H-C1 Repair

[Fisher77]

Here is another one that was zapped by lighting at my parents house. I found FET, resistor , and a diode blown.
Replaced all, plugged back in and blew the resistor and the FET almost immediately.
Before it blew I managed to measure some voltages on the output of the power supply.
Funny thing was they were AC voltages, not DC.
Pictures of the power supply board attached. The blown FET, and resistor have been removed.
I have not been able to locate a schematic for this power supply.


https://i.imgsafe.org/bd48c1ba67.jpg
https://i.imgsafe.org/bd48f552f7.jpg

[Fisher77]

Ok, I have checked over this board. I cant find noting shorted. Has to be something shorted to blow a FET and Resistor.
Anyone have any suggestions?

Thanks

[Fisher77]

Anybody have a suggestion on what I could check?

[KhronX]

As i just mentioned in the previous thread (before noticing this one), chances are good the PWM controller's shot as well 

[Fisher77]

As i just mentioned in the previous thread (before noticing this one), chances are good the PWM controller's shot as well 

I didn't think about the PWM being bad also. Only makes since that it would be. I will check it.

[tautech]

Check ALL the diodes, primary and secondary sides and lift one lead if you need to.
Check the 2 caps near the FET, one will be the bulk storage for the controller IC and they are known to degrade with time.
Study the controller IC's datasheet for a "Typical Application" schematic that is often copied closely in designs.
Understand what undervoltage lockout means and how to check for it.

AND make yourself a Dim Bulb tester that only an incandescent bulb in series with the mains supply. You will be rewarded if you do in saved componentry as it will prevent full mains current from destroying parts in the primary side. Google it for more understanding. 

[Fisher77]

Ok the PWM on the PS board is a PF6003AS. I can't find a datasheet for it. I did a google search, but didn't come up with anything. Anybody have an idea where I can find a datasheet for it?

I found a replacement on aliexpress. It is a PF6003AHS:
 
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20170112142410&SearchText=+PF6003AHS

I found this data sheet while searching for the PF6003AS:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiIlPCO973RAhWollQKHTDBA70QFggcMAA&url=http%3A%2F%2Fwww.syncpower.com%2Fdatasheet%2FSP6003A.pdf&usg=AFQjCNG0XoutbmCAbsZ6_-yRD80TuQkIyQ&sig2=8zFY0bFHpPoj0qAvb-hR-Q

It is a SP6003A. Is that the same thing?

[KhronX]

For what it's worth, the UC384x series of chips has been cloned and rebranded with several other prefixes (replacing the "UC" part), although that's no real guarantee this is the case for those chips as well.

I just checked that last link, and you can bet your booty it's not the same part. Preeeeetty big difference between "PWM controller" and "synchronous rectifier driver" 

But then again, for a buck a piece, getting a few from aliexpress might just be worth it, if you can stomach the month-long wait...

[Fisher77]

But then again, for a buck a piece, getting a few from aliexpress might just be worth it, if you can stomach the month-long wait...

A month wait is no joke. The LD7575 that fixed the westinghouse was ordered on Dec. 17th. I just got it today. As suggested by tautech, I checked all the diodes, and the caps. No problem found with any of them. Looks like I may have no choice but to wait another month .

[KhronX]

That's the trouble with cheap stuff (ie. damn near "no-name" brand electronics) - they often use some obscure components you can only get from the (let's call it) "grey market" 

[Fisher77]

Part ordered from the "grey market". I wll post back in a month.

[Fisher77]

Well the PWM came in. I installed it this morning. Still now go. I found the pic below that shows the pinout or the PWM PF6003AHS . Checked the voltages at the PWM, and they are all present. Any idea's?

[tautech]

Well the PWM cam in. I installed it this morning. Still now go. I found the pic below. Checked the voltages at the PWM, and they are all present. Any idea's?

If you study how the VCC is supplied there might be a clue there, the dropper resistors being of such high values might have trouble passing enough current if the IC's VCC bulk cap is leaky and therefore maintaining a voltage over UVLO could be a problem. I normally replace the IC bulk cap as a matter of course, but I'm surprised they use only 4.7 uF, 20-50 uF are more common values.

[Fisher77]

Well the PWM cam in. I installed it this morning. Still now go. I found the pic below. Checked the voltages at the PWM, and they are all present. Any idea's?

If you study how the VCC is supplied there might be a clue there, the dropper resistors being of such high values might have trouble passing enough current if the IC's VCC bulk cap is leaky and therefore maintaining a voltage over UVLO could be a problem. I normally replace the IC bulk cap as a matter of course, but I'm surprised they use only 4.7 uF, 20-50 uF are more common values.

I posted that pic just to show the pinout of the PWM. I should have explained that, fixed the post. I replaced both of those electrolytic caps. Still no go. At this point I have replaced the FET, PWM, both electrolytic caps, a resistor, and blown diode. Any other ideas?

Which way am I supposed to check the voltage on the PWM, AC or DC?