Vizio vo420e no 12v

[R_J]

Re: Vizio vo420e no 12v

Ok it's U601 ( you have the board, we have a picture). 30Ω seems low, I suspect the fan7530 is bad. and Q101 will also be bad.
The fan7530 has an internal zener and should run at about 12 volts VCC
I would also check the two fets that the fan ic drives, make sure they are not shorted.
Q101 is likely a KST2222a

[budm]

Re: Vizio vo420e no 12v

Yes, the IC U601 (PFC IC), it is either internal shorts or the filter caps on the VCC pin, especially the MLC Cap type, i.e cap c602 on pin 8. So check the caps connected to the VCC pin.

[shadetreetrader11]

Re: Vizio vo420e no 12v

Parts showed up today. The PFC IC U601 was a Digi-Key P/N FAN7530MXCT-ND and the transistor Q101 was a KST2222AMTFCT-ND. I ended up using a different cap from a parts board for C602. Just finished installing them and I now have 12v!!! Thanks guys for guiding me threw this step by step. Tomorrow morning I'll install it in the TV and let you know if we have success.

[shadetreetrader11]

Re: Vizio vo420e no 12v


So just installed the PSB in TV and the backlight flashes for maybe a second or two and then stays off. I used a flashlight and I can see a "no signal image" on the screen. I can also pull up the menu screen and toggle threw that. I guess I need to figure out if the inverters are working but not sure how to do that.

Tv off
168v on main caps

dim-0v
inv on-0
vbr_a-0
blank
status-0
blank-0

on/off-0
12v-0
12v-0
12v-0
gnd
gnd
gnd
gnd
gnd
st/5v- 5.19
st/5v-5.19
st/5v-5.19

TV ON
168v on main caps I monitored this the whole time and it never changed.

dim-2.90
inv on- 3.28
vbr_a- 1.35
blank
status- 3.27
blank-0

on/off- 3.19
12v- 12.
12v- 12.
12v- 12.
gnd
gnd
gnd
gnd
gnd
st/5v- 5.19
st/5v -5.19
st/5v -5.19

[ARGO]

Re: Vizio vo420e no 12v

It looks like you have problem with LED strips... Measure output voltage to LEDs when you turn on TV

[shadetreetrader11]

Re: Vizio vo420e no 12v

What should I expect for a voltage? I'm using the frame for ground and I'm probing on the wires coming from the two transformers to the back lights. I set my meter to min/max mode. I'm not seeing much for a voltage. Around 0.6 volts. I must be doing something wrong becouse the lights flash for a second or two and I'm not seeing it on my meter. Using a fluke 115.

[R_J]

Re: Vizio vo420e no 12v

The voltage from the transformers is high frequency A/C. You can not measure it with your meter.
You likely have one or more bad ccfl tubes in the panel
Disconnect one of the plugs and see if you still get the backlight flash. If you do, connect that plug and disconnect the other plug and try it again. If you get the backlight to flash in both tests it is very likely the board/inverter is ok

[shadetreetrader11]

Re: Vizio vo420e no 12v

RJ, I just performed your test and it does flash from each inverter. So I guess tonight I tear it apart. I'm just really surprised that I had a issue on the psb board and at the same time backlight issues. Wonder if it was hit by lightning or something

[R_J]

Re: Vizio vo420e no 12v

Does your pfc voltage on the large cap go from 160v to 300 plus volts when its turned on?

The ccfl's could be ok, I thought you replaced the power supply board but now that I read back I see you repired it.

I guess there still could be a fault with the power supply board not keeping the inverter section turned on. It is either seeing a fault with the ccfl's giving an error or the inverter drive ic thinks there is a ccfl error but that could be caused by the return circuit having a problem.

[shadetreetrader11]

Re: Vizio vo420e no 12v

No, it stays at 168v. Caps are rated at 450v

[shadetreetrader11]

Re: Vizio vo420e no 12v

Before I go tearing this thing all apart and risk breaking the screen. Is there something else I can test?

[budm]

Re: Vizio vo420e no 12v

At this point you need to find out why the PFC Voltage booster is not working, it should be around 380 ~ 400V range, you should leave the meter probes on the tow legs of the main filter cap then turn the Tv on while watching the meter to see if it eve jump up from 160V to higher than 300V or not.
PFC IC U601 (Digi-Key P/N FAN7530MXCT-ND) is that IC getting the VCC to run?

[CapLeaker]

Re: Vizio vo420e no 12v

Before I go tearing this thing all apart and risk breaking the screen. Is there something else I can test?

fix the pfc on the psu. again, it still isnt running. that has to be fixed first. you can dl the datasheet of the pfc controller and see what voltages should be on what pin.

[budm]

Re: Vizio vo420e no 12v

BTW, did you check the MOSFET for the PFC and also the resistor connected to the Source pin of the MOSFET PFC, you should also re-inspect the soldering works on that PFC IC just to be sure.