Vizio E70-E3 will not power up

[busaboy]

Re: Vizio E70-E3 will not power up

From page 49 of the manual the regulators output is 3.39volts. Unfortunately the text is very distorted so I cannot tell how many parts are fed by 3.39volts. 3.39volts feeds a FET switch and yields 3.3volts. I'm going to pull the board, remove L201, back-feed 3 volts and see if I can get a cap to heat up or pop. Since it's not my TV and my buddy is unwilling to spend $100 for a used replacement, I'm gonna get medieval on the board.

[R_J]

Re: Vizio E70-E3 will not power up

I believe the voltage from U201 is 3.3v, V_3.3SB If that is the case it then feeds Q201 (switch) (page50) which is then called V_3.3M. It also feeds D632 (page 52)
So it would seem V_3.3SB is only for standby circuits and if there is no short after Q201 there are not too many components that are connected to that line.
If you have a bench supply that can supply 1~2 volts (or use a 1.5v battery) connect - to ground then momentarily ( a second at a time), touch the + to the V_3.3SB line, and feel around for a hot spot. some people spray an area of the board with alcohol which will evaporate very fast near the shorted component.

[dick_barton]

Re: Vizio E70-E3 will not power up

Use your meter set to ohms, set powered off and measure the resistance to ground at the following test points.

TP215 & TP219 (If I read them correctly since quite blurred)

[busaboy]

Re: Vizio E70-E3 will not power up

I believe the voltage from U201 is 3.3v, V_3.3SB If that is the case it then feeds Q201 (switch) (page50) which is then called V_3.3M. It also feeds D632 (page 52)
So it would seem V_3.3SB is only for standby circuits and if there is no short after Q201 there are not too many components that are connected to that line.
If you have a bench supply that can supply 1~2 volts (or use a 1.5v battery) connect - to ground then momentarily ( a second at a time), touch the + to the V_3.3SB line, and feel around for a hot spot. some people spray an area of the board with alcohol which will evaporate very fast near the shorted component.

I found V_3.3SB also feeds the IC on page 60. Going to pull L201 and apply DC.

Do you have a better copy of the manual?

[busaboy]

Re: Vizio E70-E3 will not power up

Use your meter set to ohms, set powered off and measure the resistance to ground at the following test points.

TP215 & TP219 (If I read them correctly since quite blurred)

I measure a "short" with a DVM at the switcher output capacitors. I'm guessing this is one of the TPs you mention. The text is so distorted every TP seems to be "TP215" :-(.

PS
I have an extensive electronics lab at my house. I can pretty much test anything. Attached is a few shots. Two guys from GE testing a digital radio for a locomotive...

[busaboy]

Re: Vizio E70-E3 will not power up

Use your meter set to ohms, set powered off and measure the resistance to ground at the following test points.

TP215 & TP219 (If I read them correctly since quite blurred)

I injected DC into the "output" of L201 because it looked like too much of a PITA to remove. I started with one power supply, then a bigger one and then a much bigger one (300watt). I injected 1 volts and then upped it to 2 volts. The circuit drew 6 amps with the PS on current limit. It took a lot of feeling with my hands but the problem seems to be a short inside the FOXCONN WiFi module. I will pull the shield off and see if I can fix it. Probably a bad cap in the module.

[R_J]

Re: Vizio E70-E3 will not power up

This is the only manual I have and I don't know why it is blurry, (some Panasonic plasma tv manuals are also like this) I did mention the module earlier as a problem, There is information on the module such as pinout.

[busaboy]

Re: Vizio E70-E3 will not power up

I traced the problem to the WiFi module due to the heat it was giving off from forcing current into the shorted MLCC cap(s). It must have gotten pretty hot inside the shield.

I replaced the 2 MLCC caps in the WiFi module and 2 MLCC on the output of L201 with cheap two 10uF axial aluminum electrolytic caps. The 2 MLCC caps on the output of L201 were OK but I didn't want to reuse them. Desoldering the shield off the WiFi module took a lot of heat from a 80 watt soldering iron. I didn't reattach it.

I cannot say which of the 2 MLCC caps in the WiFI module were shorted. I toasted the area pretty good with 2 volts at 6 amps as shown in the pic. The second pic shows the 2 caps. Lucky the vias and traces could handle the current. The TV seems to be working though I didn't check if WiFi is OK. Not my problem anymore....

[busaboy]

Re: Vizio E70-E3 will not power up

This is the only manual I have and I don't know why it is blurry, (some Panasonic plasma tv manuals are also like this) I did mention the module earlier as a problem, There is information on the module such as pinout.

Thanks. Unfortunately with the shield soldered on the WiFi module and the way the module was attached to the main PCB, it was difficult to locate the short.

I did find differences on my PCB. Q201 is a BJT versus a MOSFET in the schematics. I couldn't find Q202.

I wish I still had a special tester I made for finding shorts. It used a 10MHz oscillator feeding a 50 Ohm power buffer that fed a BNC connector. The BNC also fed a NE604 FM demodulator IC. I used the NE604 RSSI output (log amplifier), to drive a meter. With nothing connected the meter read maximum. As the impedance got lower, the meter reading dropped. It could find which connector was shorted on even a very short cable. It could find a short along a trace on a PCB. At 10MHz an aluminum electrolytic cap will have a higher impedance than a short. It would have found a shorted MLCC if I could get the probe close enough.

[R_J]

Re: Vizio E70-E3 will not power up

Thanks for the follow up, I suspect the mlcc are just for some filtering and the wifi likely still works.