TV Repair - Accidentally brought to life (momentarily) with DMM!

joshzstuff

New Member
I was probing voltages on the pins of the TVs Logic board (going to the Time-Control Board) and suddenly it came to life!
The power supply did not sound healthy to me, but maybe I'm mistaken.
I'm trying to get the video uploaded to listen to the sound it makes.

After I power cycled the TV it was was dead once again and I could not reproduce the probing that brought it to life.

Specs:
Vizio LED TV E70u-D3 (70")
Info PDF https://support.vizio.com/s/article/E70u-D3-Model-Information?language=en_US

Original Problem:
It was reported to me that the TV became increasingly unstable.
It would turn itself off after just a few minutes, and there was distortions on the screen.
Finally the TV would display nothing at all.
The power cable was replaced, and the TV was power cycled. Both attempts seemed to correct the problem, however now the white power LED will illuminate for a few seconds and go out after a minute, there is no longer any display shown on the screen.

Trouble shooting Technique.
I intend to check all the power supply capacitors, then move to stand by power, voltage regulators, and voltage levels on other boards.

The red label "12.3V" is the pin I was probing when the TV came to life.



With the TV plugged in, but in stand by mode, there is 0volts on these pins, however after the power button is pressed 4/7 of them get 12.3 volts.
I was checking this when all the sudden the power supply booted up (noisily) and the screen lit up.
I was able to feed a signal into the TV, and it displayed it just fine (just a noisy power supply to my ears)


The 2nd photo shows my diagnostics of the Power Supply.
Pin 13 labeled "PS-ON" has 0 volts in standby mode and 5v when the power button is pressed.
The voltage is persistent on this pin, however the "power" led only stays lit for about 5 seconds before fading out. After witch you can again power it on for a brief time.

I am not sure if the power supply quality is the underlying issue, or if there is a fault on the main logic board.
Can anyone suggest how I can test this?

Thanks!
 

inglewoodpete

Senior Member
Still not sure why this is in a PICAXE Completed Projects forum but....

Electrolytic capacitor values are often adjacent to the negative side stripe. In this case, it should be between the stripe and the circuit board.
 

srnet

Senior Member
Its already been suggeted over in the Arduino forums what you should do.

And the topic has nothing to do with Arduino either.
 

westaust55

Moderator
Maybe the TV’s and PICAXE are those used in this past thread:
http://www.picaxeforum.co.uk/showthread.php?29190-Adding-PWM-speed-control-to-Linear-Actuators-for-TV-control&p=301121#post301121

As for the Electro caps in the photo, you need to look at the hidden side of the caps for the uF and voltage ratings.

But unless there happens to be a TV repair wizz on this PICAXE microcontrollers forum, seems you would be better to post on a TV repair website. The connection to PICAXE based on the link above is very tenuous.
 

goom

Senior Member
Try re-flowing the solder joints in any area where you suspect a problem Worked for me once on a radio receiver.
 

PhilHornby

Senior Member
I am not sure if the power supply quality is the underlying issue, or if there is a fault on the main logic board.
Can anyone suggest how I can test this?
By substitution!

Have a look on eBay, and you might be able to obtain a second-hand replacement board.

I've just recently brought a Sony TV back to life by doing that. A lightning strike and brief power outage had left it with a slowly blinking RED light. The Sony's power board is huge and has hundreds of surface-mount components on the underneath. Just printing the circuit diagram in all its glory was causing me grief, so I took the easy way out and spent £26 on a replacement board.

If I ever have a spare month, when I can't think of anything else to do, I may have a go at fixing the original board ;)
 

1968neil

Senior Member
This is an obvious fault to an Ex-Tv Engineer :)
Electrolytic capacitors in LCD tv's dry out to the panels poor layout design, IE: electrolytic capacitors situated next to heatsinks that run hot !

I would suggest , working from the mains input of the panel replacing the electrolytic capacitors, usually the culprit for poor psu start will be a low value high voltage cap.
It may be worth checking ebay as some sellers provide a complete capacitor upgrade/refurb kit especially if the panel is made in Turkey (Vestel will be the manufacturer).
Hope this helps ?

I know that others have stated this is not a picaxe issue, however i feel that sort of comment is negative, the person asking the question may have enough interest if helped to try picaxe in the future !, especially when he/she realises that we are ALL a helpful bunch :)

Regards
Neil
 

erco

Senior Member

westaust55

Moderator
Likewise, a couple of years ago a DVD player at Home went through intermittent to failed.
I changed out all the electro capacitors on the circuit board and it is still working !
 

PhilHornby

Senior Member
Big board....lots of caps...

I successfully resurrected a Netgear switch, by changing the 3 or 4 electrolytics it contained...

...however, the O/P's PSU board looks as complicated as the Sony one I tackled. I counted 26 electrolytics, of various shapes and sizes.

Sourcing them, de-soldering the originals from their plated-through holes and installing the replacements didn't appeal to me at all. A replacement board was much quicker and easier - and I'll bet, not that much more expensive.
 

inglewoodpete

Senior Member
My experience is similar to many others who have posted here.

My Topfield (South Korean) PVR failed just a few months out of its warranty period. While Australia has warranty laws, it also has a "fit-for-purpose" law where a manufacturer is required to repair faults that are shown to occur both inside and outside that warranty period.

The PVR fault was in the power supply board and I would have had to send the whole PVR 3,000km to the east coast, at my expense, for diagnosis and repair. Being an electronics tech, I chose to simply do a full replacement of every low-ESR capacitor on the PS board. The PVR is still going fine 5+ years later.

I wonder if it has more to do with the quality of OEM low-ESR capacitors in Korea, highlighted by the heat generated in switch mode power supplies.
 

srnet

Senior Member
I know that others have stated this is not a picaxe issue, however i feel that sort of comment is negative, the person asking the question may have enough interest if helped to try picaxe in the future
Based on that there is no point in having forums based on particular subjects, if totally unrelated topics are considered acceptable.

Should for instance there be open discussion of problems related to other microcopntrollers systems on here, after all its possible that someone asking for advice on a particuilar microcontroller system, might consider Picaxe at some point in the future ?
 

premelec

Senior Member
i think discussion of failure modes of discrete components is fair... I've seen problems related to capacitors and resistors - took a while to figure out and trouble shooting methods being discussed help many of us to make a success eventually. I wouldn't extend this to other micros hardware which have their own special forums... unless related to peripherals which are used on a variety of micros including PICAXEs... Translation of code from one system to another also seems ok if it gets the PICAXE going....
 
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