[757labs] 37" TV, power supply troubleshooting

[Kyle Kroskey]

Caps. REPLACE THEM ALLL!!!!!!!

On Wed, Jun 22, 2011 at 1:37 AM, Mr. Grundy <geogrundy at gmail.com> wrote:

> Can u have a class or show me how to one of those?
>
> On Jun 22, 2011 1:27 AM, <telmnstr at 757.org> wrote:
>
>
> 37" TV.
>
> Has a switch mode power supply.
>
> Outputs are +24, +9, +5, +3.3 all DC of course.
>
> Symptoms: Plugged into wall standby blue LED comes on.
>
> Hit power, the back light flashes for a split second, LED also turns red.
> Then backlight cuts off. LED goes blue. Then later it goes through the
> process over and over.
>
> Troubleshooting:
>
> First thought was, it's the backlight inverter board. Dug into it, looked
> fine. It kind of dawns on you that it's a complex board a little later. I
> did a proceedure to check to see if any of the back light transformers were
> open, but all were fine. Looks good.
>
> Had the idea to isolate the board, unplugged it from power supply, same
> symptoms.
>
> Did the same thing with the CPU board, nothing really eventful.
>
> Busted out the oscope.
>
> Turns out +3.3vdc line is stable all the time. Always. It's what is
> powering the standby.
>
> All the other voltages, when the TV cuts on all voltages drop. The power
> supply is being pulled down.
>
> So I unhooked everything, and crossed the +3.3vdc line to the "power on"
> signal wire on the supply. It retries over and over much quicker, but this
> could be normal since there isn't a load on it.
>
> Gonna poke at it more tomorrow. Kind of an odd one, because it's difficult
> to nail down which actual board is causing the issue.
>
>
>
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> If we knew what we were doing it wouldn't be research.
>
>
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> If we knew what we were doing it wouldn't be research.
>



-- 
Thanks,
Kyle Kroskey
solareon at gmail.com
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