SHARP LC-42sb45u powering on and off

[capcom]

This set is a black friday special (go figure its giving me problems)
A few days ago it started turning itself on and off, I would reset the cable box and it would be fine that night. Then I would wake up to hear the TV on. I took the back panel off and everything looks good. Next step is buying a meter to test some caps. I know this is a common problem, I'll try and get some hi-res pics up today because I have no idea what i'm looking for except obvious bulging caps. All the caps in this thing are capXom. Thanks for looking!

[mmartell]

Re: SHARP LC-42sb45u powering on and off

This past Black Friday ? You took the back of a brand new tv that's under warranty ?

[capcom]

Re: SHARP LC-42sb45u powering on and off

No no from 3 yrs ago. :-/

[mmartell]

Re: SHARP LC-42sb45u powering on and off

Haha that's better then...

Maybe a cold solder joint causing intermittent connection as well.

[capcom]

Re: SHARP LC-42sb45u powering on and off

Heres some hi res pics.

[capcom]

Re: SHARP LC-42sb45u powering on and off

what are the blue markings on the PCB? Is HQ902 an obvious Cold Solder Joint?

[capcom]

Re: SHARP LC-42sb45u powering on and off

I finally bought a MM and I tested the 4 big caps out of circuit and they are all reading at their stated values. Did some testing on the pins and the 5v standby by is reading 4.48v when the set if off, and 5.19v when set is on. The two blue wires which are 12v are reading 12.25v when on.

Most of the caps on this psu are capxon, thinking about changing atleast the 4 bigger one.

I read through this thread: https://www.badcaps.net/forum/showthread.php?t=18894

My standby voltage is the same >5v , Since this set is powering on and runs for a period of time before turning itself on/off, i'm not sure if all the testing done in that thread apply to me. Thanks for any insight.

[capcom]

Re: SHARP LC-42sb45u powering on and off

I just got back from a local electronics store and picked up some caps to replace the 4 bigger caps. This is the best I could do for a fit because of the very limited stock there.

C952 : CapXon 680uf 50v replacing with NTE 1000uf 50v
C951 : CapXon 680uf 50v replacing with NTE 1000uf 50v
C956 : CapXon 1000uf 25v replacing with Jackcon 1000uf 25v
C955 : CapXon 2700uf 16v replacing with Jackcon 3300uf 16v

Odd thing to me is that The Service Manual shows caps that are different than what are actually on the board. I'm a total newbie to this, so I dont know if this is common but heres a screen shot.

[capcom]

Re: SHARP LC-42sb45u powering on and off

Ok, so I just did more research and realized there needs to be more effort put in to finding replacement caps. Turns out all the caps I bought are General Purpose, and I need to match the impedance,ripple and uf to a T if I can. Luckily I'm only out $7.50.

Can someone suggest if I should match the replacement caps with the ones that were taken off the board or with the values shown on the Power Schematic?

[capcom]

Re: SHARP LC-42sb45u powering on and off

I replaced 5 caps and I think I may have fixed the powering on and off problem. But now the Tv menu keeps flashing on and off by itself. Has anyone head of such a thing?

thanksyou in advance

[f67bird]

Re: SHARP LC-42sb45u powering on and off

The board with the switches (power, volume, channel, menu) can be unplugged, letting you control the tv with the remote. Try unplugging that board and see if the menu still comes up on its own. If the menu now does not come up on its own, one of the switches is leaky or bad.
If the menu still does come up by itself, the main board is most likely bad... double check all power supply voltages to the main board just to be sure they are correct. Also you can check sharps website to see if there is firmware for this model that addresses this issue.