Lexsor 32" LCD (Model Unknown) w/ 24V bus measuring 1.4 - 1.8V

[Greeno]

Re: Lexsor 32" LCD (Model Unknown) w/ 24V bus measuring 1.4 - 1.8V

Hi

I've had one of these sets sitting around for a while (too long), having decided that it probably wasn't worth fixing but unable to bring myself to throw it out. I had previously replaced all the capacitors on the power board so I've decided to have another look at it.

Sometimes the backlight comes on and other times not. When it does come on, the menu and input selectors will display but the screen becomes increasingly corrupted and eventually goes solid blue.

When the backlight doesn't come on, N705 is not being switched on (pin 5 is 5V); when the backlight DOES come on, it IS switched on (0V at pin 5) and I measure 5v at the output. Same for N704 - 5v output appears good (no switching).

My question is, does reading 5v at the output of these converters mean they are OK?

Thanks.

[tom66]

Re: Lexsor 32" LCD (Model Unknown) w/ 24V bus measuring 1.4 - 1.8V

Yeah they are supposed to be 5V output. Could be some bad caps on the output of thosse converters.

[Greeno]

Re: Lexsor 32" LCD (Model Unknown) w/ 24V bus measuring 1.4 - 1.8V

So...I have now replaced the 4 large electrolytics associated with the N704 and N705 and the television is better (stable) but still not fixed. I have attached a couple of pictures of the screen with no input and with the menu displayed, which shows the spurious, stationary pixels. With an input, these change to a few vertical lines.

There are couple of surface mount electrolytics in this circuit (22uf 16v) which I have not replaced due to the difficulty in removing them - could these be causing this problem (more probable than the ceramics, I thought?) or is it more likely the fault is now elsewhere?

Thanks for your assistance.


.

[tom66]

Re: Lexsor 32" LCD (Model Unknown) w/ 24V bus measuring 1.4 - 1.8V

Have you yet measured the output of those converters?

[Greeno]

Re: Lexsor 32" LCD (Model Unknown) w/ 24V bus measuring 1.4 - 1.8V

If you mean N704 and N705, yes, they were 5 volts perviously and they are still 5 volts.

[update: I decided to remove the aforementioned SMD electrolytics - replacing them with some through-hole caps I had, thinking they would be OK - and it seems to have made it worse.]

[notallbad]

Re: Lexsor 32" LCD (Model Unknown) w/ 24V bus measuring 1.4 - 1.8V

I have an unknown Lexsor, 32" I think, with a broken screen. The tv powers up and does still work!
If it would help I shall dig out the tv and check if the PS b/d happens to be the same as yours.
Are there any voltages you would like checked to cross reference, or any components that I can check to compare to yours? Or other measurements?


It is a 32" but PS B/d : L32W19-20