1-second to black 22" LCD need guidance

[stormy1777]

Hi friends..

The question up-front:

Is it safe/OK to replace a ceramic capacitor marked "5J 3KV" (which I assume is a 5pF, with a 10J 3KV, which i assume is 10pF.. I know the general rule in Electrolytic capacitors that one can go higher on the Voltage, but not on the capacitance.. Wondering if that minor (double) change will result is some "hazard" when ceramic capacitor and high voltage is at play ?


I've carefully reviewed this guide over past few days:

https://www.badcaps.net/forum/showthread.php?t=10419

this LCD TV display powers on the LCD for split second, then turns off. I've attempted many tests but need some guidance..

1) The main board seems OK, disconnecting the driver (HV) board shows that it is consuming ~12W and delivers 12VDC on the wires going to the driver board.

2) the backlights are all OK, tested with a dedicated external LCD/CCFL driver, and all 4 lights turn on, and stay solid for long time.

3) Also tested with external, known to be good CCFL (see image), and we get a burst of light (power goes up to ~30-40W for that split second), then they go OFF...

4) Originally, there were two 25V@220uF Electrolytic capacitors which APPEAR to be leaking, but i think it's just some GLUE. they test OK on ESR meter as well as dedicated capacitor meter. Anyways, replaced with 50V220uF since it had the SAME physical size, and the new 25V220uF I had were HALF the size, so decided it is safer to go with the 50V.. Same effect after replacing both of these.

5) Before I venture into totally unknown territories (like these scary "inverters"), spotted two blue ceramic capacitors marked "5J 3KV", took them off circuit, one gave 4.6pF, other 5.4pF. Now I realize that is not telling much, esp. due to low values, but then I do not have a 5pF, wondering if it is safe/OK to replace with 10pF which is the closest I got on hand


Otherwise, appreciate any other ideas on how to diagnose this issue... or maybe the only recourse is replace the whole driver/inverter board....?


Thanks in advance,

Stormy.

[Andrew F. Ali]

Re: 1-second to black 22" LCD need guidance

If you have 2 of the 10pF caps you can make a 5pF cap by connecting the 2-10pF caps in series to produce a 5pF cap.

[budm]

Re: 1-second to black 22" LCD need guidance

1) So did you replace those two lytics caps on the inverter board with low ESR type caps?
2) 5J = 5pF, 10J = 10pF if they are bad they will show leakage resistance when tested with Ohm meter.
3) Did you test the resistance of the High Voltage winding side of the inverter transformers?
4) Did you verify that the Voltage feeding the inverter board (12 ~18VDC is typical) and the Control Voltages (BL-ON, DIM) stay present when the lights go off?

[stormy1777]

Re: 1-second to black 22" LCD need guidance

1) Yes, as shown, and explained in #4 they were replaced, with same effect of black after ~1sec.

2) Based on reading such places: http://www.facstaff.bucknell.edu/esa...captester.html, understood that a DMM cannot find such leaks of high voltage, and i do not want to touch the board when it is fully energized... not sure how to test. DMM shows OL when sent in Ohm mode, so i think that is OK.

3) no clue how to do that...

4) have not, will do that shortly.

For now, I'm tempted to go with the suggestion to string 2 10pF and see how that works out...

Thanks for the support.

Stormy.

[dick_barton]

Re: 1-second to black 22" LCD need guidance

What is the part number of U1 on the inverter board? Is the set still working when the baclights go off ie can you hear the sound and see a picture on the screen if you you a bright light and angle it?

[stormy1777]

Re: 1-second to black 22" LCD need guidance

Update:

1) replaced both 5pF with couple of 10pF, as shown in photos, however, same black screen comes...

2) After black screen, the voltage on the ribbon that feeds the inverter board shows 12V (red to black) and 5VDC (red to white) (maybe that is similar to what was asked "BL-ON, DIM"?.. so I'm thinking it is something with that inverter board..

3) could not get the part# of U1, will need to go out to sun maybe with better quality light...

4) I don't have any TV signal to feed it, nor do i know if the speakers ever worked, it is used as a PC monitor, just the vision part. Did not manage to "see" with a small flashlight, i'll need to find a strong light source to attempt to see if screen is visible or not.. there is a GREEN light and that is ON (when monitor is OFF, the light iis RED).

5) is there any "easy & manual method" to "drive the inverter board? it sounds like if one could provide the 12V+5V on the right wires, that board would not be able to tell the difference, and will just power on the monitor (assuming it is not defective)..

otherwise not sure what else is within my scope/abilities to repair

I've replaced all 4 capacitors on that driver board...not sure what else to try...

Stormy.

[budm]

Re: 1-second to black 22" LCD need guidance

https://www.badcaps.net/forum/attach...4&d=1538599623
Von/off = BL-ON (typ. >2.5VDC = ON) Ref. to GND (Blak wire).
Vbrit = Diming control, it may be DC 0 ~5VDC (5V = full brightness) or PWM type control signal, ref. to GND (Black wire).

[stormy1777]

Re: 1-second to black 22" LCD need guidance

OHH regarding the "vbrit/von/off/vcc" I think got it!! That maps to the 6 wires that drive the inverter board. OK, so, Tested again, here are some findings:

1) Results are same when display is OFF (but energized, connected to power) and right AFTER the screen goes black, in both cases these are the numbers in relations to GND (black):

vbrit 0VDC
von/voff 90mV
vcc 12.3VDC

Maybe something is wrong with the "vbrit" ? or maybe von/voff is too low?? or both? funny almost sure i saw 5vdc the other day somewhere there, but cannot find it now.

so maybe something on the MAIN board needs replacing? I'm all for replacing bad caps, just no clue which one there are so many and none look bad or burnt in any way

I'll checked in-circuit (using ESR meter) many of the large caps, they appear OK...

2) As for this:

3) Did you test the resistance of the High Voltage winding side of the inverter transformers?

I'm not sure how to test these beasts, they have 2 pins on one side, and 6 on the other.

Here is what I did with DMM:

2.1) Ohm meter, all 6 pins on each of the inverters all show up as "0ohm", so all are same point it seems?

2.2) from any of the two pins to any of the other 6 pins within the same inverter, the reading is "OL" - so , no contact...

2.3) Ohm reading between the two pins, in both inverters comes as: 0.93KOhm.

Appreciate any leads on where to go/spend time next

Thanks!!

Stormy.

[budm]

Re: 1-second to black 22" LCD need guidance

Are the test done with the unit connected to running PC or with Video source connected?
It looks like the main board just stops sending the two needed command signals (BL-ON and Dim).

[stormy1777]

Re: 1-second to black 22" LCD need guidance

just power, no video source.. I'm suspecting i would need to connect to some PC/laptop... ok, let me see if that changes anything, although it behaved in same way when it was on the PC, i.e. fade to black.. and the TIME seems to reduce, i.e. now it is less than 1 sec fade to black

[stormy1777]

Re: 1-second to black 22" LCD need guidance

Noticed it changed behavior a bit with the two 10pF capacitors, maybe connection was not great, after POWER off, the GREEN light would not stay, it turned to RED light, i.e. completely OFF, power consumption dropped to 2-3W..

so, put the original 5pF capacitors, and now after power off and GREEN light remains ON, with ~12W power draw, and the voltage values to inverter board are now (after screen is black, light is GREEN):

vbrit 0VDC
von/voff 4.8VDC
vcc 12.3VDC

these values appeared with or without Video Source (there is AV/TV button, so kept pressing it, but it did not seem to change anything).

I'll test/compare more thoroughly the bunch of capacitors, marked CD11C and CD263, found on main board...
Stormy.

[stormy1777]

Re: 1-second to black 22" LCD need guidance

Well, scanned the main board, could not find anything glaring, all diodes look clean, and low ESR.. then remembered some LED debug kit got while ago, in it was a small "driver board", connected it and:

1) it did not power the CCFL on the monitor, i think that is expected, those require HV..

2) it did deliver 12VDC on the output ports, put LED strips and it did power them up.. so , maybe the inverter board is bad after all...

I might order something and see

Thanks for the help.
Stormy.

[stormy1777]

Re: 1-second to black 22" LCD need guidance

sorry, here is the photo prior session timed out and did not upload the image.

[stormy1777]

Re: 1-second to black 22" LCD need guidance

Here is an update, with new photos.

Got a replacement Video inverter board in the mail, it looks good, and identical to original one, installed the new one, and same thing, 1-sec and it goes to BLACK (it does manage to print the LCD logo)...

Took a separate interter device, and all 4 CCFL harnesses produced bright light on the display, so i was driving each one separately, and they all turned on and stayed on for long time.. which means the lights are OK, the inverter board is probably OK, which leaves the main circuit board...

that one is rather large with many smaller capacitors, I have no clue which would cause this issue... and to replace them all, well, I'm not really set up for that...

was thinking to order a replacement board: M220EW01 from ebay and try my luck a second time, only thing is all these look much NEWER compared to this one, so might need to make some adjustments once it arrives..

anyways, just though to drop this update and possibly there will be another update at a later time..

Stormy.

[stormy1777]

Re: 1-second to black 22" LCD need guidance

Happy ending to this thread... ended up ordering a really cheap KIT from "China", it is totally different even though seller promised it is the same model to the letter.

In any event, as you can see, nothing aside from the monitor ribbon/cable fit, different sizes plugs, etc. so speakers and controls are not working, but it's fine, there are external speakers anyways.. power is on front panel

Thanks for the help, it ended up being the main board that was defective!!!

Stormy.