Cibox LW1922C dead, no power

[diif]

Whilst i continue my search for main board for another monitor i own i thought I'd try another monitor i have sitting on my shelf.

It's a Cibox 1922C with no signs of life. LED doesn't light, no flicker from the back light.

I've removed and tested several components, fuse, bridge rectifier, mosfet to the right , big cap and the 3 to the left of the heat sink.

If someone could give me some pointers and advice as to what to check next that would be greatly appreciated.

thanks

[budm]

Re: Cibox LW1922C dead, no power

OK, start by running the power supply-inverter board combo by itself, no connection to the logic/scaler board. Read the Basic LCD monitor troubleshooting guide.
Measure the DC voltage right AT THE TWO LEGS OF THE MAIN 450VDC filter cap and report the reading.

[diif]

Re: Cibox LW1922C dead, no power

Thanks for the reply.

It's 342.4v

[selldoor]

Re: Cibox LW1922C dead, no power

That is Ok can you test the voltages on the connector to the main . There wont be many perhaps just on the 5v pins so meter on 20vdc use a ground screw or ground pin on the connector.

[Phoenix83]

Re: Cibox LW1922C dead, no power

On that black conn. on the 1st image, measure pins 1, 5, 8, 10 to the GND.

note: do it with logical board connected

[selldoor]

Re: Cibox LW1922C dead, no power

I have not seen this board before - any ideas what the 3 switches are for? cant say Ive seen a board with switches before!!

[diif]

Re: Cibox LW1922C dead, no power

There are a couple that say VCC5V but they are both fluctuating between 2.5v and 2.7v.

[budm]

Re: Cibox LW1922C dead, no power

I would test those DC voltages on the black connector without having the main board attached since the main board can have shorted circuit that caused the power board to be in shut down mode. Since voltage is fluctuating, I would suspect bad start up cap. Try heating it with hair dryer or replace it.

[diif]

Re: Cibox LW1922C dead, no power

Nothing showing on 1 and 5 fluctuating between 2.5 and 2.7v on 8 and 10.

The buttons are for power and making selections in the menu.

[budm]

Re: Cibox LW1922C dead, no power

1 and 5 and other voltages will not be correct until the 5V is corrected first.

[diif]

Re: Cibox LW1922C dead, no power

Cheers for the help, i shall purchase some caps tomorrow and replace and let you know how i get on.

[selldoor]

Re: Cibox LW1922C dead, no power

Any caps will not do the job you need to buy low esr ones for this application.
We usually recommend Panasonic FR FM or FC remember to check you have room as they come in different sizes - sometimes for the same value.
I dont know big suppliers in the midlands perhaps RS electronics have a trade counter? Dont try anything from Maplins. cpc have a delivery free on all orders
offer.
Often next day delivery though probably too late for tonight.

[diif]

Re: Cibox LW1922C dead, no power

I've removed the Su'scon cap. it's 47uF 25v, tested on my ESR it gives a reading of 47.84uF and and ESR of 0.84 ohms but his doesn't seem too high ?

RS is only a 20 minute drive away.

[diif]

Re: Cibox LW1922C dead, no power

I replaced the cap with a KY low esr, with a value of 0.4 ohms and the 5v has come up to near 3v now instead of the 2.5 to 2.7v although it still fluctuates but only by about 1v

I have noticed on the other side of the board an 8 pin chip marked 203D6. It's referenced in another post and leads to this data sheet, some sort of power supply ?

https://cdn.badcaps-static.com/pdfs/...93618ef001.pdf

Is it possible this is at fault ?

[selldoor]

Re: Cibox LW1922C dead, no power

Possibly but I dont know how to test - Budm will. If he doesnt come onto the
thread I will try and look it up tomorrow.

Is that 3v with the main board and lights connected? have you tried with
just the power supply board. Also just to check you are testing on pins 10 and 4 or 10 and a ground screw?

[budm]

Re: Cibox LW1922C dead, no power

I would test those DC voltages on the black connector without having the main board attached since the main board can have shorted circuit that caused the power board to be in shut down mode. Since voltage is fluctuating, I would suspect bad start up cap. Try heating it with hair dryer or replace it.

Is that how you test the voltage? Details, Details, Details always help.

[diif]

Re: Cibox LW1922C dead, no power

Today i have resoldered the mosfet as i was a little unsure of my original soldering. I get about 4v now (tested with nothing connected).

Now when i connect the mainboard and lamps the power led glows a dim flickering orange that stays on for a few seconds before going out then coming on a second later. the longer the power is left plugged in the shorter the time the led stays lit.

Measuring the 5v with everything plugged in i get about 1.7v but it is fluctuating. Ground screw and pin 4.

I am off work tomorrow and can get to RS to buy anything needed.

[selldoor]

Re: Cibox LW1922C dead, no power

Are you testing pin 10 to pin 4 ?
Where did you get that KY cap what voltage do you get across it - is it steady.
What make is it
( using power supply only no lights& no main)
Retest the BIG Cap was the voltage on that steady over 10 seconds.
If you dont have any, pick up two 1kohm resistors.

[diif]

Re: Cibox LW1922C dead, no power

Yes pin 10 to pin 4. The cap came from an ebay seller that sells low esr caps for electronics repair.
It is marked KY which i understand to be Nippon Chemi-Con Corporation. Is it possible they are not what they claim they are ? They have an esr of 0.4 according to my meter.

The voltage across the cap is not steady it seems to go in a cycle 10v to 6v then goes back to 10v

The voltage on the big cap is showing between 337v and 340v but it's not fluctuating as wildly as the small start up cap.

Thanks for your help.

[budm]

Re: Cibox LW1922C dead, no power

OK, it sounds like the power supply is in start up-shutdown mode, we will have to disconnect the power to the inverter circuit to see if it will become steady.
I will have to trace out the connections on the bottom side of the board to see what you have to disconnect.