Hanns-G HH251 no power

[maudam]

Hi all,

i have a dead hanns-g HH251 25" lcd display.

During last months, the display suddenly power off and on again after some seconds with any apparent cause.

In a couple of cases this power off went on for some minutes.

Now the display won't power up.

With some tests, i found the same problem at this thread but i'm not sure that only the fuse is broken.
https://www.badcaps.net/forum/showthread.php?t=22967

The smd fuse F102 (Marked with Y letter) seems broken, but i wasn't able to find this fuse or any oher info at any place.

The board output should be:

5,2V 3.1 A
12V 0.7 A

so the 5.2 line protected by F102 should be 3.1A but the same fuse is on F101 that should be a 12v 0.7A

12V line is not active. Maybe the monitor have to power up before 12v are activated ?

All the caps seems good. No leaks at any place.


Please help me troubleshoot.


Images on thread https://www.badcaps.net/forum/showthread.php?t=22967 are equal to my board so i'm not reposting.
If you need i can post other pictures.

[selldoor]

Re: Hanns-G HH251 no power

I really dont think you can expect us to waste our time switching between threads to look at boards which are not yours.

Suggest you try it with a 5a 12v fuse, but as long as the voltage is above what it needs to carry it is ok for a test, until you find out what it should be. Members generally solder in a pico fuse as they are easier to come by but you could wire in an automotive fuse if you are careful to solder it well and keep it well insulated.

Also a fuse cant "seem" to be broken it either is or it isnt

[maudam]

Re: Hanns-G HH251 no power

Hi selldoor,
thanks for your answer and sorry for the pictures.
About the fuse, do you think a 250V 3A fuse is good for test or i risk to burn all ?

[selldoor]

Re: Hanns-G HH251 no power

If you have nothing else it would do for a test - at 3A it is a bit low and likely to blow but
should not damage anything else - If it is a glass one shield it when you first try and do not
look at it, just in case it explodes.

[Davi.p]

Re: Hanns-G HH251 no power

If the board says "12V 0.7 A" why to put a 5 or 3 Amp? For me is enough 1A.

[maudam]

Re: Hanns-G HH251 no power

davi it is for 5.2V 3.1A.

I'm going to try it.

[maudam]

Re: Hanns-G HH251 no power

I have just tried.
The fuse is bypassed with the external fuse 250V 3a but the monitor won't power on.

[Davi.p]

Re: Hanns-G HH251 no power

It was better if the picture was more closer to the interesting part, we cannot see where you have placed wires.. apart this if you now are able to see 5v on the output connector the next step is to control the voltage regulators on mainboard.

[selldoor]

Re: Hanns-G HH251 no power

OK - doesnt power on can mean a lot of things.

Can you test the voltage across the BIG cap It will be HIGH voltage so careful.
Put your meter on 600vDC and place a probe on each leg of the capacitor.

[maudam]

Re: Hanns-G HH251 no power

Well.

290V on C100 (bigger cap)
29V on C203 (near transformers)
0V on C105 (brown cap just up to external connector)
No 12v on pin 10 of external connector
5v ok on pins for external connector
Fuse F100 ok

Davi can you tell me which are voltage regulators and how check them ?

[selldoor]

Re: Hanns-G HH251 no power

Does the screen flash at all?

[maudam]

Re: Hanns-G HH251 no power

Nothing. Completely off as the power led.

[selldoor]

Re: Hanns-G HH251 no power

Ok - Still not sure how you have connected the fuse are you getting 5 v on both sides of it. Which pin is connected to C105?

The voltage regulators are on the main board if you can post a good clear picture of it.

[Davi.p]

Re: Hanns-G HH251 no power

I think 12v rail must be always present, from what i can see, because OUTPUT connector (not external) has too few contacts for a control pin, so you need to check voltage on central pin of all the three legs diodes on heatsinks and if you don't find 12v switch off and test with diode tester that diode.

[maudam]

Re: Hanns-G HH251 no power

For the fuse, i made a bridge on pin 5 of external connector, that is directly connected with pins 4 and 6 and one side of broken F102, and JP104 that is directly connected to the other side of broken F102.
In attached pictures you can see more details.

[maudam]

Re: Hanns-G HH251 no power

davi, i'm going to do it now

[maudam]

Re: Hanns-G HH251 no power

All transistor in picture marked with yellow circle is ~20V on central pin.
Transistor with circle red and yellow is 0V on central pin.
By the way, external connector have some pins marked:

brt
inv_on
ps_on

Could be a control pin for 12v ?

[maudam]

Re: Hanns-G HH251 no power

Transistor readings

[selldoor]

Re: Hanns-G HH251 no power

Ok what you could try is disconnect the main board and with a 1k or .5k resistor
connect the 5v pin to the InvOn and see of the back light stay on.
I think brt is the same as dim so you may need to bridge that also using a resistor.
If there is voltage at that cap between the inverter transformers there should be power there and it may only need a signal to switch them on.

[Davi.p]

Re: Hanns-G HH251 no power

Your last pics are much nicer and i can see better, your psu is probably OK, PS_ON is a return signal from ma.bo. and need to hook it to get 12v to work. We need a picture of the main board so we can mark where to measure.