HH251 Humming and backlight issues

[Flashgun]

Introduction
Hi guys,
this is my first thread but you already helped me fixing other displays quite a few times, so I'll take this chance to thank you!
That being said, let's get to the issue:
The Culprit
A 3 years old 24.6" Hanns-g HH251HPB.
Symptoms

1. A couple months ago it had the 5-seconds-to-black issue, but after opening it up to take some reading it began working again by itself but with a "silent" high frequency humming when turned on.
2. A couple days ago it became very dim and the brightness control had no effect (I tried setting both 0 and 100 and noticed no difference), the high pitched noise became louder even with the monitor turned off (as soon as I plugged the cord in) and I noticed that the right side was slightly brighter than the left side.
3. Today it went in 1-second-to-black mode.

Testing

• No evident burning or bloating.
• I checked the diodes and fuses and found no issue.
• I checked with a spare working CCFL with no luck (I guess all CCFLs are working)
• don't know if I got the reading wrong, but I found three transistor with some strange reading (circled red in the front photo)
  -Pin 1,2 and 2,3 show >20 Ohm
  -Pin 1,3 showed 0,4 Ohm
  At first I tought it was a short, but since I got the same reading on all 3 of them it seems like a strange coincidence, am I missing something?
• I narrowed the source of the humming from somewhere in the black circle in the front photo (the component with yellow tape is some kind of transformer, right?)

Conclusion
I tried searching the web for some solution but I found nothing, is there anything else I can do (beside trying to change the inverters) or test?
Thanks again for the help!

[nutt318]

Re: HH251 Humming and backlight issues

Did you ever get this monitor fixed?

I've got the same issue, it displays for around 1-2 seconds then goes black. Also it has a little high pitch sound while plugged in.

Also If i take a flash light and shine it at the screen I can see the image. Does that mean the back light is bad?

[selldoor]

Re: HH251 Humming and backlight issues

Did you ever get this monitor fixed?

I've got the same issue, it displays for around 1-2 seconds then goes black. Also it has a little high pitch sound while plugged in.

Also If i take a flash light and shine it at the screen I can see the image. Does that mean the back light is bad?

Could be the back lights or the inverter transformers - see here
https://www.badcaps.net/forum/showthread.php?t=10419 start at post19

[nutt318]

Re: HH251 Humming and backlight issues

Thanks selldoor, I'll start working through the guide.

[selldoor]

Re: HH251 Humming and backlight issues

If you get stuck or dont understand just ask.

The inverter transformers are a little unusual - hope they are ok
I THINK the secondary winding posts are as in the pic.
No power to monitor meter on ohms 2000 test s1 to s2 and s3 to s4
and post the results.

[nutt318]

Re: HH251 Humming and backlight issues

Hi Selldoor,

The back of my board appears to be a little different, would you mind pointing out the test locations?

Back:
http://imgur.com/O2WffHZ

Front:
http://imgur.com/4oc8mDG

Also I test all capacitors and some dont change at all on the multimeter and others will display 150ish,then 130ish, then 100ish and the to 1 or -1. Does this mean that all the capacitors are bad?

Thank you!

[selldoor]

Re: HH251 Humming and backlight issues

OK we prefer pictures to be posted with " Manage Attachements" you would need to resize to 2mb - Off site ones dissappear then the thread makes no sense.
You will need to scrape off/peel back the white insulation.

You cant really test capacitors with a multimeter - wouldnt worry about them for now.

[nutt318]

Re: HH251 Humming and backlight issues

Sorry about that, I'll make sure to attach them next time.

I'll post results later tonight when I get home. However I did test test the 3 transistors last night. All 3 acting the same as below shows.

Pin 1 & 2 - would flash a number between 100 and 150 and then go to 1 or -1
Pin 1 & 3 - 0.8ohms
Pin 2 & 3 - would flash a number between 100 and 150 and then go to 1 or -1

Thanks

[nutt318]

Re: HH251 Humming and backlight issues

I've just tested both sets of areas and my multimeter didnt change any. It just stayed on 1 on the left side of the screen.

I was testing them on 200ohms.

Thanks

[Rtech]

Re: HH251 Humming and backlight issues

If the 'areas' you tested referred to the transformers ,as pointed out by Selldoor, then the range of your meter needs to be set higher than 200Ω.

[nutt318]

Re: HH251 Humming and backlight issues

What setting should I test it with, how many ohms?

[selldoor]

Re: HH251 Humming and backlight issues

2000 ohms as per post 5?