Hannspree HF237

[ixtlan]

What a forum this is.
Great info and experience abounds!

Sorry for the length of this post but I did want to provide details.

Well that said I have a problem with a Hannspree HF237 monitor.
I have replaced the caps and still seems to have an issue with 2 seconds on and blank,
Power led stays lit.
I have read about the 2 second problem and using a flashlight to see if the backlights are off.
Dont really understand how to do this to be honest.
Do I shine the FL into the screen and see if I can see the image?
Or do I need to get behind the screen?
From the front I see nothing fyi.
That newb question asked.
I have replaced the caps and still have the problem.
Nothing visually appears damaged or otherwise unusual on the board.
It will run for hours and then when the power is cycled (reboot or via power switch) it may not come on except for a brief time or not at all.
If left on it may start working. And may not.
If it does it will be 5 minutes before it does then it goes blank after a few seconds again.
It started initially with taking longer and longer to come up.
This progressed to what it does now.


At a loss to where to look now.

Thanks for any brainstorming offered.
And again apologies for the long post.

[PlainBill]

Re: Hannspree HF237

What a forum this is.
Great info and experience abounds!

Sorry for the length of this post but I did want to provide details.

Well that said I have a problem with a Hannspree HF237 monitor.
I have replaced the caps and still seems to have an issue with 2 seconds on and blank,
Power led stays lit.
I have read about the 2 second problem and using a flashlight to see if the backlights are off.
Dont really understand how to do this to be honest.
Do I shine the FL into the screen and see if I can see the image?
Or do I need to get behind the screen?
From the front I see nothing fyi.
That newb question asked.
I have replaced the caps and still have the problem.
Nothing visually appears damaged or otherwise unusual on the board.
It will run for hours and then when the power is cycled (reboot or via power switch) it may not come on except for a brief time or not at all.
If left on it may start working. And may not.
If it does it will be 5 minutes before it does then it goes blank after a few seconds again.
It started initially with taking longer and longer to come up.
This progressed to what it does now.


At a loss to where to look now.

Thanks for any brainstorming offered.
And again apologies for the long post.

Better a longer post than one with little useful information. (We just love the "I have a monitor itson't work rite tellm e howe to fixit." posts - I just ignore them. Still, you faile to provide a couple of vital pieces of information.

I've had very little success with using a flashlight. The idea is to hold it at an angle and verify you can see an image on the screen.

The symptoms are contradictory. A monitor taking longer and longer to come up typically is caused by bad caps. What brand and series did you use? * At the same time, the behavior of the CCFLs sounds like they may be nearing their end of life. when they first turn on, is there a pinkish tinge to the picture?

Another thing to check is the resistance of the inverter transformer secondaries. A low resistance can indicate shorted turns.

It's been said, many times, many ways. No , not 'Merry Christmas', but 'Please provide pictures.* One, an over-all view of the internal parts of the monitor showing everything together, then pictures of the top and bottom of the power supply. Please attach them using 'Manage Attachments' - below the text entry area.

PlainBill

* = The two things you neglected to provide.

[ixtlan]

Re: Hannspree HF237

Ok the flashlight explanation helps.
But I can see nothing at angle or otherwise.
Next is the Caps.
Replaced them with Panasonic, Nichicon or Rubycon I purchased as a kit from a reputable supplier who actually refereed me here for further advise.
When the LCD does turn on it is instantaneous.
No noticeable pink or otherwise.
I will need to check the inverter resistances and get back with you.
Here is a pic of the board.
I will need to disassemble again to get better ones.
I want to review the How To for pics also.

[jsog]

Re: Hannspree HF237

Did you replace the small cap in the center of the board also?

[ixtlan]

Re: Hannspree HF237

Did you replace the small cap in the center of the board also?

As a matter fact no I did not.
I overlooked it completely
50v 10uF brand is Su'scon.

Is that brand a suspect one possibly?

[PlainBill]

Re: Hannspree HF237

As a matter fact no I did not.
I overlooked it completely
50v 10uF brand is Su'scon.

Is that brand a suspect one possibly?

Su'scon is a suspect brand - I would say 'replace on sight'. That cap performs a vital function. It's the start-up cap. When it fails the power supply won't start. Of course, it's so small that it doesn't have a vent, so a failure is invisible. And it's inexpensive to replace - under $.50, so I usually replace it unless it is a high reliability brand.

I recently had a very frustrating experience with a power brick for a 17" LCD TV. The TV would try to turn on, but fail. When the power brick was tested with an external 2A load it worked flawlessly. After substituting another supply for the power brick, the TV worked perfectly. Opening the power brick revealed three 'tier 2' brand (not as good as Panasonic or Rubycon, not as bad as Capxon of Elite) caps whose ESR was borderline high. Replacing them did not fix the problem. The startup cap was buried under a mass of glue. After replacing it, the TV worked perfectly.

PlainBill

[jsog]

Re: Hannspree HF237

SUSpect Capacitor Often Nonfunctional ?

Those little caps do sometimes bulge. FPD1765s have a 220uf 16v 6.3x11.2mm on the processor board that makes a nice little hemisphere dome. Can't recall the brand, might be Sus'con. Didn't save any of them.

[ixtlan]

Re: Hannspree HF237

I will see if I can find one local and swap it out.
Will let you know the outcome.
Little bugger slipped by me.
Goin blind I guess.

Thanks for pointing it out.

[PlainBill]

Re: Hannspree HF237

I will see if I can find one local and swap it out.
Will let you know the outcome.
Little bugger slipped by me.
Goin blind I guess.

Thanks for pointing it out.

The first time I encountered a bad start-up cap, I saw it, but focused on the obviously bulging output caps. Imagine my consternation when the monitor STILL wouldn't work. Imagine the hours lost until I found the answer here. (Thanks, Mike.)

PlainBill

[ixtlan]

Re: Hannspree HF237

Found a cap at the local Radio Shack.
It is an axial type and not marked + or - though.
One lead was wrapped around the cap.
The only markings are 10uF 50 v the brandname nichicon and a series of B P across the body.
Is this a non polarized?
Will it matter what is pos and neg?
How do I tell and can it be used?

[jsog]

Re: Hannspree HF237

I would not use that one. Radio Shack is the wrong place to go, an electronic supply house is better. Or Digikey, if you're able to wait a few days: http://search.digikey.com/scripts/Dk...name=P10316-ND

[ixtlan]

Re: Hannspree HF237

It is a recommended brand so I am not concerned with that so much.
Even though it did come from RS.
But can I use a non polarized cap in a polarized position?
Or if it is a polarized cap, how do I tell what is pos and neg?

[jsog]

Re: Hannspree HF237

Nichicon is a good brand, but they make different series of caps for different jobs. That one is a non-polarized capacitor meant for audio filtering, the wrong type, size, and maybe 85 degree instead of 105 degree. You'd have to bend one lead around and under, insulate it to keep it from shorting to the can, and then worry about whether the cap is too large for the space. Radio Shack doesn't have low ESR caps, although that might not be a big deal for startup caps. Being non-polarized is the least of its problems.

[ixtlan]

Re: Hannspree HF237

It is 85 so I will just fore-go using it.
And order one in instead.

[ixtlan]

Re: Hannspree HF237

Finally got back to this.
Supplier sent me a new cap to replace the one I blindly missed.
I put it today and results are still not good.
Some details roundup here:
Initial start-up went well and got a screen and it stayed on for over 30 minutes.
So that looking good I rebooted the computer.
Screen came back on and all looked well.
So next step was power cycle the monitor.
Did not come back on but power LED was still on.
Waited for 10 minutes and screen flashed on for 2 sec and then back off.
Turned monitor off and waited 10 min and then back on.
Result was got a screen for about 5 minutes then blank.
Power cycle monitor and on 2sec and off.

I am going for the transformer next.
Will ohm it out and post the results prior to change-out to hear your opinions.
One step at a time and eliminate as I go I suppose.

Too bullheaded to just give up.

[PlainBill]

Re: Hannspree HF237

Symptoms match what I observed with an aging CCFL. But do check the transformers first - it's a lot easier than checking the CCFLs.

PlainBill

[ixtlan]

Re: Hannspree HF237

Hopefully I can get back to this and ring out the transformer today.
But I got a Dishwasher to fix today.
When it rains it pours...

[PlainBill]

Re: Hannspree HF237

Hopefully I can get back to this and ring out the transformer today.
But I got a Dishwasher to fix today.
When it rains it pours...

Or in the case of a dishwasher, leaks over the kitchen floors.

PlainBill

[ixtlan]

Re: Hannspree HF237

Transformer readings:
Meter set to 20k ohms

Transformer has 4 pins on one bank and 5 on the other.
I assume the 4 pin is the primary (1-4) and the 5 pin is sec (5-10)

Primary
1-2 = 0.00
1-3 = Open
1-4 = Open
2-3 = Open
2-4 = Open
3-4 = 0.00
Any Primary to any secondary = Open

Secondary
5-6 = Open
5-7 thru 10 = 0.00
6 - 7 thru 10 = 0.00
7 -8 thru 10 = 0.00
8 -9 thru 10 = 0.00
9 -10 = 0.00


So I am guessing using my rudimentary electrons skills the transformer is good.

Is this a likely conclusion?

[alexanna]

Re: Hannspree HF237

Transformer readings:
Meter set to 20k ohms

Transformer has 4 pins on one bank and 5 on the other.
I assume the 4 pin is the primary (1-4) and the 5 pin is sec (5-10)

Primary
1-2 = 0.00
1-3 = Open
1-4 = Open
2-3 = Open
2-4 = Open
3-4 = 0.00
Any Primary to any secondary = Open

Secondary
5-6 = Open
5-7 thru 10 = 0.00
6 - 7 thru 10 = 0.00
7 -8 thru 10 = 0.00
8 -9 thru 10 = 0.00
9 -10 = 0.00


So I am guessing using my rudimentary electrons skills the transformer is good.

Is this a likely conclusion?

The primary will read real close to 0 ohms resistance, secondary side usually will read somewhere between 500 and 1500 ohms, give or take a few.
You may have to remove the transformer from the circuit to make sure your measuring the correct pins.
The primary windings will be the thick ones, and the secondary will be the thin wires. It is recommended that the secondary windings measure within 3% of each other.