Backlight problem on viewSonic VP171b

[PCBONEZ]

Re: Backlight problem on viewSonic VP171b

You may also have bad tubes.
Try the inverter with different tubes, or the tubes with a different inverter.

A little buzzing is normal.
The windings in the Torrids and transformers can vibrate a little.
It's louder because you have it out of the case.

.

[Starlite528]

Re: Backlight problem on viewSonic VP171b

I replaced the two caps shown with Panasonic/ECG "FC" caps (Digikey # P11217-ND). Problem still remains. The screen works for a while, then dies until it cools off for ten minutes or so. I do hear a faint high pitch buzzing before it shuts the monitor off.

I don't know what else to do, other than replace the whole inverter, which I can't seem to find.

Edit: I found the proper model number on the bottom of the inverter;
PLCD2417414

[Starlite528]

Re: Backlight problem on viewSonic VP171b

I also have the VP171b, but my inverter is the "44.58402.002" model.

The caps are Hermei brand, 180 microfarad, 25 volt. I can not find a matching cap at the local stores, including Fry's.
I haven't looked online yet, but am about to. If I can just replace the caps, that's great.

If I can't find the same spec caps, can I substitute something else?

[mathbee]

Re: Backlight problem on viewSonic VP171b

ok. Thanks a lot for your reply. I will check the transistors and the adhesive on the torroids. Then if the inverter always fails, I will replace both the Hermei caps.

Thanks again!

sebastien

[Krankshaft]

Re: Backlight problem on viewSonic VP171b

Yes your inverter is shot.

You are lucky enough to have a separate inverter module (the little board with the purple probably Hermei crap caps on it).

I would check the SMT driver transistors near the blue caps for shorts with a DMM. If they check out good.

Replace the 2 Hermeiphrodite caps with good Low ESR caps and try to monitor again also check for any cracked solder joints.

KC stated in another post that the yellow adhesive used on the torroid inductors on that board breaks down and eats at the traces so check that too. Remove the inductors remove all of that yellow crap and repair any broken traces.

Check out this thread:

https://www.badcaps.net/forum/showthread.php?t=5043

In a worse case scenario you could always just buy a new inverter module just replace any bad caps on it off the bat so the your new inverter has a long life.

[mathbee]

Hello all,

I've got a LCD from ViewSonic. The model is VP171b. It shows the right image for 1 second when I turn it on and then goes black. Powering it off and on again makes the same.

If I direct a flash light on it, I can see what I should see. It's very dark though. From what I've read, it seems to be an inverter problem, am I wrong ?

and reading the posts, it seems that this is usually related to a dead caps.
The caps of my LCD are (according to another post in badcaps)
PSU:
Li-Shin AREX 94V-0
2 Panasonic 16V 1000uF 105oC HFA
1 Panasonic (unknown value because epoxy covered that side, but it is about 1inhc in round, and what I can see says Ce GH)
1 Rubycon XYG 50V 22uF

Backlight Inverter:
Emax 44.61101.001
2 HERMEI 25V 100uF
1 SSA 50V 2.2uF (M)P1 CE 105oC
4 3kV 22J Ceramic caps
2 250V PMS124J Ceramic Caps

Video Board:
Coretronic Corp
Genesis gm5120 chip
13 Taicon 16V 180uF 0304(M) 105oC (VT)
2 Taicon 10V 1000uF 0304(M) 105oC (HF)
2 Taicon 25V 10uF 0302(M) 105oC (PW)
1 Taicon 16V 2200uF 0238(M) 105oC (PW)
1 Taicon 16V 470uF 0246(M) 105oC (VZ)

I'de like to know what would be the most pragmatic solution for trying to identify bad caps and replacing them as I've never tried to repair a LCD. I put some picture of the LCD boards in attachments.

Can you help me ? Thanks a lot in advance, I'd really like to make this screen works again

sebastien