Samsung Syncmaster 931BF - full white screen

[vrga]

So yeah... Today, more or less out of the blue, my dear monitor decided to white out completely.


Backlight still works, the pixels still work (i think at least), except for the fact that they're all white with the occasional green stripe around the center.


When it went to whiteout, i was doing some web-browsing, and suddenly, you know how a picture shrinks to the center in a flash and disappears on a CRT?

Something similar happened with my LCD, except it went all-white and converged seemingly a bit above the top of the screen (horizontally centered), and stays that way now.

(the above is the best as i can describe the whole effect, note this lasted for barely a second)

Now, i've disassembled it, all the caps are fine, nothing is visually blown, and the only, perhaps "funny" looking thing is on the inverter part of the psu, a part is a wee bit smudged, but i'm unsure if its from factory paste or not.
(will take a picture of it once i find batteries for my digicam...)

The monitor did exhibit a few problems for a while now, most notably, when there were particular shades of brown on screen, a few blocks of the screen would have horizontal strips appearing in and out at around what... 10 or so Hz? (not measured, just me eyeballing from memory, in any case, it was visible, fast and never went away on a few particular shades)



Anyhow, if anyone can hep me, i'd be very grateful.

Now for board designations...

The video board (DVI, VGA connectors and the LVDS cable)
Model: Mendel_RTA
Code no: BN41-00710A
Rev: MP 1.0 06.03.13

The big chip in the middle of that board (scaler chip iirc?) has the following on its sticker...

MD17-D0CAa-1009
27.04.2006.
(54FB)


On the underside of that board is a sticker with the following:
400049489 / Ver: 00007
BN91 - 01056A U SAC1 MD17-1009



The PSU board says its a PWI1704SV (A) board, Rev 1.3
It has various CapXon capacitors and such, thats about as much as i can glean from it.

Had my father look over it, and he suggests that we go over all the voltages when the thing is turned on, so we'll do that tomorrow morning. Fresh eyes might spot some other things weary eyes didnt.

(no worries, he's a retired electrotechnics engineer, so at the very least, we at least know how to make sure not to electrocute ourselves)




So very sorry for the big wall of text, i tried to use as many paragraphs as reasonably possible to keep the readability around



I appreciate any potential feedback


Cheers


[edit] upon further review, the LVDS connector to the panel itself was solidly in, but i'll try reassembling the whole thing, just in case.

[jetadm123]

Re: Samsung Syncmaster 931BF - full white screen

Hint: A lot of members won't even consider helping you without photos. To be fair, we have to see what you're seeing in order to provide help. Without photos is like asking you to take voltage readings with your eyes closed.

A white screen can be caused by a fuse going out on the LCD control board. This board is at the top of the monitor and usually spans the width of the monitor and is connected to the LCD panel by a series of flat ribbon cables.

[PlainBill]

Re: Samsung Syncmaster 931BF - full white screen

A possible cause (about the only repairable one) is a failure of the fuse on the panel board. It's usually hidden behind the metal panel at the top of the LCD panel. Pictures will help us point it out to you.

PlainBill

[vrga]

Re: Samsung Syncmaster 931BF - full white screen

pics coming right up.

first pic is the lcd when powered up and assembled, the following 8 are from the panel's logic board, the 6 after that are the from the PSU and of the "funny" spot i mentioned and the last six are of the logic board where the DVI, vga and LVDS connectors are located.

I hope the pictures are crispy clean enough As a side note, i can finally read the damn tiny parts as well

[jetadm123]

Re: Samsung Syncmaster 931BF - full white screen

Refer to photos. Try checking fuse F5. If it checks ok, then try measuring the output of voltage regulator U1.

[vrga]

Re: Samsung Syncmaster 931BF - full white screen

will do tomorrow, its 4am now, and i dont want to risk poking it in the wrong way with a multimeter.



thanks

[shovenose]

Re: Samsung Syncmaster 931BF - full white screen

why dont you get some sleep then


my suggestion: replace the capxons (except the big one) and see if that fixes it. caps can fail w/o bloating

[vrga]

Re: Samsung Syncmaster 931BF - full white screen

the F5 fuse reads 0.3 ohms if i'm reading my multimeter right, so i guess its okay, and as for the VRM, we'll take a look in a few minutes/hours/something, since we plan to figure if the PSU is also giving out the correct voltages, and both me and my father have a feelin that the 5V line might be going a bit wonky. We'll see soon.. I'll get back here with the readouts when we do figure out the stuff


shovenose, well, it being a saturday now, there's no way that i can replace the caps today. and i'd rather hold off that investment when we've tracked down the other possibilities.



Also as third thing, can anyone help with identifying the manufacturer and finding a datasheet for that particular VRM that jetadm123 identified?

[PlainBill]

Re: Samsung Syncmaster 931BF - full white screen

the F5 fuse reads 0.3 ohms if i'm reading my multimeter right, so i guess its okay, and as for the VRM, we'll take a look in a few minutes/hours/something, since we plan to figure if the PSU is also giving out the correct voltages, and both me and my father have a feelin that the 5V line might be going a bit wonky. We'll see soon.. I'll get back here with the readouts when we do figure out the stuff


shovenose, well, it being a saturday now, there's no way that i can replace the caps today. and i'd rather hold off that investment when we've tracked down the other possibilities.



Also as third thing, can anyone help with identifying the manufacturer and finding a datasheet for that particular VRM that jetadm123 identified?

It appears you have a good handle on this. Do verify power is getting to the panel board.

The 1117A family of parts are LDO (low drop out) regulators. They are available in both fixed and adjustable versions, this appears to be an adjustable version. Fixed versions are identifiable by the part number - MM1117-3.3 would be a 3.3V fixed regulator while MM1117A is the adjustable version. Google 1117A for datasheets. I'm not aware of who uses the MM prefix. There IS a part from Mitsumi called an MM1117, but that's an entirely different part.

These parts are of a group often referred to as 'jelly bean' parts - available from a wide variety of manufacturers, but interchangeable at the manufacturing level.

I fully concur with your idea - first get the LCD display working, then address the capacitor issue.

PlainBill

[vrga]

Re: Samsung Syncmaster 931BF - full white screen

so we measured it,on the three pins of the VRM (U1 on the panel logic board itself), compared to the common ground line, from left to right the voltages are as follows:

ADJ(pin1):2.2V
Vout(pin2): 3.46V
VIN(pin3): 5.10V

We unfortunately only measured these voltages since getting to anything else in the psu and logic board was a bit too risky for our tastes, and these things need to be measured with the "normal" running condition anyhow.

We also rechecked the picofuse F5 under load, its good.


waiting eagerly for your replies fellas


Also,while powering it up, the whole PSU squealed a bit differently than from its usual mode of operation. Started off with a higher-pitched squal (power on, screen didnt start yet), bit of chirping around while going down in pitch (my guess would be that the inverter starts drawing power at this point) and then a sudden drop to a constant low-pitch buzz (monitor lights up at this point, backlight and full white screen).

unfortunately my ears arent good enough to guess the correct pitch of the various pointsin Hz, but then again, i dont work with this stuff regularly....

also, i'm almost 100% sure that the wave i heard was a sawtooth wave, since its very distinct from the sine, square or triangle waves.



Hope this extra info helps



also, i'm attaching the datasheet that i believe is the right one for the before mentioned VRM.

[jetadm123]

Re: Samsung Syncmaster 931BF - full white screen

Since schematics for LCD panels are next to impossible to find, it's hard to say if the 3.46V output for U1 is correct. Looks like the 5V is ok. You may want to check the LCD logic board for additional fuses. Also, check the video logic board to see if there are any fuses. Unfortunately, due to the lack of info for these panels, the success rate for repair is relatively low.

[rukfas]

Re: Samsung Syncmaster 931BF - full white screen

Hi,

I have a gericom model with similar panel board and the same problem and just fixed it. The problem was Q3 transistor. I'll post some pics tomorrow.

[vrga]

Re: Samsung Syncmaster 931BF - full white screen

oh?


on which part of the whole thing is it? Panel, PSU or the logic board?

[rukfas]

Re: Samsung Syncmaster 931BF - full white screen

It's panel board, and in a few hours i will post pictures, as soon as i get home.

[vrga]

Re: Samsung Syncmaster 931BF - full white screen

mmkay.


from looking on the pics of the panel board i posted, there appears to be only the Q16 and q6 transistors.

[vrga]

Re: Samsung Syncmaster 931BF - full white screen

rukfas, any pictures?

[Warlocke]

Re: Samsung Syncmaster 931BF - full white screen

Apparently this model is just getting to be a certain age, because my Samsung Syncmaster 931BF just keeled over a few days ago. Black-screen. So I guess it's a bad season to be a 931BF.

I cracked it open last night and, sure enough, three bulging CrapXon capacitors (two 820uF 25V, and one 470uF 25V).

I'm debating on whether I should replace all the capacitors while I'm at it, rather than just the three bad ones. I know there are prepacked bundles of the correct caps to be had online, rather than hunting them down individually...

Either way, I've never soldered a darn thing before, so look out world.

vrga: Good luck with your monitor; buying new ones is an expensive prospect (and one to which I hope neither of us ends up resorting).

[vrga]

Re: Samsung Syncmaster 931BF - full white screen

Warlocke, i got a "new" one from my sisters husband, a NEC 1970NX. S-IPS panels ftw


but the samsung is still highly on my "to-fix" list since i have 3 other people i live with who'd like to get rid of the crt's :p



As a side note, mine didnt have any bulged or busted caps. CapXon's too.

[retiredcaps]

Re: Samsung Syncmaster 931BF - full white screen

I'm debating on whether I should replace all the capacitors while I'm at it, rather than just the three bad ones. I know there are prepacked bundles of the correct caps to be had online, rather than hunting them down individually...

Capacitors die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

Most members here will recommend that you replace ALL capacitors with reputable brands from reputable sellers. Brands like Rubycon, Panasonic, and United Chemicon are suggested. A list of recommended caps can be found at

https://www.badcaps.net/forum/showthread.php?t=2280

Either way, I've never soldered a darn thing before, so look out world.

If you have an old board lying around, practice on that.

[retiredcaps]

Re: Samsung Syncmaster 931BF - full white screen

Either way, I've never soldered a darn thing before, so look out world.

Forgot to mention a great soldering video by CuriousInventor at

http://www.youtube.com/watch?v=I_NU2ruzyc4

Also, this site has a good solder writeup with excellent pics at

https://www.badcaps.net/forum/showthread.php?t=485