Samsung Syncmaster 931BF - full white screen

[jetadm123]

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...

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).

Note: If you do decide to purchase a "kit" from Ebay, make sure they include ALL the caps. Sometimes, the seller does not include the smaller caps. And these caps are some of the most important ones.

[Warlocke]

Re: Samsung Syncmaster 931BF - full white screen

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

Hehe. That's good to hear. I'm currently using a 13 inch fishbowl from the late Mesozoic era that my sister discarded about a decade ago. I keep thinking I should look around the monitor to see if the picture wraps to the other side.

On the upside, when I do get my LCD working again, it will certainly feel like I've got a huge new monitor.

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

Thanks for all the advice. I certainly plan on practicing, and I have enough old junk around the house for it.

I was planning on getting in some practice anyway, since I'm going to be connecting Cat5 to a circuit board for a joystick I've been working on. All the other wiring was done by crimping on quick disconnects, and I've been putting off the soldering.

Note: If you do decide to purchase a "kit" from Ebay, make sure they include ALL the caps. Sometimes, the seller does not include the smaller caps. And these caps are some of the most important ones.

Interestingly enough, the first one I spotted had all but the largest cap (KM105°, 100uF 450V).

[retiredcaps]

Re: Samsung Syncmaster 931BF - full white screen

Interestingly enough, the first one I spotted had all but the largest cap (KM105°, 100uF 450V).

The general attitude towards the biggest cap is that it rarely, but not never, fails.

Incidentally, it is also the most expensive cap ranging around $2 to $4 depending quality, brand name, etc.

Definitely have a look at the CuriousInventor solder video. I have watched a lot of soldering videos when I first started and that by far is the best.

[EGuevarae]

Re: Samsung Syncmaster 931BF - full white screen

The general attitude towards the biggest cap is that it rarely, but not never, fails.

I agree.Just replaced one in more than a hundred units ....

[kingofcoins]

Samsung Syncmaster 931B....>Similiar P/S in Princeton VL1918

I'm doing a Princeton VL1918 with no display and typical bad swollen caps made by 'Craps-On', and I noticed how similiar the layout, RF shield and boards are to Samsung 931B's I've done in the past. While here I have some pics and a couple questions for you vets.
My first pic show the P/S inverter board with the bad caps and circled in red is a tough plastic sleeve, marked FIT V2, that was on the 330uf cap next to the transformer. So what is the purpose of such sleeves and should I replace it on/with the new cap ? I note other components near heat sources may have them as well. They do tend to hide and disguise a cap so look closely.
My second pic and question is about the A/V boards found in these units. Mine has 18 caps, mostly of green with gold stripe Teapo Series SC, and some smaller caps in SH. None were replaced and LCD works fine now. The question is since I don't read a lot about folks repairing this side of the board so to speak, what do you vets say about doing so ? Some insight on what goes on in A/V circuit boards and what to do about them during repairs would be a great value to us newcomers and weekend techs as well.
Thanks!

[PlainBill]

Re: Samsung Syncmaster 931BF - full white screen

I'm not sure why the plastic sleeve is used. The two possibilities that come to mind are mechanical protection, and protection from heat. Neither make a lot of sense.

As far as teh caps on the 'A/V' board (I call it the logic board), unless there is an obvious fault, I don't touch them. They are not under the same stress as those on the power supply.

PlainBill

[EGuevarae]

Re: Samsung Syncmaster 931BF - full white screen

I'm not sure why the plastic sleeve is used. The two possibilities that come to mind are mechanical protection, and protection from heat. Neither make a lot of sense.

As far as teh caps on the 'A/V' board (I call it the logic board), unless there is an obvious fault, I don't touch them. They are not under the same stress as those on the power supply.

PlainBill

I second that. No need to change them unless you are positive they are damaged/failing.

[momaka]

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

Output voltage is a bit high for U1, but I doubt this is the problem. Let's assume it's fine for now.

I'm guessing the panel in this monitor is a HannStar. Just fixed two of these with a white screen this week - one was a SyncMaster 931B (fix to be posted in a few days). In both cases, it was shorted ceramic caps (in different parts of the circuit, though). The two I fixed had a slightly different layout than yours, but overall they have the same basic design.

With that said, I think the first thing you want to get is the AAT1164 datasheet (component U11) - this is the IC that controls/produces voltages for the LCD buffers. The datasheet will give you a pretty good idea of the circuit.

Next, power on the monitor and see if U11 gets hot at all. If not, see if D10, Q6, Q16, D20, D21, or D60 get hot.

If not, check the voltage with your multimeter between ground and the little pad labeled "AVDD1" (this is "Vout1" in the datasheet). Could be anywhere between 5v and 28v, probably closer to 10v-13v.

Let me know what results/readings you get.

[jetadm123]

Re: Samsung Syncmaster 931BF - full white screen

Output voltage is a bit high for U1, but I doubt this is the problem. Let's assume it's fine for now.

I'm guessing the panel in this monitor is a HannStar. Just fixed two of these with a white screen this week - one was a SyncMaster 931B (fix to be posted in a few days). In both cases, it was shorted ceramic caps (in different parts of the circuit, though). The two I fixed had a slightly different layout than yours, but overall they have the same basic design.

With that said, I think the first thing you want to get is the AAT1164 datasheet (component U11) - this is the IC that controls/produces voltages for the LCD buffers. The datasheet will give you a pretty good idea of the circuit.

Next, power on the monitor and see if U11 gets hot at all. If not, see if D10, Q6, Q16, D20, D21, or D60 get hot.

If not, check the voltage with your multimeter between ground and the little pad labeled "AVDD1" (this is "Vout1" in the datasheet). Could be anywhere between 5v and 28v, probably closer to 10v-13v.

Let me know what results/readings you get.

Hello Momaka! Great to hear a success story on someone actually fixing a white screen problem. One would have expected to see a Samsung LCD panel within a Samsung monitor. Anyways, on the the panels you repaired, what model Hannstar panel was used?

[momaka]

Re: Samsung Syncmaster 931BF - full white screen

Sorry for the delayed response.
The panel in the Samsung 931B is HannStar HSD190ME13-D10 Rev:2. Problem was a shorted ceramic cap on the boosted 12v rail on panel board (this would correspond to "AVDD1" on vrga's monitor).
The other panel is from a HP w19b monitor, and it's a HannStar HSD190MGW1-B00 Rev:1.
Hope this helps.

[Warlocke]

Re: Samsung Syncmaster 931BF - full white screen

How would I go about identifying the ripple current value on the caps that I'm replacing?

Bearing in mind that I can't afford to pay more than the price of a new monitor for measuring equipment, should I simply shoot for as high a value as I can while still being able to physically cram the replacement caps in the monitor?

Or are the CapXons so poor that any Panasonic caps I get to replace them would easily have a higher ripple current value than the ones I'm replacing?

Thanks again!

[What with the holidays, I haven't even gotten around to fixing this, and now my stereo receiver suddenly quits working. Is it 2011 yet? ]

[retiredcaps]

Re: Samsung Syncmaster 931BF - full white screen

How would I go about identifying the ripple current value on the caps that I'm replacing?

Identify the current caps and search for its datasheet.

Bearing in mind that I can't afford to pay more than the price of a new monitor for measuring equipment, should I simply shoot for as high a value as I can while still being able to physically cram the replacement caps in the monitor?

An ESR meter costs between $60 to $300 dollars.

Or are the CapXons so poor that any Panasonic caps I get to replace them would easily have a higher ripple current value than the ones I'm replacing?

PCBONEZ talks about ESR/ripple, etc at

https://www.badcaps.net/forum/showpo...30&postcount=7

And yes, Capxons have a very poor reputation on this forum.

[Duke7213]

Re: Samsung Syncmaster 931BF - full white screen

Check the solder joints on the rectifying diodes and capacitors. If a joint goes bad, you may still get the proper voltage on your meter but then you are putting a load on your filtering capacitors - hence one of the reasons the caps go bad! Recently fixed a 931bf and a force feedback joystick - both had bad solder joints. I'm anticipating a future cap job for the 931bf.

Duke7213

[A43]

Re: Samsung Syncmaster 931BF - full white screen

Hi Guys,

I have a Samsung 931BF with all lines and distortion on screen when powered up, without any display cable plugged in - see Pic1.

I disassembled, took out the main pcb, and could no sign of any burst capacitors or heat damage.

The only thing I saw was some marks on the back of the pcb - see Pic 2 - which I cleaned off and reassembled to test, with no change, still the same lines and distortion.

I am just wondering if anyone has seen similar lines, and if so was it the capacitors, or the transformer.

I can do some basic checks with a fluke meter, but that is the only tool I have for testing the pcb.

I would like to try identify the correct parts before ordering same.

Has anybody come across a complete new pcb board, and if so is it expensive.

I like this monitor, and would like to repair it.

Thank You,

A43

[cyjun1990]

Re: Samsung Syncmaster 931BF - full white screen

Let me repair

[momaka]

Re: Samsung Syncmaster 931BF - full white screen

Hi A43,
the problem you're having could be caused by many things: bad caps, bad connection on the LVDS cable between the logic and t-con boards, or bad tab bonds on the LCD panel. Therefore, I suggest you post more pictures, especially of the power supply top side and logic board top side. Also, clean the LVDS connector with some IPA (Isopropyl Alcohol).

[/b/tard]

Re: Samsung Syncmaster 931BF - full white screen

yall trying to fix these in 2010 and here I am 11 years later with one that just died on me
KEK