Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

[chevelle_nut]

First of all I would like to thank everyone involved in this forum, I have lurked here for a long time and found MANY great posts that I have used to save the lives of all kinds of electronics.

Now it's my electronics that are broken. I have a Samsung Syncmaster 710mp LCD TV/monitor that I use as my everyday computer monitor, DirectTV monitor and cable TV. For awhile now the cf have been flickering on the VGA input. The Svideo/composite inputs and the tuner all display fine. I popped it open and found one bulged cap(470μf 25v) on the power supply/inverter board near the regulators. I replaced it with a rubycon and it worked great... The problem seemed resolved but 2 days later it's doing the same thing again. Am I chasing a symptom but not a cause ? I read somewhere that a shorting regulator might be the culprit but as the other functions are goo I am at a loss as to where to start changing regulators.

Thanks in adavnce

[weirdlookinguy]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

You need to replace ALL the caps in the monitor, and then go from there.

[chevelle_nut]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

I don't feel that just replacing all the caps is really a viable troubleshooting technique, I can just buy a new board for $53. It seems as though the VGA function works fine for awhile then the inverter drops out. The strange thing is as soon as I change to TV or video source the ccfl's pop right back on. When I go back to PC the screen is still on, but fades out to black. If I stay on TV or Video the ccfl's stay on nice and bright. I believe the problem not to be the inverters but rather some function of the VGA. The computer outputs fine to other monitors and the Samsung does the same fade out with other computers. The problem seems heat related somehow but odly enough it was totally gone when I swapped out that cap. I wonder if it changes the primary supply on the inverters when running the PC Input?

This Ebay listing has some nice pics of the board.
http://cgi.ebay.com/Samsung-Power-Su...3286.m20.l1116

FYI I thought I put in Rubycon, turns out it is a Panosonic FM

[PCBONEZ]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

If by 'viable" you mean proper,,, well, as you already know you have a bad batch of caps 'proper' would be to remove each cap and test it with an ESR -and- a capacitance meter.
Then you put the ones that are still good back in and replace the rest.
Of course, if you don't have those meters and since with them you'd have to take most of the caps out anyway you could just put in new reliable caps and save some time.

You already found bloated caps.
Any like that one (same make) are probably also bad. - 99.9% chance.
Except for Easter-Egging (pulling things out and checking them at random) you can't trouble shoot much else until that's fixed. Any checks with power applied will be meaningless because bad caps will affect voltages.

Yup, you can spend $53 and get a new one.
Odds are it will have the same kind of short-life caps you already have...
... but you could do it.

[Note: Board in your eBay photo shows it has CapXon caps. Known high failure part in LCD screens -and- probably the same ones that went bad on your board.]

And,,, those kind of circuit boards are OH SO EASY to work on.
- - But it's up to you.

[FM are fine for that.]

.

[Wizard]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

Oh,

That 710mp have a linear regulator appox in middle of mainboard left of the big square chipset (gullwing SMD). There is 2 caps on both sides of this regulator. It is SMD aluminum electrolytic caps. I upgrade them to 220uF even 470uF low ESR, I use regular capacitors, leads snipped close and legs bent out 90 degrees and solder them to the pads. Here is, when regulator heats up, and the marginal caps. The Q of the circuit changes and makes the regulator more suspecible to oscillation corrupting the display.

That was TOUGH case to solve as the AC oscillating riding on DC was only visible when voltage division was set around 20mV (small) on the scope.

Take a picture of your mainboard not the power supply and I'll point out the caps in particular?

Cheers, Wizard

[chevelle_nut]

Picture of video board from 710MP

Here is the picture you requested

[Wizard]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

Change caps in circled:

http://www3.sympatico.ca/jpero/allpa...0MPcircled.jpg

Do have enough height to use regular low ESR electrolytics with bent leads to the solder pads for the SMD electrolytic capacitors. I hate those as they are always bad on heat and ESR goes way up, simply grasp the cap with needle nose pliers and push down while twisting back and forth till leads breaks, flick off the remaining leads with your soldering iron.

Cheers, Wizard

[chevelle_nut]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

O.K. so now it gets weird. I'm looking over the caps you circled to make my grocery list. I notice that in many places there is what I'll call flux residue on many of the surface mount components, on the device leads and covering entirely some of the smaller (resistors, caps ,connectors) components. I grab some swabs and isopropyl and start cleaning as much as I can find. Just for giggles I leave the back off and connect up the power cord and vga. Turn it on and it almost immediately starts the dark/light flickering. I was trying to use my can of dust remover to cool down the chip that Wizard mentioned in his post. To see if it was climbing in temp, and if cooling it would show improvement. As soon as I hit it the screen went right back to full illumination. The brightness is great and no sigh of a flicker. I left it running for over an hour or so now and it still looks perfect. I have no idea if it was the thermal shock or if I may have dislodged some residual gunk from the circuit but it looks like a small miracle has occurred. I'm going to power it down and reassemble the case. After that I'll probably going to catch up on some Tivo. In the morning I'll go back to the PC and post what happens.

Fingers crossed.

[PCBONEZ]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

FANTASTIC!

Now:
Check that the 'stuff' you cleaned up didn't ooze out of the caps.
Check for bad solder joints. (Pretty common problem.)

[chevelle_nut]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

Looks like it's still messed up, this morning I turned it on and it flickered a bit, then a minute later (about the same time as I grabbed the dusting spray last time) it snapped into full bright mode. I'm sad to report it must have been coincidence. This time I used it for at least 2 hours before heading off, I left it running. When I returned it is back to the "dark" mode. Same as before, when I switch sources it lights up just great. In fact I watched it on the S video connection for the rest of the day without incident. And whenever I toggle thru the inputs back to PC it displays for a few seconds then back light drops out. I guess I'm stuck trying to rehab it.

The ooze I cleaned off didn't necessarily coincide with cap placement on board so I'm still under the belief that it was flux from a reflow/rework scenario. Some of the joints even look to be hand reworked (ewww). I see what you mean by poor solder joints. On the picture of the video board that Wizard circled there are only 2 "regular" lytics the rest are the aluminum variety,when those fail are there any visible signs ?

Now I need to source the caps to replace the circled ones. Wizard, you mentioned upgrading some sizes to low esr radials. Here is the list of values currently on the board starting at the top and working around clockwise.


47uf 6.3v (2)
22uf 35v
10uf 16v
100uf 25v
100uf 16v (2)
47uf 16v

Which of these should I upsize?

Then I need to find a source, TC doesn't list the small stuff...

I guess while I'm at it I'll recap the PS invertor side too.

I need:
1000uf 10v (2)
470uf 25v
1uf 63v
1uf 50v
220uf 25v
4.7uf 50v

there are 2 others I can't get to the values for, The big one glued down on the side with the value. There is another one right next to lower heatsink I would have to pull to read.

Anyone wanting to quote me on this stuff can PM me.

[PCBONEZ]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

Where are you (Country)
In USA/Canada Digikey and Mouser are popular. (Just add ".com")

Assuming Digikey and that the caps physically fit (physical size):

I would use Panasonic FM for:
47uf 6.3v (2)
100uf 25v
100uf 16v (2)
47uf 16v
~~~~
1000uf 10v (2)
470uf 25v - - Maybe use 35v for this one if fits.
220uf 25v - - Maybe use 35v or 50v here, if one fits.

And either FM or FC or Nichicon PW for:
22uf 35v
10uf 16v
~~~~
Use KG if available below 10uF.
1uf 63v
1uf 50v
4.7uf 50v

FM and FC are sometimes physically bigger than comparable uF caps from other brands so make sure you check size details and space requirements before ordering.
Knowing Digikey's stock Chemicon KZE would be the next I'd check if you can't match one up to FM. (Next after FC or PW too for that matter.)
- Then HE or KY, then LXZ.
I prefer KG for less than 10 uF and 50+ volts. They are smaller and better rated caps at that end than the others but from about 4.7uF (as I recall) FC and PW are rated better.
- VZ series only if there are no other options of those I already mentioned.
In some sizes VZ is the only choice in 105 C rated caps.

~~~

The big huge cap is on AC input and they rarely fail unless you've had a power surge.
[Same-Same in PC Power Supplies.]
If it's not actually bloated I wouldn't worry too much about that one.

Sometimes if you can't read one a really shinny knife blade [with assistance of a small flashlight] can be used as a mirror to get the number off it without actual removal. In conjunction with that sometimes the ability to hold a knife, a flashlight, AND a magnifying glass (with your toes?) helps too.

.


.

[chevelle_nut]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

Thanks for the guidance, the box just arrived from Digi-Key. I'll get some pictures posted as I go through it.

I'm going to recap the PS board while I'm in there.

"cover me, I'm goin' in"

[weirdlookinguy]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

Best of luck to you. Be sure to let us know how it goes.

[chevelle_nut]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

Well, I finished the video side. Turned it on and got flicker right away. Then it straightened out for a while, seemed o.k. then... dark. toggled thru inputs and it stays on vga for a longer time. we'll have to see.

Here is a pic of new caps on video side:

[chevelle_nut]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

whoa I could have sworn I shrunk that pic !!!

[PCBONEZ]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

The caps I circled in your photo are SMD electrolytic.
The vent stamp marking in the top is the give-away.
Can't tell manufacturer.
They are 470uF 16v and that's big enough to be of concern.

[Wizard]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

This is audio ampifier/audio processing. Not so crtical.

Cheers, Wizard

[chevelle_nut]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

Day 2, it's still out of the case, but it's working. Nice and bright on vga, and still just as good as it's ever been as a Tivo monitor ! I haven't replaced any more components than the ones in my photo. The flickering on startup I haven't noticed. I'm almost afraid to repackage it.

I looked at the X marked ones but the tops are still nice and flat, I think the lighting in that pic makes them look bulged.

[PCBONEZ]

Re: Samsung SyncMaster 710mp TV/Video fine, but on VGA goes dark

I wasn't saying they looked bad.
Just saying check 'em.
.

[chevelle_nut]

The latest update...

I went back in and replaced the 'lytic caps on the power supply side. All but 5, 4 are in the inverter, 1 was the one I couldn't read the value of. Turns out to be a 47uf @50v. The 4 little ones are 47uf@25v. As soon as I need some other parts I'll put them on an order too.

The monitor started up o.k. not full bright and a little flicker, but so far it's viewable. we'll keep an eye on it.