Sun / Samsung 24" warmup issues

[gerryg80]

First thanks in advance for this forum, I've learned a ton in just a few days. One of the most valuable resources I've ever run across on the web -- I didn't have any particular interest in troubleshooting electronics but after what I'm reading here this could be a pretty cool new hobby.

I have 2 of the same monitor as in this thread, from a group buy about 5 years ago. All the ones I'm aware of are having similar issues to what I describe here to varying degrees, a couple of people gave up, another one had his professionally repaired, etc.

https://www.badcaps.net/forum/showthread.php?t=14767

Started as occasional noise on the screen when the monitor was cold -- in particular noticed last summer it took well over an hour to come back when we had been on vacation for a week and it was unplugged. Progressed until about 2 weeks ago when I got nothing but noise even when it was fully warm.

Coincidentally the same day mine died completely one of my friends successfully revived his by replacing two bad caps. First I had heard of that problem and even he hadn't heard about this forum.

So based on his experience I searched and found this board. Decided to try my own repair -- I'm pretty handy for everything from plumbing to drywall and I have a mechanical engineering degree (from the univ of misery at Rolla) but soldering electronics was new for me. First I replaced the 3 1000uf x 35v caps -- all of those were domed. No luck, monitor still came up to nothing but noise. So then I replaced the other 9 radial caps (other than the large one in the center of the board).

Still the monitor came up to noise but this time I let it get fully warm -- I had already given up so I wasn't timing it but somewhere around an hour and 3 beers later it suddenly locked on to the signal and then was fine for another 3 hours.

Powered it down overnight and back on this morning (6 hours), it came back immediately and without any hint of noise, looked as good as it did brand new. Again, unplugged it before going to work this morning -- 13 hours later I powered it on and this time it came back but still went through several short episodes of "noise" before it was stable. All within maybe 3 minutes and then it's been stable for well over an hour.

so... it seems to be completely usable but clearly there is some remaining issue when cold. Any thoughts? Replace the big cap too? Not worry about it?

tl/dr: outstanding forum -- seemed to have mostly fixed my monitor and wouldn't have even attempted it without this forum as a resource but still have a slight lingering issue when cold.

[retiredcaps]

Re: Sun / Samsung 24" warmup issues

so... it seems to be completely usable but clearly there is some remaining issue when cold.

An SMPS power supply requires low ESR (equivalent series resistance) caps.

Most retailers like Fry's and Radio Shack only sell general purpose caps. While they may work, they don't last long or work properly.

If you did not install the proper low ESR caps or if you skipped a few because they weren't bloated, this could be your problem.

See my standard answer (regulars may skip the URL)

https://www.badcaps.net/forum/showpo...84&postcount=3

So the question is what brand and series did you use for replacements? For example, Panasonic is the brand and FM is the series. FM are low ESR caps.

[gerryg80]

Re: Sun / Samsung 24" warmup issues

An SMPS power supply requires low ESR (equivalent series resistance) caps.

Everything I replaced was stamped with a 105C rating -- I asked for Low ESR at one place and got a confused look so just said "High Temp".

I got most of the caps from Parts Express but unfortunately didn't pay that much attention to the brand -- they stock Lelon. I do have one nichicon from a different place because Parts Express had no equivalent.

I started with only the 3 obviously bad ones but then when that didn't work your standard answer is actually what led me to replacing everything else but the big one in the middle (12 total).

Now I'm wondering if I shouldn't have replaced it too?

[retiredcaps]

Re: Sun / Samsung 24" warmup issues

Everything I replaced was stamped with a 105C rating -- I asked for Low ESR at one place and got a confused look so just said "High Temp".

105C doesn't mean it is low ESR.

I started with only the 3 obviously bad ones but then when that didn't work your standard answer is actually what led me to replacing everything else but the big one in the middle (12 total).

Now I'm wondering if I shouldn't have replaced it too?

You can try replacing the largest cap, but my guess is that the other caps are NOT low ESR. Low ESR caps are Panasonic FR, FM, or FC series. All available at digikey.com.

[gerryg80]

Re: Sun / Samsung 24" warmup issues

105C doesn't mean it is low ESR.



You can try replacing the largest cap, but my guess is that the other caps are NOT low ESR. Low ESR caps are Panasonic FR, FM, or FC series. All available at digikey.com.

okay I was afraid of that after seeing your first post. Parts-Express has a local storefront in addition to the website. That's where I got the low ESR reaction -- their website does claim the parts I bought are suitable for SMPS.

A further search on Mouser reveals the parts I bought are a series that is 105C rated but apparently not low ESR because Lelon has a different series that is low ESR. Sigh.

Strange that the monitor works really well after warm up and in fact even the warm up issues are nearly identical to what it was doing 9 months ago. That's what led me to the "must be something I haven't changed yet" conclusion.

Thank for the info

[retiredcaps]

Re: Sun / Samsung 24" warmup issues

Strange that the monitor works really well after warm up and in fact even the warm up issues are nearly identical to what it was doing 9 months ago.

As the lcd monitor warms up, the general purpose (i.e NOT low ESR) capacitor's ESR drops which it allows it work. A low ESR capacitor doesn't need to warm up.

The difference between the two can be an order of magnitude. For example, a general purpose 1000uF 16V cap might have an ESR of 0.2 ohm. The same low ESR 1000uF 16V cap might have an ESR of 0.020 ohms or 10x less.

[gerryg80]

Re: Sun / Samsung 24" warmup issues

As the lcd monitor warms up, the general purpose (i.e NOT low ESR) capacitor's ESR drops which it allows it work. A low ESR capacitor doesn't need to warm up.

Thanks, that would definitely explain the behavior I'm getting. That also makes it sound like the original caps initially failed in a way that they stopped working like low ESR and had higher resistance till they were warm?

Anyway I'm working up a purchase of actual Low ESR caps to fix 5 of these now. Glad I checked here before I tore into a second monitor.

[retiredcaps]

Re: Sun / Samsung 24" warmup issues

See

http://en.wikipedia.org/wiki/Equival...ies_resistance

Capacitors

A very serious problem, particularly with aluminium electrolytics, is that ESR increases over time with use; ESR can increase enough to cause circuit malfunction and even component damage,[1] although measured capacitance may remain within tolerance.

[retiredcaps]

Re: Sun / Samsung 24" warmup issues

As the lcd monitor warms up, the general purpose (i.e NOT low ESR) capacitor's ESR drops which it allows it work. A low ESR capacitor doesn't need to warm up.

BTW, I'm not a technical expert in the above area. I'm just trying to explain in a way most people can understand it as we have a wide audience and possibly people using google translate.

PS. Shipping costs from digikey using USPS 1st class is a very reasonable $2.75ish USD and you get the caps in about 2 to 3 days.

[gerryg80]

Re: Sun / Samsung 24" warmup issues

Most of the caps on the board are a CapXon series KM. I pulled the data sheet and unless I misunderstand these are just standard 105C rated caps and not low ESR?



There are four CapXon series GL caps, including the first 3 I replaced (1000uf 35v) and a 4th I didn't replace till the second go-round (2200uf 10v).



So here's my what I would replace these with from panasonic, based on the digikey website. Only confusion on my part is that CapXon quotes "impedance" in their spec sheet where I'm comparing that to ESR at DigiKey.

CapXon GL 1000uf 35v, ripple=1930ma, Impedance = 36mOhm
Panasonic FR 1000uf 35v, ripple=1985ma, ESR = 29mOhm?

CapXon GL 2200uf 10v, ripple=1690ma, Impedance = 40mOhm
Panasonic FR 2200uf 10v, ripple=2470ma, ESR = 18mOhm

[budm]

Re: Sun / Samsung 24" warmup issues

They are the same, impedance is not pure resistance (it is complex resistance that has to do with inductance/capacitive reactance/pure resistance), same for ESR is also.

Bottom line, the FR has lower ESR than the CapXon.

[retiredcaps]

Re: Sun / Samsung 24" warmup issues

Most of the caps on the board are a CapXon series KM. I pulled the data sheet and unless I misunderstand these are just standard 105C rated caps and not low ESR?

Correct. When you don't see the words "low ESR" or impedance listed on a datasheet, they are general purpose caps.

Now you can use what we call "entry level" low ESR caps like Panasonic's FC for general purpose cap replacements. I haven't checked the datasheet, but I'm assuming the ripple characteristics of FC is the same or better than Capxon KM.

Panasonic FM/FR have even "better" ESR characteristics than FC.

I hope I explained that clearly enough?

PS. Don't forget to check cap's height and diameter so the enclosure fits after they are installed.

[gerryg80]

Re: Sun / Samsung 24" warmup issues

Took a bit to get the right caps ordered -- panasonic FRs worked for the 1000uf 35v, but the FR version of the 2200uf 10v was in danger of hitting the heat shield at 25mm. So I had to go with the FM version there which is only 20mm tall. (to be clear, I didn't order parts that wouldn't fit, just had a hard time finding both the right parts from the same place). The remaining caps I initially replaced met or exceeded the original CapXon specs so I left them alone.

Got it all back together hooked it up to my laptop, and got virtually an identical display to what I saw after the previous two repair attempts -- top 3rd of the screen had a sort of recognizable image while still noisy, but below that it was just random noise. I didn't leave it on for even a minute and unplugged it.

Had to leave it for an hour or so but then came back to set it up to take pictures for this post, and this time it worked perfectly as soon as it was attached to the laptop. No hint of any noise and has been working for over an hour that way.

Not quite sure what to think. Guess I'll see how it behaves over the next few days.

[budm]

Re: Sun / Samsung 24" warmup issues

All the cables are properly seated?

[jetadm123]

Re: Sun / Samsung 24" warmup issues

Sounds like either a bad solder joint, or possibly bad caps on the main/logic board. Try heating up the power supply and/or the logic board with your blow dryer (yes, the same one you use for your hair) to see if you can shorten the time till you get a good display. Hopefully, you'll be able to isolate which board is causing the problem.

[gerryg80]

Re: Sun / Samsung 24" warmup issues

All the cables are properly seated?

yes.

the issue in question is something I've seen repeatedly even when it was in it's original position on the desk. So far other than that first power on from completely cold this time, I've seen no other hint of any more noise.

guessing my next test is to leave it powered off again for a couple of days and see how it behaves. Not sure -- at the moment it looks perfect.

[gerryg80]

Re: Sun / Samsung 24" warmup issues

Sounds like either a bad solder joint, or possibly bad caps on the main/logic board. Try heating up the power supply and/or the logic board with your blow dryer (yes, the same one you use for your hair) to see if you can shorten the time till you get a good display. Hopefully, you'll be able to isolate which board is causing the problem.

not sure if you read the whole intervening saga but my first attempt at repair I used standard caps that weren't low ESR. I suspect that was the reason it took a good hour to start working. Took me a couple of weeks to get the parts together then tonight with the proper caps in place the first power on displayed the original problem. Altogether it was plugged in for less than a minute so it definitely didn't get hot.

Came back to take pictures of the problem an hour later and so far it hasn't displayed even the slightest hint of any further problems.