Someone explain this? Emachines monitor

[mockingbird]

Re: Someone explain this? Emachines monitor

Ok, the caps that interest me are those on the bottom left near the two coils. You want to make sure that all those caps have the same ESR, because they're all part of either 1 or 2 pi filters.

Also, the starter cap near the big "KM" capacitor, did you change that as well?

I re-capped a Samsung 226bw, and I used too-varying ESR caps by a pi filter. It ruined the starter cap.

[shovenose]

Re: Someone explain this? Emachines monitor

I'll have to check the two letter code tomorrow but I had taken a pic of top of board (although with cell phone for now)

Yup, those are genuine. Panasonic's the only good cap manufacturer with that weird T top...

[caphair]

Re: Someone explain this? Emachines monitor

Ok, the caps that interest me are those on the bottom left near the two coils. You want to make sure that all those caps have the same ESR, because they're all part of either 1 or 2 pi filters.

Also, the starter cap near the big "KM" capacitor, did you change that as well?

I re-capped a Samsung 226bw, and I used too-varying ESR caps by a pi filter. It ruined the starter cap.

Initially there was only one bulged capacitor in the bottom left you're referring to, it was the single one between the two coils. I'm assuming they're all the same ESR since it was a kit of same brand?

The starter cap you're referring to, which would that be? Near the heatsink? If so, yes that was replaced as well.

Also, I partially reassembled monitor to see what would happen and of course, it powered up fine. Feeling more stumped now, as I'm sure problem will return again.

[PCBONEZ]

Re: Someone explain this? Emachines monitor

With an intermittent problem check for cold solder joints.
Especially on the larger components like the transformers.
.

[caphair]

Re: Someone explain this? Emachines monitor

With an intermittent problem check for cold solder joints.
Especially on the larger components like the transformers.
.

I have and resoldered some. With this board, all the solder has a dull/grey hazy surface. Would this be bad joints or use of lead free solder? It's just not shiny like I'm used to seeing.

[PCBONEZ]

Re: Someone explain this? Emachines monitor

Probably lead free, but it makes seeing cold joints more difficult.
It's also more prone to cold joints than leaded solder.
.
A magnifying glass or 'lil 'ole lady reading glasses from the dollar store can help see small details.
.

[mockingbird]

Re: Someone explain this? Emachines monitor

Initially there was only one bulged capacitor in the bottom left you're referring to, it was the single one between the two coils. I'm assuming they're all the same ESR since it was a kit of same brand?

Not necessarily, and this is a common mistake I see in these "repair kits". It is automatically assumed that if they're from the same series, the ESR will be identical. This is not true.

Sometimes you have to mix different series' to get the best result. You can also go a little higher with the voltage of a cap to get the desired ESR (Though I have absolutely no idea how a capacitor behaves ESR-wise if it is not used to its full potential. Does it just perform the same as it's lower-voltage sibling if only that voltage passes through it - perhaps PCBONEZ would care to elaborate). Look meticulously at the datasheets before you re-cap anything.

[caphair]

Re: Someone explain this? Emachines monitor

Probably lead free, but it makes seeing cold joints more difficult.
It's also more prone to cold joints than leaded solder.
.
A magnifying glass or 'lil 'ole lady reading glasses from the dollar store can help see small details.
.

Good tip I'll have to pick a pair up. Curious though, wouldn't cold solder joints act like an open circuit? (no power symptoms?) This problem is more like something shorts instantly cutting all power off.

I'm limited in my electronics knowledge but recently grown a high interest in learning, so please bare with me in my journey of troubleshooting. Btw thanks for all your input thus far.

[PCBONEZ]

Re: Someone explain this? Emachines monitor

Sometimes.

Other times it behaves more like a connector pin with too much corrosion.
Like cuts in and out.

Once in a while you will see one were the lead actually wiggles in the solder blob.
Other times they just look like cracks in the solder similar to one coat of paint over another.

Heat-up and cool-down [expansion/contraction of the lead] can affect them and make the connection come an go.
Also shock or vibration.

What happens is either the pad, the lead, or both don't get hot enough for the solder to bond even though the solder is hot enough to flow.

In mass produced stuff it's a problem to get it right every time with the automatic soldering machines they use.
They have to get all the solder everywhere hot enough without heating any components so hot they get damaged.
When they don't have it dialed in right you'll see problems with the bigger parts first.
.

[caphair]

Re: Someone explain this? Emachines monitor

So say there's a bad solder connection, would heat cause it to fail or momentarily work? I imagine since heat causes expansion the contacts would have a better chance of touching? I ask because maybe with it working I could use some cold air on different parts to see if it'll shut off or not.

[PCBONEZ]

Re: Someone explain this? Emachines monitor

So say there's a bad solder connection, would heat cause it to fail or momentarily work?

Either way.

I ask because maybe with it working I could use some cold air on different parts to see if it'll shut off or not.

Visual inspection or just resolder anything suspect.
.

[caphair]

Re: Someone explain this? Emachines monitor

Ok I'll take another look when I'm home. Also one thing to note, with power board only plugged in, measuring voltage at logic board connector labeled 12v and 5v I get readings of 11.58v and 5.05v. Seems good no? If I had a bad connection wouldn't measurements be off? Also these were measured when problem was occurring.

[PCBONEZ]

Re: Someone explain this? Emachines monitor

The voltages sound good but that's just power to the logic board.
You power board also has an inverter on it that has nothing to do with that and which has two transformers.
If the inverter is cutting out then the backlight will too so you won't see the image the logic board is sending.
.

[caphair]

Re: Someone explain this? Emachines monitor

The voltages sound good but that's just power to the logic board.
You power board also has an inverter on it that has nothing to do with that and which has two transformers.
If the inverter is cutting out then the backlight will too so you won't see the image the logic board is sending.
.

True. But I thought if there was an inverter/backlight problem usually monitor stays on just no image? Mine completely loses power even led until a power cycle.

[PCBONEZ]

Re: Someone explain this? Emachines monitor

If it completely loses power when the problem occurs then what you said in post 32 isn't true.

[Scenic]

Re: Someone explain this? Emachines monitor

*brainfart*

could the fault be on the main board..?
For example, if the voltage regulators on the mainboard (3.3V or whatever is needed by the IC) aren't working properly or work, but intermittantly, the result would be the same (sometimes it works, sometimes it's dead), no matter if the PSU works fine or not.

When the monitor plays dead again, check the output voltages of the PSU. If they're OK, but there's still no reaction whatsoever from the monitor, I'd take a look at the mainboard (or more specifically the one or two voltage regulators on there. Maybe even the caps too)

Pics would help

[PCBONEZ]

Re: Someone explain this? Emachines monitor

True. But I thought if there was an inverter/backlight problem usually monitor stays on just no image? Mine completely loses power even led until a power cycle.

No backlight = black screen [image or not]
Backlight on w/no image = white screen.
.

[caphair]

Re: Someone explain this? Emachines monitor

If it completely loses power when the problem occurs then what you said in post 32 isn't true.

Maybe if I had main board connected I wouldn't have had those voltage read outs? But that's what happens, monitor led comes on first followed by screen powering up as soon as Emachines logo appears power cuts out from LCD and led power light, pressing power button then does nothing at all.

could the fault be on the main board..?
For example, if the voltage regulators on the mainboard (3.3V or whatever is needed by the IC) aren't working properly or work, but intermittantly, the result would be the same (sometimes it works, sometimes it's dead), no matter if the PSU works fine or not.]

Hmm I didn't measure voltage regulators. But I rechecked underside of PSU today and noticed what could have been more cold solder joints so I fixed those, also on power button chip couple looked bad as well, touched those up too. For now the monitor is yet again working and I'm using it as I type. I'll keep you all posted on what happens and the longevity of it this time around. Thanks for all your input

[caphair]

Re: Someone explain this? Emachines monitor

Ok so problem is back yet again, this time only lasted couple days. I'll take better pics of mainboard and PSU tomorrow when I have time to disassemble it.

For now I've included a quick video to demonstrate exactly what happens. Maybe it'll be of some help.

This is right after a power cycle, it's non-responsive otherwise, pressing power button does nothing.

http://www.youtube.com/watch?v=NOwgX...ature=youtu.be

[Krankshaft]

Re: Someone explain this phenomenon? Emachines monitor

Confused now, I unplug from outlet and plug in the other pair of backlight wires, plug monitor in, turn on, and it has since then been working 100% perfectly. I'm using it now as I type. What's up with that? Anyone ever hear of this, know the explanation? Thanks!

It could be bad solder joints from the backlight wires to the CCFL. The inverter will shut down in a few seconds if it doesn't sense current flow through all of the CCFLs. Moving the connector and wires could have temporarily reseated the bad solder joint. Arcing from the bad joint could have been what destroyed the inverter semiconductors that were replaced as well.

A bad CCFL can also cause the inverter to shut down in this way the only way to verify that is to remove the CCFL enclosures and look at them during powerup to see which one isn't lighting. The less invasive way I use is to buy 4 CCFL case lights from e-bay. They come in nice rugged plastic enclosures so you don't break them. They're made for decoratively lighting computer cases.

If the inverter fires up with the known good CCFLs and stays on you know you have an issue with the CCFLs shutting it down.