emachines T6420 cooked caps on board?

[ZJChaser]

OK, just a quick introduction, I'm a networking guy, not an electrical guy. I have no problem with standard trouble shooting but generally draw the line when it comes to physical failures on the mobo. I figure this site will provide handy. I'm just confirming with your expertise that this board is likely smoked(not worth replacing the caps to the user)

EMachines T6420 that was apparently acting strange for a few days then shut off and wont post anymore. When you try to turn it on the fans kick on full speed and stay there then wont turn off until you pull the power cord but you dont get any post. With another Antec PSU the fans try to kick on but dont and nothing else happens. With a 2nd antec PSU nothing happens at all.

The stock PSU is a Bestec ATX-300-12e, do these tend to be as bad as the 250s at killing motherboards?

in this photo from the top, 2-5 all have bulged tops and #3 seems to have residue on top. Very small spec of residue on the top of 4 and 5 as well.
http://i12.photobucket.com/albums/a2...r/IMAG0011.jpg

My assumption is that they are toast and I'll be sending this one off to pasture

Thanks much.

[seanc]

Re: emachines T6420 cooked caps on board?

I can't give an advice about the Bestec 300w 12E, but I can tell you about those capacitors.

They are United Chemicon KZG, they do not like heat and often fail without visibly showing it, when they do show it, as in your case, it's obviously more useful.

The capacitors can be replaced with low ESR replacements and the board should work fine again, on the presumption that no other components have shorted. I've only come across one board where this had happened with KZG, at that point it was just easier to replace the board.

I just got done changing around 30 on a DFI lan party motherboard, POSTs first time, every time now. Still more smaller ones to do.

[shovenose]

Re: emachines T6420 cooked caps on board?

i have heard that the 300w 12e is a different design so its fine. but i have seen a 300w 12e with bad caps (teapo) so check the psu for cooked salami (erm excuse me capacitors) as well

[c_hegge]

Re: emachines T6420 cooked caps on board?

I think the ATX-300-12E is OK as far as the 5vsb is concerned. It has an entirely different circuit that is not vulnerable to overshoots. However, they still use caps which are junk and can fail.

Those Chemi-Con KZG caps on the motherboard look like 3300uF 6.3v. If that is the case, you could replace them with these.

[momaka]

Re: emachines T6420 cooked caps on board?

Bestec PSUs are okay except for the Bestec ATX-250 12E. Since yours isn't one of those, motherboard is likely fine and just needs a recap.

If you don't want to recap the motherboard and you live in the USA, you can recycle it by putting it up for free on your local Craigslist or Kijiji.

[ZJChaser]

Re: emachines T6420 cooked caps on board?

Well I've never done a cap replacement or soldering on circuit boards or small electronics but I figured this was a perfect opportunity to learn since its scrap anyway if I mess it up. I've already pulled the board and pulled the bad caps. I'll see if I can find some locally tomorrow and replace them.

You guys nailed it. They are indeed KZG 3300uF 6.3V, well done.

[shovenose]

Re: emachines T6420 cooked caps on board?

i would still suggest pulling the psu, opening it up, and checking it for bad caps. it wont hurt to check

[c_hegge]

Re: emachines T6420 cooked caps on board?

I'll see if I can find some locally tomorrow and replace them.

Local shops almost never sell appropriate caps. Use ONLY one of the following series:
Rubycon MBZ or MCZ
Nichicon HM or HN (as long as the date code is newer than 2005 - H05xx)
Sanyo/Suncon WG
Panasonic FJ or FL
Samxon GD or GC

Depending on the board, Panasonic FM might work. Their specs would be a slight downgrade form Chemi-Con KZG but might be close enough. Also, Panny FM would be 12.5mm diameter and might be a pain to squeeze in as the original caps are 10mm.

[PCBONEZ]

Re: emachines T6420 cooked caps on board?

i would still suggest pulling the psu, opening it up, and checking it for bad caps. it wont hurt to check

Yes

[PCBONEZ]

Re: emachines T6420 cooked caps on board?

Local shops almost never sell appropriate caps. Use ONLY one of the following series:
Rubycon MBZ or MCZ
Nichicon HM or HN (as long as the date code is newer than 2005 - H05xx)
Sanyo/Suncon WG
Panasonic FJ or FL
Samxon GD or GC

Depending on the board, Panasonic FM might work. Their specs would be a slight downgrade form Chemi-Con KZG but might be close enough. Also, Panny FM would be 12.5mm diameter and might be a pain to squeeze in as the original caps are 10mm.

Yes

[PCBONEZ]

Re: emachines T6420 cooked caps on board?

Well I've never done a cap replacement or soldering on circuit boards or small electronics but I figured this was a perfect opportunity to learn since its scrap anyway if I mess it up. I've already pulled the board and pulled the bad caps. I'll see if I can find some locally tomorrow and replace them.

You guys nailed it. They are indeed KZG 3300uF 6.3V, well done.

The only thing you will find really different about solding caps on mobos it that they are thick and have a ground plane.
[The ground plane is basically a grounded sheet of copper between the layers of the PCB. Most mobo caps will have one leg connected to it.]
- As a result the heat you apply gets sucked right out of the solder joint [and tip] so you need a heavier duty soldering iron than you do for most PCB work.
.
Too 'weak' of an iron [either by watts or recovery time] and you will find you are spending too long trying to heat joints and excessively heating the board. [And possibly burning off solder pads.] This is because the heat leaving the joint into the board is doing so faster than [or nearly as fast as] the iron is putting heat into the joint. [IOW you are slowly heating the -whole- board vs quickly heating just the joint.]
.
Some people [experienced or talented ones with 'the nack'] get by with 40 watts irons but most people find the sweet spot to be 50-60 watt irons.
I did my first passel of mobos with a 40 watt because that's what I had around and I didn't think a 50 watt would make that much difference, however, it does. On mobos there is definitley a noticable difference between using a 40 watt and a 50 watt iron. Between 50 and 60 watts, not so much.
.
Also irons with a cermamic heater [element] are better because they reheat [when touching iron to the joint cools the tip] much faster than the older wire-wound elements. [That is the recovery time.] A 50-watt wire wound will work fine with a tip that has some mass to it [the mass stores heat] but a 50-watt ceramic will get it done quicker, be a little easier to work with and you won't need a massy tip with a fat base to store heat.
.