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Old 09-24-2008, 07:48 PM   #1
powrslave007
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Default Failed Recap -New capacitor very hot to the touch

Hi all - I just attempted my 2nd recap - this time without success. I replaced a bad Rubycon MBZ 6.3v 1000u with a Rubycon MCZ 6.3v 820u (all I have at the moment) -at first I thought the recap was successful, but the PC soon rebooted and I can hear a slight crackling/popping sound coming from the motherboard. Has anyone seen something similar? The new cap got very hot to the touch and FAST - the PC was probably on for less than 1 minute.

FYI, the Motherboard I'm doing the recap on is a IBM Barbados 915G/GV

Thanks!
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Old 09-24-2008, 09:04 PM   #2
gdement
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Default Re: Failed Recap -New capacitor very hot to the touch

Make sure you didn't put it in backwards. Also look for shorts.
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Old 09-25-2008, 06:48 AM   #3
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Default Re: Failed Recap -New capacitor very hot to the touch

post a pic of the board and the area of this cap.
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Old 09-25-2008, 08:05 PM   #4
powrslave007
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Default Re: Failed Recap -New capacitor very hot to the touch

Here is a pic - the replacement Cap is in the middle - notice the black heatsink looking item placed close to this cap - it also gets VERY hot VERY fast. That area of the board appears to be slightly discolored - scorched? -
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Old 09-26-2008, 11:59 PM   #5
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Default Re: Failed Recap -New capacitor very hot to the touch

That FET (Q190?) below the cap is probably cooked (shorted), and the rail that is powered by that VRM may have had an overvoltage as a result. If that has happened, a lot of mobo components could have gone south (CPU, Northbridge, memory, ...). Just pray that the FET shorted to ground rather than from the input to inductor junction.

The only course is to replace the FET (maybe two FETs on that rail), check the inductor and replace if necessary, and try again. Look for shorts on every rail before powering up again. If you're lucky, only Vcore may have had an overvoltage - the CPU may have fried, but your Northbridge and Southbridge may have survived. If you're unlucky, lots of things may have fried.
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Old 10-04-2008, 11:52 AM   #6
bgavin
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Default Re: Failed Recap -New capacitor very hot to the touch

I see the coloration difference in the phot.

LG, how difficult is changing it out? Never done one, don't have the parts, but could probably scrounge off a dead board. Just curious
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Old 10-10-2008, 10:04 AM   #7
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Default Re: Failed Recap -New capacitor very hot to the touch

Replacing FETs soldered to large copper planes is painful, but it can be attempted with suitable tools - hot-air gun, some kind of metal stencils to protect adjacent plastics, and a pair of hemostats to dislodge the FET when the solder softens. It may not be worth the effort unless the rest of the board is believed to be functional.
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Old 10-13-2008, 05:01 PM   #8
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Default Re: Failed Recap -New capacitor very hot to the touch

I've done it with a Weller 140w heating the large pad and backing plate and a small iron heating the other pads. It takes two people and the person helping me was a bit drunk and we didn't have the proper grabber tools so the quality wasn't very good.
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Old 10-13-2008, 10:23 PM   #9
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Default Re: Failed Recap -New capacitor very hot to the touch

I imagine the overheating did not occur before you did the recap?

Perhaps you shorted something when you did the soldering?
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Old 12-13-2011, 02:25 PM   #10
wtimber
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Default Re: Failed Recap -New capacitor very hot to the touch

I have 10 of these systems with these failed boards, FRU 39J6196. I called IBM and they want $1866.00 for the replacement board FRU 41T3044. We have 32 more of these systems in service until they also fry. They are failing at a rate of about two a week now. I tried replacing the caps and had the same result as above. Has anyone replaced the FET on these boards yet?
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Old 12-13-2011, 03:08 PM   #11
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Default Re: Failed Recap -New capacitor very hot to the touch

In my experience those FETs aren't that hard to replace. All you need is a fat iron (60W plus) with a wide chisel tip, and a finer one.

With the fine iron heat the legs, use braid to get as much solder out as possible, and then carefully lift one leg at a time with a pair of tweezers or a small screwdriver. Then heat up the fat iron, keep it on the tab of the FET for 30 seconds or so, and push it a little. If the FET moves easily when you push on it with the iron then it means the solder has melted - just use a pair of pliers to grab it and lift it off the board.

To put a new one in just do the steps in reverse - align it, solder the legs first so that it doesn't move, then keep the big iron on the tab of the FET and push on it until you feel it sink into the solder. Lift the iron, let the board cool, and it's job done.
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Old 12-13-2011, 08:05 PM   #12
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Default Re: Failed Recap -New capacitor very hot to the touch

Also the magnet wire trick works too, just take some magnet wire (easily salvaged from an old transformer, its coated so it won't stick to the solder), wrap it thru in between the body and pins, heat up the pin and pull the wire. If you properly desoldered the pin with a wick first it should pop right loose. Then you can take your iron and work on removing the back pad.
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Old 12-15-2011, 12:46 AM   #13
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Default Re: Failed Recap -New capacitor very hot to the touch

watch out for reversed markings on your board.
look at other caps to see the marking.most have a half circle for neg but a few(asus,asrock,asus oem,)have it positive.
iirc some of these are asus oem.
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