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Old 07-28-2010, 02:59 PM   #81
PCBONEZ
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Default Re: Dell GX620

Quote:
Originally Posted by speg_head
Would it be safe to say that 0.00 is a good reading if the capacitance reading on those caps are accurate?
That's a good sign but not enough to call it good.
The reason is the test signal from those is at 100kHz.
A standard Multi-meter uses a DC test signal.
You need to know what the cap is doing at DC.
-
You DON'T need a fancy or high accuracy meter for this.
You aren't looking for a specific number, just 'high' or 'low' as like a go/no go check.
A cheap $5 [or $2 at some places] would do fine.

An old style analog meter [one with a needle] is much easier to use for this check because the needle swings to one end or the other quickly and you don't have to wait for 5+ second on each cap for the digital numbers to stop changing. - No so much of a bother when you are only checking 3 or 4 caps but it gets OLD quick if you have more caps to do.

Note: When you check can't know the caps initial charge vs discharge condition. Even if you short the cap first there is some residual charge. Polarity of the leads doesn't matter but you do have to wait for charge-discharge of the cap to steady out if you have leads reversed from the caps actual condition. The DC test signal in the meter will charge the cap in the direction of the lead's polarity.
- If the cap [assuming a good one] is partially charged in the direction of the leads polarity then it will go high and stop [or slow WAY down]. That point is where the meter should read way high.
- If the cap [assuming a good one] needs to discharge then charge to match the leads then with an analog meter you will see it go low, might pause, then it will go way high and stop [or slow WAY down]. Once all the excitement is over you have your meter reading.
- With a digital meter all you will see is numbers flashing and you won't know where it is in the cycle [or if it's done] so you end up waiting longer for a steady reading. With an analog meter when you see the reading way high and the needle is slowing to a stop you can call it good without waiting for it to stop completely.
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Old 07-28-2010, 03:01 PM   #82
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Default Re: Dell GX620

You -are- checking with the caps out of circuit - right?
Checking caps that are in parallel doesn't work.....
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Old 07-30-2010, 01:33 AM   #83
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Default Re: Dell GX620

Yes I am testing all of the caps out of circuit. Im a bit confused with the multimeter test though. I have a digital one, not sure what setting to use to do the test. There is DCA, DCV, and a section labeled with an ohm sign. In each section are numbers ranging from 200m to 2000.

I tried setting it to 2000 in the ohm section and what the 2200uf capacitor shows are numbers that keep increasing to about 1900 , at that point it stops and goes back to default value of 1.

When doing a DCA test at the 2000u setting i get a 1 or 0 reading on the same cap.

If you can advise which test i should be doing would help,

Eddie
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Old 07-31-2010, 07:54 AM   #84
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Default Re: Dell GX620

You don't test amps, you test resistance.
A resistance meter sends current through the device under test and compares it to the current through a known [internal to the meter] resistance.

You are looking for a high resistance.
You are using the 2k-ohm [2,000 ohm scale] and it is over-ranging.
Mine flash all digits when over ranged but meters are different.
Try the 20k-ohm scale. [20,000 ohms] That works on most meters.

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Old 08-24-2010, 07:16 PM   #85
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Default Re: Dell GX620

Just posting a pic of my usff gx620 mobo. Had zero knowledge of caps before stubling across this forum. Was getting erratic usb mouse behavior and other complants. Finally the bsod occured with memory error noted. Replace with known good ram and got same bsod. Read this forum and help topic etc. and decided to pop the cover and found 6 bad 2200/6.3's. Ordered from here and then upon further reading noticed another culpret- 820/6.3 grrrrr.

Anyway I have notice the prior pics showed three different caps that seemed to be bad are now poly's as of 2007. Just thought I'd post a pic for anyone that cares.

Thanks all for helping us newbs not trash an expensive item instead of a quick fix (hopefully).
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Old 04-10-2011, 08:55 PM   #86
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Default Re: Dell GX620

Wow. Dell is a piece of work. Seems that the "replacement" motherboards that were sent out around 2009/2010 for the GX620's ONLY had the bulging caps replaced. It's funny to see a mix of Rubycon/Nichicon's of the same value on a motherboard and ever funnier to see the data code of the original Ruby MCZ's, because you KNOW they weren't replaced, and you KNOW the majority will fail RIGHT outside of the 5 year extended warranty mark. As for the boards sent out 4th quarter last year all the way until Janurary 2011, seems ALL the 2200uf, and rear 820uf caps are being replaced at the same time...the way it should have been done in the first place. Wonder what changed their tune?
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Old 10-04-2011, 10:59 AM   #87
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Default Darn Dell GX620 USFF boards

I've collected at least 12 bad GX620 lunch box USFF models at my organization over the past year. I've been wanting to replace the visually bad (vented) 6.3v 2200uF, 16v 1500uF and a few 6.3v 820uF that Iíve seen on these boards for 6 months. Lack of time to try my hand at de-soldering has kept me from doing this.

Anyone with suggestions for a de-soldering newbie, techniques, tools? I've seen a tool on Radio Shack site for a de-soldering iron 45W with a suction bulb. My solder wicker braid and 12W and 30W iron isnít working for me. I do have a digital meter but donít know how to use it. I had plan on popping the vented bad caps out and replacing them and cross my fingers.
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Old 10-04-2011, 11:46 AM   #88
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Default Re: Dell GX620

>> 45W with a suction bulb <<
Have one of those. - I hate it.
OTOH some people like them.
-
You need more watts for your iron. - Probably 50-60 watts is good.
Use that and the wick. Flux the wick if it isn't.
A big needle and something to hold it [I use an all metal exacto knife handle] helps to clear holes when they are stubborn after the cap is out.
-
For an occasional thing, Frys Electronics has a 60 watts pencil iron for $10-$15.

If this is something you will do often look for a Hakko 926 or 936 station with a 907 handle.
[926 and 936 are the same electrically and except for the base everything interchanges.]
What I did was got used bases on eBay then replaced the handles and got an assortment of tips.

There are certainly other options too.
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Old 10-05-2011, 12:57 AM   #89
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Default Re: Darn Dell GX620 USFF boards

Desoldering for 2 lead capacitors is unnecessary and only makes an easy job hard. The Dell boards are well designed and have good quality solder. Support the board in a padded bar clamp. Flux the cap solder fillets, heat alternately, and rock them out. Clear the holes with a 0.8mm drill in a pin vice. The sharp end of the drill hides inside the vice and the butt end sticks out to clear the holes.

Trim, flux, and solder in the replacement cap. Clean excess flux with a Q-tip and Brake Clean or Alcohol.

These items are widely available from many sources and you may already own some:
Flux: Radio Shack Rosin Paste Flux 64-022
0.8mm drill: Harbor Freight 30pc Mini Drill Set 94606
Pin Vice: General Tools - 92 from any hobby shop or hardware store
Bar Clamp: Harbor Freight 6" Ratchet Bar Clamp/Spreader 46806
Lead Trimmer: Harbor Freight 7" Wire Stripper with Cutter 98410

That style of flat blade stripper cutter will produce perfect lead cuts every time once you learn how. The Mini Drill set also contains 0.6mm drills which are necessary on some boards and fit in the General 92 Pin Vice.
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Old 02-16-2012, 03:09 PM   #90
Tekkamansol
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Default Re: Dell GX620

Hi I can really use some help I replace some bad capacitors on one of these gx 620 boards as training at work, I replaced five of them four 2200's and on 1800. Before the replacement the PC wouldn't even power on. No powers on no problem can access windows, though usb takes a bit of a while to be recognized and the major problem the PC won't shut down from windows. It will go through the process and just hang there. The mouse pointer can still be moved but screen is blank. It was my first replacement, any idea which cap I did wrong. Here is an image of the caps I replaced. Please not that isn't the actual board I worked on. Should I just start again and replace all of them.


Last edited by Tekkamansol; 02-16-2012 at 03:12 PM.. Reason: Needed to add more
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