Bad bad capacitors

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gz_24
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Post by gz_24 »

PDT_Armataz_01_40 :wav:
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evasive
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Post by evasive »

OK, here we go.

It seems a considerable number of Antec PSU's were made using fujiyuu and taepo capacitors. Quite a few of them are dying of badcaps now, as we speak. Be warned.
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Post by dve83 »

The following board has gone wonky due to bad caps: Going to replace them soon.

Soltek SL-85MIV3
Bad Caps: 10 x 6.3V 1000uF

Recently Repleaced Caps and running like a dream :-)
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evasive
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Post by evasive »

Soltek could have told you. All of them since 2001/2002. Good to see you revived another board though :)
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Post by AmEv »

Something I have learned how to do with a voltohmmeter.
If you have a cap that you think is faulty, but shows no physical problems (doesn't bulge or stink), then this is what you need to do.

For most accurate results, you need to remove the cap from the board. Put it into resistance mode. Put each probe onto one end (polarity isn't relevant right now). Resistance should slowly climb from 0 to infinity. Reverse and repeat.

The signs that it is a crapcap:

Resistance doesn't go from beginning to end
Rate is different when switched
Stuck on 0 or infinite resistance

Unnecessary to use VOM obvious signs are there. :roll:
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Post by Karlsweldt »

It is no simple matter to check capacitors for being good/bad. What is used is a special tester, which applies a set voltage and load, then checks the drop curve according to a reference. But it can only be done out-of-circuit. For in-circuit testing, a very expensive test instrument is needed.
An easier and equally effective method is to use a 6 volt AC source and lamp of about 250 mA with the capacitor in series with one lamp lead. Monitor the voltage on the lamp terminals. If no light, the capacitor is "open". If full voltage, the capacitor is "shorted". If half-voltage, then consider the cap as useful. This works with caps from 10 mfd to about 200 mfd. For larger caps over 500 mfd, use a doubling of lamp current. With caps above 1000 mfd, a lamp load of about 1 amp is safe. As long as the cap's voltage is higher than what voltage is used, no worry about accidents.
The cap acts as a diode would, passing only one part of the sine wave. The other half is blocked.

The motors that use capacitors for start/run use this effect to alter the phase relation of the incoming current to provide rotational force to the armature. But they are really two DC capacitors, back-to-back. No polarity!
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Post by AmEv »

OK, I know it says on the site, don't use "coldheat" type irons.
What about Weller iron? The ColdHeat requires a short to work. With this one, I have melted plastics. Is it safe to use on boards?
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Post by evasive »

The boards were soaked in hot solder when produced so the material can have some heat.

Is that Weller temperature-controlled?
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Post by Karlsweldt »

Those "cold heat" soldering irons use a low voltage, normally less than 3 volts.. but high current. For most components, there may be no worry about foreign voltage input. But for coils and shunts, there may be problems. And with those "cold heat" irons, you heat only the contact area.. and possibly not the component lead, which can create a cold solder joint!
I will stick with my Weller high-heat for most jobs, and use a pencil iron for when needed. At least you get contact on all connections for faster, safer soldering work. The larger the contact pad or component, the more heat you need to apply very quickly so as to create a proper melt on the solder joint. Smaller irons may cause excessive heat to gravitate elsewhere, until the proper melt temperature is reached.
The best soldering tool is the RF type, with paste solder. Just brush it on, aim the "gun" at the joint.. and 5 seconds later, perfect. But who can afford such an expensive tool?
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Post by AmEv »

evasive wrote:Is that Weller temperature-controlled?
Ah, yes and no. It has a 1 and 2 spot. It uses 4 AA batteries. However, it barely gets hot enough to produce liquid solder -- and that's with fresh, out-of-the-box KS batteries and in 2 mode!

I admit to have accidentally singed myself a couple of times. :oops:
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