On 16.07.14 11:08, Leonardo Marsaglia wrote:
> The other idea is to replace them blindly to take the chance and see if
> that solves the problem. It's a good possibility for the caps to be bad
> because the failure was coming and going.
Leonardo, one other thing worth checking as you go is all the solder
joints. A "dry joint" occurs if a component being soldered moves
slightly during the brief period when the solder alloy is pasty,
i.e. neither liquid nor fully solid. A fraction too little heat into the
joint is sometimes a factor, e.g. on heavy leads on a large component
amongst many fine components on a flow-soldered PCB. Such joints may
work fine for years, then fail in an intermittent fashion.
I remember encountering one which coincidentally was on a large
electrolytic capacitor. After years of use, I was able to pull the
component lead out of the joint by hand. That is unusual, as dry joints
normally appear solid, but rough¹ around the component lead. (In that
case, the lead may have become lightly oxidised during storage. Who
knows. I scraped it to bright metal before resoldering.)
If the unit is old, then replacing the electrolytics is a sound
investment in reliability. If that doesn't fix the problem, then
resoldering the other joints on the PCB _may_ do the trick.
After that, troubleshooting becomes trickier.
Erik
¹ Or, if unbelievably bad, the molten solder has not wetted the lead or
solder pad. Instead of flowing out over it, the solder sits in a blob,
barely making contact. That's more likely in inexperienced hand
soldering.
--
If you understand what you're doing, you're not learning anything.
- A. L.
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