Switchmode Supply Troubleshooting tips needed.

Sep 03, 2006 3 Replies
J

Hi, I recently acquired a very nice portable spectrum analyzer that appears perfect, with one small problem. I've noticed, that over a period of 30min to 1 hr of 'on' time, I get a momentary situation which causes the switchmode supply to 'glitch'. The supply recovers very quickly ( a few milliseconds, max). This glitching is very sporadic, maybe once and hour or so. This is going to make it VERY difficult to track down. My initial thought was that there was a crt HV arc that is causing this, but I am almost wondering if the switchmode supply is dropping out of phase lock or something similar.



In any event, I could use some pointers as to how and attack this troubleshooting problem...



Any and all thoughts are welcome.. Jim WB5KYE


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J

look for bad electrolytic caps! mainly the large ones and bad solder joints that are heating up.

Real Programmers Do things like this. http://webpages.charter.net/jamie_5
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J

agree with this. for more information take a look at

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Jean-Yves.
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A

The supply recovers

Try tapping all over the unit with a screwdriver handle and see if the tapping triggers the glitch. That will point to a loose connection or bad solder joint somewhere. It's not unusual to find a joint that doesnt have any solder on it at all.

Other possibilities include a capacitor that shorts out periodically. The sawn-off deposited film ones do this quite often. Not a problem if they're used as power supply bypasses in a high-current circuit, but if they're used in a low-current place or bias circuit you'll see glitches. Also those little gumdrop tantalum caps do this.

You could also put it on a variac and try low and high voltage settings-- maybe one or the other will trigger it to fail more often.

As a last resort, try turning up the PS output voltage by 10% or so. That shouldnt hurt the good components, but often causes bad tantalums to short out completely. A bit crude but effective.

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