Switchmode Supply Troubleshooting tips needed.

[Jim Flanagan]

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

 

[Jamie]

Jim Flanagan wrote:

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
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

 

[Jean-Yves]

In article <1UqKg.48$K84.44@newsfe03.lga>,
Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

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

agree with this.
for more information take a look at
http://www.repairfaq.org/sam/smpsfaq.htm

--
Jean-Yves.

 

[Ancient_Hacker]

Jim Flanagan wrote:

The supply recovers

very quickly ( a few milliseconds, max). This glitching
is very sporadic, maybe once and hour or so.

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.