Switching power supply "tweeting"

[Ryan Underwood]

Hi,

What are the most common causes of a switchmode PSU that, after being off
for a good while and then powered on, would tweet once about every second
5-10 times and then eventually power on the unit successfully?
Furthermore, if I power off the unit and power it right back on, it comes
right back up. It is only after being left off for awhile that it
confuses its identity with a songbird.

Should I be looking for dried up caps, flaky semiconductors, burned coil,
or what? I'm leaning towards replacing the caps myself, but was curious
if there are general approaches to this problem.

thanks

 

[Mark D. Zacharias]

Just a guess, but I'd suspect one or more electrolytic caps, especially in
the primary side, 1uF at 200v, etc.

Caps on the secondary usually cause more regulation problems than startup
problems.

Mark Z.

 

[Ryan Underwood]

Just a guess, but I'd suspect one or more electrolytic caps, especially in
the primary side, 1uF at 200v, etc.

Caps on the secondary usually cause more regulation problems than startup
problems.

Thanks Mark. There were two 47uF at 250V; one was open and the other had
66 ohm ESR. I have a feeling that will turn out to be the problem!