Franc Zabkar wrote:

What is the function of the primary-secondary coupling capacitor (eg
http://tinyurl.com/ha435) in a SMPS?

To dump switching noise on the secondary side back to the nice low impedance of
the reservoir cap on the primary circuit.


I ask this because I suspect it may be the cause of a video "hum" issue.

Quite likely.


I have a new DVD player that gets along just fine with my 34cm TV but
produces severe hum in the picture of my 80cm TV. The same TV works
well with my other DVD player. I am considering removing the subject
cap from my TV (the DVD is under warranty), but I'd like to know if
there is any reason why I shouldn't. BTW, the TV is a gut-buster so
I'd rather not move it unless I have to.

FWIW, the symptom looks like common mode noise.

Yes it will do !

That cap is needed to conform with EMI regulations btw.

Graham