this weekend I got the Rifa-replacments and put 6 of them in the external EMI filter (the plastic appendice on the right of the backside) and 2 of them in the output filter.

With the same setup as before (roughy 45-50 amps with low voltage) those "birdies" seemed to be less strong, even with the internal shield removed. See below. Apperantly, much of the signal I measured last time got out of the unit through the unprotected supply line.?

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Next I took a near-field probe from the box I got with the measurement receiver and connected it to the SA.?

I used an H-field probe (the ring) and an E-field probe (the sphere) and lookes for the loctations with the hightes signal.

For the magnetic field that is close to the transformer on the left side, for the electrical field its above (couldn't go between) the radiators.?

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With the internal shield replaced I repeated the measurements.?

To my surprise, I could not see any signal on the measurement receiver anymore. With the probes I still got signals, strongest at the front (magnetic) and on a hole on the top (electrical) above the radiators. Electrical field was roughly 10dB above noise level, magnetic field a bit stronger.?

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Then I put back the outer cabinet. That made the elctrical field signal disappear totally.?

The magnetic field could be captured at the same location on the front as before, ?but weaker - just above noise level.?

The signal on the SA has a 20kHz component and another one at roughly 150kHz. It looks as if the 20kHz are modulated on the 150kHz.

A superficial study of the service manual reveals 20kHz correspond to the "pulse width modulator". There is also a 320kHz clock and other derived pulses of shorter duration than the 20kHz clock. These may lead to the 150kHz I've noticed on the SA. Perhaps this frequency depends on load conditions. I forgot to test before putting everything back...

What do you think?

cheers

Martin