In an old Spaceflight article I have found a mention of a test to be made by Voyager 1 in late 1986 to use the antenna as a sunshade to take pictures very close to the Sun. The idea was that if tests were successful, Voyager 1 could be used to image dust structures discovered in the infrared range by IRAS a few years before.
Anybody knows the results of the test (except that, of course if paved the way for the solar system portrait)?

I suspect it didn't work, suspect that the signal-to-noise wasn't good enough for zodiacal dust band imaging. The solar system portrait was taken with the sun visible, which accounts for the lens flare line of light that the "pale blue dot" was embedded (rather dramatically) in.

I have asked about this experiment to Brad Smith (the Voyager camera PI) and this is what he told me:
"The observation was Carolyn Porco's idea. We turned the spacecraft to use the High Gain Antenna to image the IRAS dust bands, probably in 1987. It didn't work as well as we had hoped because something on the spacecraft was still illuminated and had reflected light onto the back of the HGA so that part of each image was over-exposed. A portion of each image was still OK and Carolyn was able to get some results on particle size. I'm not sure, but I don't think she ever published her results."