[Premium-Rx] R&S ESM 500 display issues

[John Miles]

FYI, it looks like Rohde & Schwarz built at least a few ESM 500A receivers
without a couple of bypass capacitors on the CRT socket that are needed to
prevent a noisy or "dotted" display trace on the built-in panadaptor.  These
capacitors are shown in my service manual's schematic, but were not
installed in my '500A.  Without them, the display ends up
intensity-modulated by the 20 kHz CRT power supply, resulting in a
broken/dotted display trace on fast-rising vertical edges.

Maybe it was just my radio that was built this way, but if yours has a
similar problem, here's the solution (for the benefit of the archives):

- Install C22 (330 pF 1kV disc ceramic) between CRT socket pins 9 and 11
- Install C23 (0.01 uF 1kV disc ceramic) between pins 2 and 3

Easy fix, big display-quality improvement.

-- john, KE5FX