I've worked on quite a few E8285A, 8935 (E6380 & E6381) & 8924E/C over the years. PSU / Regulator board CAPS are the most prolific failures. CRT/Plasma displays next. Several have had failed measurement units (A19 in 8920). In the same one, Sig Gen Synth A14 had a tantalum cap pop on one of the DC rails. So I replaced all tants in its A19 but it still failed to calibrate. Swapped it out in the end. I've got around 4 dud A19s in the parts box. Another common error is out of lock OO LEDs illuminating which normally is a sure sign something is up with the 40V PSU rail. they are a great analyzer for general analogue radio. The only other I'd ever get would be IFR1900. From same era, does the same things but goes about it quite differently..
Chris, ZL1CVD