Still worklng to try and get just one 5200 fully working, Bought two other for parts donors and now have the basic system working on all except one voltage range. The power amplifier in particular, is fragile and there is no current limiting, so if it goes down, there are low wattage sacrificial resistors on the psu pcb that burn out to protect other areas. Rebuilt the psu, low value resitrs on pcb pins, fitted heat sinks on a couple of transistors and fitted a fan, cross flow across the psu compartment. Some of the psu parts run too hot to touch and discolour the boards over time, tracks lift and as a design, a bit on the edge. Psu is fine now, but mine has the o/l led flashing at times, so the next step is go through the cal procedure as far as possible. If still issue, then dig deeper. According to the the manual, just about all the basic functionality can be checked out, range by range, with the power amp board removed and a jumper fitted, which might save some trouble. Afaics, the overload circuit shorts the input to the power amp on an anomaly, so if that's happening, the issue might be earlier in the chain. Fully direct coupled signal chain as well, ouch.
Run the zero offest calibration procedure on the power amp at least, as it is direct coupled to the output ratio transformers, which can burn out, making the whole thing scrap. Also, replace the two power amp 68K 2w comp resistors, which run quite hot, as they will blow the power amp if they fail with age and go oc. (mine did) Replaced with 2w metal oxide. Old, but a really good calibrator, with accuracies of a handful of microvolts when right, but Fluke were stretching the art at that time. As shown by things like the power amp bootstapping technique, to enable the use of high frequency, but low voltage and power (TO5 can) transistors in the output stage. +/- about 300 volts on the power amp, ~600v dc total, so be carefull where you stick probes and for your own safety. Good news is that the power amp uses sockets for most transistors, so you have to ask, why they did that. The schematics are amazing and not too difficult to work out what each board does. Very clever design for it's time.
Definately a keeper, if you can keep it alive :-)...