Well I've ended up rescuing another 180A, I always wanted to add the rack width version to my collection and found one recently in Germany, it's not in great condition but is quite an early one from the South Queensferry factory (U647-00149), the 1801A/1821A plug-ins are a little bit newer (must have got swapped at some point).
Powering it up resulted in not much happening, the beam find button did produce a spot on the CRT, but initial testing was quickly interrupted by smoke emerging from the 1821A timebase section.
Yesterday I had some time to look at it, first thing as always was to check the power supply rails (I removed the plug-ins), all were OK apart from the -12.6V rail, which was over 20V.
After checking the voltages around some of the transistors it became apparent the amplifier transistor Q412 was faulty, it was not turning Q409 off. Q412 was completely open circuit, the manual gives part no. 1854-0071 and the part fitted was marked MPS3391, I replaced it with a 2N3704 (pinout is different to the old part) and the -12.6V was now working & could now be adjusted.
The plastic cover for the fuses was missing, they helpfully left the screw in place though, I found a plastic draw divider that was good size to cover the fuses, it was drilled and fitted a couple of plastic spacers fitted to get the height correct.
Many of the missing screws from the frame & one of the PCB's have been replaced and I cut a piece of thin plastic sheet to replace the piece missing from the metal cover for the HV section.
David