I recently bought three (!) HP 8594E.
They all arrived in working state, but:
Unit #1: PSU failed after 30 minutes
Unit #2: PSU failed after 2 minutes
Unit #3: PSU failed after 10 minutes and I think something on the motherboard failed, as well
I thought that it would be easy to get at least one working PSU out of the three, but I was wrong. After weeks of measuring, comparing exchanging parts and asking a friend for help, I gave up.
Managed to buy one good PSU, so I have now Unit #1 working.
Unit #2 was not working correctly, because someone disconnected two cables inside. After reconnecting them, the unit passes self-test and works OK. Using the 4th PSU, of course.
So now I am in need of another PSU, which is taking longer than I imagined. Ebay had a few on sale, but the asking price is about as much as what I paid for the three units!
I replaced the backup battery on Unit #1 and #2. Unit #3 is an older model with a different battery, so I did not change it for now, but I managed to make pictures of all settings, before it broke.
Conclusion: 250 US$ is a great price, but by all means try to buy two units, so that you have replacement parts! Even when the unit is working at the day you buy it, chances are that some electrolytic blows up after a few hours of use and without proper documentation or replacement parts, you are screwed...
Also, never underestimate the repair of a HPAK power supply. It can be just a blown resistor, but in my experience these PSU's are REALLY complicated with TONS of componentes, some probably unobtainable. If you are not specialized in repairing them, you will hardly succeed.
Conclusion: These older ancors are nice, but you should get more than one, so you can maintain them. One single replacement part will cost you as much as the whole unit, if not more. I could sell my spare units as they are, with broken PSU, and probably get more money than I paid for them, if not just for the YIG, which I know is working OK. I am saying this to put your deal into perspective.
Another example: I own a total of 3x R&S CRTU and 2x R&S CMU200. They are hardware compatible to a large extend. From those, only one CRTU is not working OK (bad RXTX board and lacks one other board). Why do I have so many? Bought them all as broken and repaired them. What started to be as a bunch of replacement part units, ended up to be repairable except one. Total cost: half of the price of a working unit.
This takes a lot of patientence!
Final advise: It is OK to buy such a unit, when you are sure you can sell it for the same or higher price. Beware of TEA and hording...
Regards,
Vitor