So far I was not able to get good contacts with my PLCC socket. I just get signals on the pins when I push the socket down. 
Will try the smd version, if I will be able to solder it, which looks quite challenging to me...
How many pins from U199 one needs to electrically access and routed to the FPGA ?
There are total of 4x11 so 44 pins but what is the layout (position), which pins are actually necessary ?
Maybe quick picture or local layout to help visualize the density to be managed ?
You need 22 signals (plus ground although you could get that elsewhere).
The SMT socket from Methode (p/n 213044601) is the only socket I found that works without modification, although it just barely works. It will lock down onto the ramdac chip with a bit of fiddling with it, and contacts all the pins, but it pops back off rather easily in my opinion.
No other SMT socket I tried even came close to working.
Of the several through-hole sockets I tried, none worked without modification. They would not make contact with all the pins unless you pressed on them. The modifications involved removing some of the plastic at the bottom of the socket so that it would fit down onto the ramdac chip further.
The easiest one to modify is the ASSMAN A-CCS 044-G-T (DigiKey pp/n AE10064). On it, you can just use a sharp knife to cut away four little posts on the bottom of the socket. That let it fit onto the chip and make contact, but again, just barely. So I also removed each individual contact (pretty easy to do) and re-shaped the contacts so that it made better contact at the top of the socket. Sanding the top edge of the socket off a little also helps. I'm attaching a picture of before/after. It works well after the mods.
I prefer the Methode p/n 213044401 through hole socket although it is harder to modify. You need a milling machine or at least a dremel with steady hands to remove the plastic from the bottom of the socket. But the contacts can be removed all at once and re-shaped in a row. I found that easier than the one at a time ASSMAN contacts.
Either one might work with just removing the plastic at the bottom (without re-shaping the contacts), but definitely better after re-shaping the contacts.
Edit: On my TDS524A, there are a few small SMD resistors that sit very close to the ramdac so that I also needed to file a little plastic on one edge of the sockets to avoid hitting them.
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