THIS. If it worked before your work on U8 and now it doesn't work after your work on U8 and that was the ONLY thing you did then that is cause.

Buzzing top to bottom and side to side (adjacent) is not enough. The 28 pads on U8 do not connect to a single point. Without branching from a trace there are FOUR potential branches from a pin/pad. Up from the pad on the front of the board, down from the pad on the front of the board, up from the pad on the back of the board and down from pad on the back of the board. That also requires that the through hole connects the pad on the front of the board to the pad on the back of the board.

If you buzz for continuity on the pad from the front to the back that does not take into account the trace leading away from the pad. It only tests the continuity of the through hole.

Most of the connections on U8 are part of a bus so if you really want to check for continuity of the bus test the points that do *NOT* include U8. That way you know that continuity through the pads of U8 are correct. If there is a break noticed then you can test the pad on U8 to isolate if the through is damaged.

I would be willing to be you have a broken trace coming off a pad - either on the front or the back of the board (more likely the front as it is concealed by the socket you put in place). Testing for continuity will reveal the break. You can fix the break using a jumper or if you want to see the break you will have to remove the socket. Removing the socket will risk further damage. You aren't the first person who has done this (I am guilty of having done this several times) and you won't be the last. There's another System 11 thread where someone did the same thing. Changed U25 (SRAM) and now doesn't have a boot. It's the same thing. Broken trace. It ALWAYS is. The odds of having a bad "new" part is low. Very low. The odds of damage to the PCB is high. Very high.

If you want a visual guide I have attached some images that might help. Good luck. Finding it is tedious but finding it is also rewarding.

01_U08_data_bus.jpg

02_U08_address_bus0.jpg

03_U08_address_bus1.jpg

04_U08_local.jpg

This is why installing NVRAM (by removing the SRAM and installing a socket) is rated as HARD for WPC. I have had friends deliver boards to me to repair because they gave up figuring out what they did wrong (i.e. which traces, pads or through holes they damaged or removed). I don't bother figuring out what they did wrong either. I just remove the socket they installed and inspect everything.

I realize that learning how to desolder has to start somewhere but I would never recommend anyone learn on this board. The exception to this is if an experienced person is supervising or monitoring the progress.

If salvaging the original SRAM is not desired then an alternative that I do recommend is cutting the legs of the IC (as close to the body as possible) and removing the body. Proceed to removing each individual leg by heating the pad and using needle nose pilers to remove each leg. This removes most every possibility of damage to the pads and through holes. Of course ... that recommendation is too late for this scenario.