If you run the self test enough times, it may give you a reference designation of the at-fault chip IE U413.
Keep in mind that the DMUX chips for each channel are not consecutive. From the edge of the board where all the high density connectors are, it goes CH3, CH4, CH1, CH2. So you'll be working the banks nearest to the 4 coax cables from the rear panel. I've had some of these scopes with multiple bad 1Mb chips! I usually replace 4 at a time then test again.
Here are some experiments I did on a 2M enabled scope on CH2:
CH2: shorting *WE on each bank:
component side of board.
U405: "WED JUL 13 12:51:08 2016 ERROR: diagnostic test failure, digDataFormatDiag, ERROR!!BYTE mode, in demux 198 ,i= 4 memBaseAdr 0x730000a= data = ffffb500, expectedData[i] = aa00";""
U413: "WED JUL 13 09:28:51 2016 ERROR: diagnostic test failure, digDataFormatDiag, ERROR!!BYTE mode, in demux 198 ,i= 12 memBaseAdr 0x730001a= data = ffffa500, expectedData[i] = ff00";""
Now solder side of board:
U409: "WED JUL 13 09:42:06 2016 ERROR: diagnostic test failure, digDataFormatDiag, ERROR!!BYTE mode, in demux 198 ,i= 8 memBaseAdr 0x7300012= data = 1a00, expectedData[i] = ff00";""
U401: "WED JUL 13 09:39:35 2016 ERROR: diagnostic test failure, digDataFormatDiag, ERROR!!BYTE mode, in demux 198 ,i= 0 memBaseAdr 0x7300002= data = ffffc400, expectedData[i] = 0";""
CH2 experiments:
NOTE: References to DAT[x] are the pinouts from the chip datasheet.
The Data lines on the top two banks are in parallel.
Tied DAT3 (U413 –17) on comp. Side of board to +5:
"WED JUL 13 12:35:20 2016 ERROR: diagnostic test failure, digDataFormatDiag, ERROR!!BYTE mode, in demux 198 ,i= 20 memBaseAdr 0x730002a= data = 3c00, expectedData[i] = 3400";""
Tied DAT3 (U414 –17) on comp. Side of board to +5:
"WED JUL 13 12:39:41 2016 ERROR: diagnostic test failure, digDataFormatDiag, ERROR!!BYTE mode, in demux 198 ,i= 21 memBaseAdr 0x730002c= data = 1a00, expectedData[i] = 1200";""
Tied DAT3 (U415 –17) on comp. Side of board to +5:
"WED JUL 13 12:41:23 2016 ERROR: diagnostic test failure, digDataFormatDiag, ERROR!!BYTE mode, in demux 198 ,i= 6 memBaseAdr 0x730000e= data = 5d00, expectedData[i] = 5500";""
Tied DAT3 (U416 –17) on comp. Side of board to +5:
"WED JUL 13 12:45:34 2016 ERROR: diagnostic test failure, digDataFormatDiag, ERROR!!BYTE mode, in demux 198 ,i= 7 memBaseAdr 0x7300010= data = 5d00, expectedData[i] = 5500";""
