HP 9845 C with 280 option startup failure

I recently acquired a HP 9845C option 280 (was looking for it for a really long time). The machine is in an overall good condition, however it hangs during memory test ("MEMORY TEST IN PROGRESS"), even after cleaning all board connectors, resocketing all ROMs & repeated control-stop's. Before entering nirvana the printer outputs a couple of memory addresses. Although lots of defects may be responsible, I assume there is a combination of both a bad RAM chip and a ROM failure, since a RAM defect alone should (?) not crash the system during the test. The printout looks like this: 000000 100112 052525 000000 110112 052525 000000 120112 052525 000000 130112 052525 I guess the first number is the block ID, the next is the memory address within the block, and the last number is the test pattern, each in octal representation. Does anyone have an idea - how to really interpret the memory test printouts and - how to check the ROMs for bad data? Maybe there is anyone out there who did the job to read out the contents of his 9845 ROMs (they are all in sockets) for a direct comparison. There is a 98407A memory option installed, and, of course, a bit slice LPU. So the ROMs work out as: PPU assembly: CE1 LB: 1818-1591B CE1 UB: 1818-1592B CE2 LB: 1818-0846D CE2 UB: 1818-0841D CE3 LB: 1818-0837D CE3 UB: 1818-0833D CE4 LB: 1818-1898A CE4 UB: 1818-1899A LPU assembly: CE1 LB: 1818-1506A CE1 UB: 1818-1502A CE2 LB: 1818-1507A CE2 UB: 1818-1503A CE3 LB: 1818-1508A CE3 UB: 1818-1504D CE4 LB: 1818-1509A CE4 UB: 1818-1505A Most of them schould be the same as in an 9845B model 200 system. Thanks for your help Ansgar