yes you are right Kallikak, Larry Pina's book confirms that the errors are additive. This means he MAY have a problem with both chips at F5 & F6.
This may also be the computer expressing some other unrelated problem. The only reason I am still suspect is that I have always felt the RAM chips are pretty hardy in these old Macs and I can't for the life of me understand why two chips would just fail for no reason sitting in a box for 5 years, particularly in the absence of any physical evidence, like a dead bug, corrosion, or conductive material leaked on the logicboard.
However, one other thing to consider is that some part of the logicboard is making contact with the RF coating on the inside of the case. The 512K fixed that problem with a little rubber foot in the middle of the logicboard to keep that from happing and later models had a complete case bottom liner as well, rather than just the small socket RF shield of the originals.
With that in mind, have you tried starting the Mac without the rear case-bucket attached, sitting on a level non-conductive surface? That would certainly rule out that possibility.
This may also be the computer expressing some other unrelated problem. The only reason I am still suspect is that I have always felt the RAM chips are pretty hardy in these old Macs and I can't for the life of me understand why two chips would just fail for no reason sitting in a box for 5 years, particularly in the absence of any physical evidence, like a dead bug, corrosion, or conductive material leaked on the logicboard.
However, one other thing to consider is that some part of the logicboard is making contact with the RF coating on the inside of the case. The 512K fixed that problem with a little rubber foot in the middle of the logicboard to keep that from happing and later models had a complete case bottom liner as well, rather than just the small socket RF shield of the originals.
With that in mind, have you tried starting the Mac without the rear case-bucket attached, sitting on a level non-conductive surface? That would certainly rule out that possibility.