Defective RAM on Apple IIgs

["Bryan Parkoff" <nospam@nospam.com>]

Folks,

    I have experienced when I tried to copy files from DOS 3.3 to ProDOS 
using Copy II Plus 9.1.  I compared both files on source and target.  I have 
discovered that both are not identical.  I did notice garbage data from 
sector to sector.  I assure to be defective RAM built-in on motherboard of 
Apple IIgs (256KB).  I did diagnose using Ctrl-Open Apple-Closed 
Apple-Reset, but it shows, "System Good".  It does not make sense.  It 
should have scanned bank $0 through $3 to detect corrupted data in RAM.
    I have tested another Apple IIgs motherboard.  It is working fine when 
files are copied using Copy II Plus 9.1.  Maybe, I will need another 
software to test defective RAM.  If it determines errors in RAM. there 
should be a way to replace RAM chips on motherboard, but they are all 
soldered.  Any suggestions?

Bryan Parkoff