Commodore Pet 2001 Troubles

Dear Fellow Enthusiasts ... Firstly, I must admit to being somewhat of a 'lurker' here reading with great interest the postings and never failing to be amazed at the shear amount of amassed knowledge on the subject. My thanks to you all. Is there anyone here that can help me with a Commodore Pet problem that is really starting bug me !! It is a Pet 2001 32N with a Computhink Pet II Disk Controller Board and a pair of Dual Computhink drives (Model : DKH 642-I). The machine starts up just fine and you can enter DISKMON by typing SYS11*4096 However, upon entering commands like $LOD,1,"FOO" the screen turns to a complete screen full of small squares - chequer board style. Upon the command $DIR,1 the screen briefly displays a boarder around the screen where the directory content would normally appear and as soon as the drive activates the screen turns to chequer board. I have done the usual of re-seating the IC's, and I am hoping this isn't failed ROM. Another clue maybe that for some reason, when the drives are activated, BOTH drives activate together, which obviously they shouldnt. I haven't yet gone to the lengths of scoping the control lines but will start there tommorrow evening ... Does this sound like a problem that anyone has enountered before? Are there any 'Petsperts' out there that could help get this machine back on the road? Thanks in Anticipation Jason Fitzpatrick www.ComputingHistory.org.uk