faulty IEC serial port on Flat NTSC C-128

Hi all,

I have a USA NTSC Flat C-128  STOCK:
This 128 powers up just fine, and it resets in all modes.
The problem is that all of my disk drives wont work with it,
it just pops up this error message:  DEVICE NOT FOUND ERROR?

I have run the C128 Diagnostic with the harness attached and it really
doesnt mention the
IEC serial port as not working etc.

The CIA chip for the IEC circuit tests okay
I replaced the TTL Logic Transeiver Bus chip, socketed it.
I replaced all of the IEC circuit I believe switching Diodes?
I replaced the IEC Din serial socket.

With all of that I still get the error message.
All I can figure is maybe i pulled pads or traces on the TTL Logic
Transiever chip.

  I just did purchase a good Oscilloscope and getting a crash course on how
to look for
high/low stuck bits etc and how to trace down a bad IC.

Other than that has anybody else ever had this failure?

BTW in the Diagnostic though the User port tested bad) since the Diagnostic
uses that cartridge in the user port.  So I cleaned the Edge connectors and
then it passed.

BTW I do have the C-128 Dead test and Diagnostic.
and I do have 2 different types of the harnesses, I cant recall the person
that made them, well one was made last year in Canada.

Terry Raymond