How to identify faulty or Fake (Duplicate) ICs?
It's unlikely your part is counterfeit, especially if you purchased it from a reputable distributor. Have you verified the following from this datasheet:


Is your P1.26/RTCK pin pulled low? After reset the LPC2138 will sample the RTCK pin and if this is low the JTAG pins will be used as JTAG, otherwise they will be used as GPIO pins. (Page 12)
The P0.31 pin MUST NOT be externally pulled LOW when RESET pin is LOW or 
the JTAG port will be disabled. (Page 11)



  Reset pin is high.


How is your RESET pin pulled high, what value resistor? 



Detecting Counterfeits

There are companies you can send a part to and have it tested, American Counterfeit Detection is one such company.

Some of the signs to look for are:


Misspellings on the manufacturers labels
Scratches or sanding marks
Verification that the date code on the label match dates codes on the parts
Date codes that are not possible. ex. 0657
Date codes that are in the future
If parts are moisture sensitive they require a dry pack and a Humidity indicator card. Often the counterfeiters forget some piece of the moisture sensitive parts requirements.


This is a great resource for identifying counterfeit parts by visual inspection: Detection of Counterfeit Electronic Components

The following pictures show chips that have been sanded. Normally when a chip is molded it will not have any scratch marks.



Here you can see a marking that is easily wiped off.



Here you can see that they have attempted to re-stamp over the existing stamp. 



Aside from a external visual inspection, here are some other methods used:


Functional Testing
X-Ray, X-RF, or SAM Inspection
Decapsulation
Hermetically Sealed Electronic Component Leak Detection


Integra Counterfeit IC Detection Methods: