A Line Mechanic reports installing a non-RAAS rated GPWS computer into a Boeing aircraft modified for RAAS GPWS function. Maintenance Control later noted the aircraft was 'misconfigured' and grounded the airplane.

Narrative

A history of two GPWS faults led to inconclusive trouble shooting of the system. Maintenance Control advised; 'Start the trouble shooting process with a computer change.' So; a -222 GPWS computer was acquired from the [Stores] and installed; replacing a -224. The electronic maintenance log gave a message of 'improper part' but I determined the Illustrated Parts Catalog (IPC) effectivity allowed a -222 [GPWS computer] and overrode the warning.Flight crew wrote-up RAAS system inoperative (inop) and Mechanic B deferred the RAAS function as inoperative (inop). Flight departed as Mechanic C called to say he had the same issue several months earlier because the -222 has no RAAS function and therefore no RAAS callout during self-test. Mechanic B called Mechanic C to install -224 [computer] when aircraft transited his station due to concern of an incorrect MEL; but part replacement was not accomplished. Maintenance Control was then called and they called the aircraft 'misconfigured' and made it Dead on Arrival (DOA) where a -224 was installed.I; Mechanic B; and the flight crew missed the fact there was no RAAS callout when there should have been an 'inop' call out if RAAS was malfunctioning. I took the first EGPWS computer I found in [stores] and looked at the adjoining spaces for other [GPWS] part number (P/N) computers if we stocked them. Seeing none; I assumed we only had the -222 in stock; the -224 we stocked was one shelf down and on the end. The IPC had multiple Engineering Authorizations (EA) and Engineering Orders (EO) listed in the comments section that defined the software progression of the P/N changes for GPWS; there are four basic computer P/Ns.I did not look at these until after Mechanic C called. The EO that was referenced in the -224 comments is 41 pages long and requires quite a bit of reading to decipher. This is one of the most difficult 'effectivity' questions in the IPC I have run into. The information was there; I did not take the time to research it thoroughly. The missing RAAS callout was missed because it was not there. That should have been my clue that it was the wrong computer. The Captain was very sure we used the correct MEL; [which] provided pressure to use the incorrect MEL. Mechanic C had been working on a clarification of the IPC after his experience with the wrong P/N; but was not pursuing it currently. There were many breakdowns in this chain of events.