ID my ECU please
 

Pulled the ECU from my parts car to swap into Daniel's car to troubleshoot his problems and noticed that the RAM was socketed and had a handwritten sticker on it. This is different from Daniel's so we're wondering what the difference might be.
My parts car is 1992 JDM. I think Daniel's is the same.
A couple of photos are attached.

Inscription on the sticker is
F23AYD06

I've googled the number, but no hits.

Re: ID my ECU please
 

That is a TSB ROM that Subaru had installed at some point.

Re: ID my ECU please
 

How is the TSB ROM different from standard ?
Why would it have been replaced ?

Re: ID my ECU please
 

subaru issued new roms to correct drive ability and starting complaints. i believe that rom is to correct a rough start when cold symptom.

Re: ID my ECU please
 

Shane TSBs (Technical Service Builds) - were quite common in USA/Canada - less common in the rest of the world.

I remember seeing a complete listing here some years ago, along with explanations.... maybe someone can point to where they are to be found?.

Most TSBs were done free of charge - due to legal requirements relating to service or safety regulations.

Re: ID my ECU please
 

That looks like a USDM ECU (label D1 or M7), not a JDM (label D2).

The JDM ECU doesn't have the little daughterboard with the atmospheric pressure sensor on it. The TSB rom chip is typically only present on USDM vehicles.