Missing IC in Advantest R3261A Spectrum Analyzer

[sherlock]

I've been working on my R3261A spectrum analyzer and have run into a difference in the service manual and the actual equipment.  On the IF portion of the motherboard there's a section that has an input jack J3 and an output jack J4.  The schematic shows at the end of the amplifier chain U28 feeding U29, and U29 going to J4.  Well there's no U29 that I can find anywhere!  Tracing the connections shows J4 connecting to U28, which is clearly labeled on the PCB.  There's a picture of the board in the manual but that section is covered by a shield box so you can't see anything inside where U28 (and 29?) are.  I can see the Advantest numbers for the motherboard in the picture and they match exactly with the board that I have so the circuits should match.  There's no "unused" parts on the board either.  It appears that U29 may have been added at a later time but I'd guess that the PCB would have a different number on it.  There's also no mention in the manual of this part being added.  Has anyone that's familiar with this analyzer seen this or know where U29 might reside?  Thanks in advance...

sherlock