Vintage Synth Repair

I have a Wurlitzer 4520 (the theater horseshoe version of the 4500 
series) which has one or more problems in the lower manual keying 
circuit(s). The Melodia voice is dead from C# (key #38) upwards 
which also affects the chime voicing and the Pizzacato and Bongo 
percussion signals. I was told by a Wurly tech to look at "the 
coupling capacitors on the lower manual keying circuit box" but I 
have no idea which caps he's referring to. He's in Missisippi and 
I'm in Ohio so it's not like he can come over and have a look. I 
have complete schematics for the organ and some limited experience 
in organ repairs. I would like to talk this out with anyone who 
might be more knowledgeable with this type problem so I can get this 
magnificient instrument back in full operation. Thanks in advance!!