[Boatanchors] URM25/E signal generators

[W4QG]

Hello All,

I recently acquired a fairly clean URM25/E signal generator.
It has what I understand to be a fairly common problem -
no modulation output. Carrier looks great - rock solid.

Anyway, I have been looking for any documentation on this signal
generator and have found basically nothing. Is the /E an uncommon variant? 

Does anyone out there in boatanchor land have any suggestions
as to where I might find a manual? Or some documentation detailing
the differences between the /E and /D or /F

Thanks!

73,

Paul W4QG