Try www.ebaman.com.
It contains a copy of the army version service manual, it is complete and a good scan.
You have to register to get access to the files, but it's free.
You will find it in the Test Equipment-> Tektronix-> Logic Analyzers section.
It's a direct copy from the original Tektronix service manual, complete with typographical errors, etc. that exist in the Tektronix service manual.
I'm curious as to the full symptoms of your 318 other than being unable to select 20nS clock rate.
I don't see how it could limit the clock sample rate, and not show some other indication that it thinks it's a 338, like incorrect setup menus such as the Setup menu being populated with 4 pods of signals (318 only populates Groups 1 & 2 w/ signal names for pods A & B, respectively). Or, not fail numerous tests of the hardware in respect to ACQ/Glitch capture SRAM. Either in the normal startup diagnostics, or any of the manual diagnostic tests.
Keep us posted on your progress.
Sbirdasn.
