7L5 early version (SN below B069999) Mod FB for 7854 compatibility

Cliff Carrie


I too have spent a lot of time on my 7L5, mostly in a complete overhaul of the front panel hardware bits and correcting some assembly errors from the last person who took it apart. This hobby is at least as much about restoring these classic units as it is about using them.

Thanks for the links to your earlier posts. I had read them some time ago.
I can certainly agree that the "below 10 kHz" problem could be in either the 7L5 or the 7854. I will try to test my 7L5 in a non-7854 7k mainframe. I have an acquaintance locally who had at least one.

There is a big difference between the two problems, however. In the 10 kHz problem, the 7l5 is correctly tuned. Only the frequency display is wrong. In the power on problem, the 7L5 is actually tuned to 3778 kHz instead of zero. I can't think of any signals inbound from the 7854 to the 7L5 that can change the tuning. I still hope there may be a 7L5 solution to this one. I will keep searching.


Nenad Filipovic

Hi Everybody,

Chance had it that most of the time I spent on my 7L5 went into fixing,
calibrating, adapting... rather than actual use. But this is about to
change as I'm (hopefully) done with all the upgrades and (at the moment)
fairly satisfied with the result.

I compiled a set of instructions on how to modify the older 7L5 for
compatibility with the 7854 mainframe and uploaded them to the group's file
section at:

Many of the issues covered apply to later 7L5s as well, so I suppose anyone
using a 7L5 in 7854 might be interested to read the document.

Of course, comments and suggestions are welcome.

Best Regards,
Nenad Filipovic