Re: Yet another 7L5 issue (7L5 / 7854) below 10 kHz

Nenad Filipovic
 

Hi Cliff,

Yes, in my opinion the "below 10 kHz" problem is purely on the 7854 side,
as my 7L5 displays CF correctly in both 7633 and 7104. I did not bother
much with it as I simply got used to it, and with GPIB data it is possible
to implement a fix for it in capturing software.

The reset anomaly is also present in mainframes other than 7854. In my 7854
it powers up at 3778kHz most of the time, but not always. In 7104 it does
1788kHz or something similar. I did not get into it deeper as it did not
bother me nearly enough as the very annoying mV issue in LIN mode on 7854.
The last is definitely a 7854 fault.

Is your 7L5 the older (SN below B069999) or the newer version? Mine is the
older. I think I remember I read somewhere that the older version is prone
to the reset problem, but can't say for sure.

Best Regards,
Nenad

On Sun, Dec 8, 2019 at 5:34 PM Cliff Carrie <cliffcarrie@...> wrote:

Nenad,

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.

Cliff

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