[time-nuts] Help with my FTS4050...

[Bill Hawkins]

Have you checked the power supply voltages?

Bill Hawkins


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of Chuck Harris
Sent: Saturday, January 08, 2005 9:01 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Help with my FTS4050...


Well, I dragged my FTS 4050 off of the shelf, and back to the bench
to see what was left of it.  It hadn't been turned on since it quit
in 1995.  It powered up ok, and the ovens stabilized at the proper
values, and the beam current returned to where it was when things were
normal.  It still won't lock, and the control voltage is stuck at 3.5V
which I am pretty sure is its attempt to pull the OCXO up in frequency.
The OCXO voltage control pot is fully CCW, and the frequency out is
just a tiny bit below 5 MHz... All consistent with an OCXO that has
exceeded its adjustment range for aging drift.

Ok, so what to do?  The only manual I have is an operation and alignment
manual for the FTS5000/100 module that is the guts of the 4050 frame,
and it talks about selecting a resistor: A4R64 to bring the DAC back
to the center of its range.  It has a table that says the nominal
value is 14.7K, and for a unit that has its control voltage at 3.5V,
I should replace A4R64 with an 8K resistor.  The only problem is I don't
have the schematics/drawings book for the module, so I have no idea
which resistor is A4R64.  They say it is mounted on a "bifurcated" terminal,
but there are no such terminals on the DAC (A4) board.

I think the C-Beam tube is working fine, as when I put a
Zeeman frequency of 42.820KHz, 1Vrms into the Zeeman port, the beam
current goes into a fairly deep dip, and both the amplitude and
frequency of the Zeeman signal change the dip's depth, and so does
the thumbwheel switches (though very slightly).

I suspect that all this source needs to be back up and running is
for me to adjust the OCXO to a new center frequency.  I remember
trying to do this back 10 years ago when it first quit, and finding
that the oven has no external adjustments.  I also recall that the
guts of the oven are stuffed into a vacuum bottle, and it looked
really scary to try and disassemble the unit.

Any ideas??

Thanks!

-Chuck Harris