Hi Bill,
I was very remiss in not reporting back to the group and thanking those who offered
advice. So I'm cc'ing the group - thank you all!
To answer your question, I worked backward from the amp outputs with a scope,
being careful to set tpwr appropriately since I don't have an attenuator. It
soon became evident that the output level from the high band VFS module was close
to zero even though the input from the refgen was normal and the low band was fine.
Since I'm reliably informed that one cause of this symptom is a failed harmonic
generator in the VFS, I swapped the cables on the two VFS modules to verify
that the module itself was bad.
After consulting with the faculty, it was decided that I would throw myself on the
mercy of Agilent in view of an electrical engineering background and having attended
Varian's 8 day hardware maintenance course.
It worked! They sold us the module without requiring that they come install it.
Our 400-MR has been running happily ever since.
If you're not seeing signals anywhere (but are still able to tune?), your issue
seems different. Power supply levels all look good? I'm at home right now
without access to my notes and docs but I could send you more details about
troubleshooting steps from the maintenance course later if that would be helpful.
-Steve
________________________________
> From: Hiscox, William <hiscox_at_wsu.edu>
> Sent: Tuesday, January 26, 2021 22:06
> To: Stephen Peurifoy <Stephen.Peurifoy_at_millersville.edu>
> Subject: Re: AMMRL: Varian 400-MR VFS repair options
Dear Stephen,
Was this problemresolved?
I was wondering, because our 400-MR went down suddenly, with no indication of
a developing problem. A user completed his work on one sample, changed samples,
and suddenly, there was no lock signal. I discovered that there was no signal
on any channel (however, I was able to tune the probe). I immediately suspected
a partial quench, because of a similar event, when the magnet quenched a couple
of months after the install. However, there was no loss of helium from the magnet
in this case, as had happened in the previous quench (~10-12% loss of helium
within 2 hours).
So, I was wondering how you proceeded with the troubleshooting, and how you
discovered the problem. I could not detect any signal from the instrument on an oscilloscope, except for the reference signal on the lock channel.
We have poured too much money into this console already, due to other problems,
so we have all but abandoned it. Any insight or relatable experience would
be greatly appreciated, however, in the interest of keeping this magnet alive.
Thanks,
Bill
----
William C. Hiscox, Ph.D., Assistant Director
Center for Nuclear Magnetic Resonance Spectroscopy
Washington State University
Pullman, WA 99164-4630
Ph. 509-335-8259
e-mail hiscox_at_wsu.edu
On 9/1/20, 12:17 PM, "Stephen Peurifoy" <Stephen.Peurifoy_at_millersville.edu> wrote:
Greetings spin doctors!
After being brought back up from a fairly lengthy
shutdown, our 400-MR has lost one of the channels
in its VFS unit. Note that this is the self-contained
AC powered version.
Agilent wants a lot of money for a replacement
channel module and an almost equal amount to come
install it which they won't let me do myself.
Does anyone have any experience with getting the
individual "bricks" in this thing repaired, either
in-house or by a third party? Or does anyone know
of a source that sells used/refurbished ones?
Thanks!
Steve Peurifoy
Chemistry Department
Millersville University of Pennsylvania
Millersville PA 17551
Received on Wed Jan 27 2021 - 05:36:29 MST