In my experience, a cracked or broken probe insert is the commonest cause of
probe tuning changes. A useful tool for checking on the condition of the
inserts and coils is a borescope/endoscope camera. I have one with a 3.9 mm
camera end that can go directly into a 5 mm probe, or if desired, go into
a 5 mm NMR tube if you are concerned about scratching the inserts with the
camera end itself. These cameras are readily available for under $100. They
are also useful for checking if sudden shim changes are resulting from someone
breaking a sample inside the probe, and not thinking that is important
enough to mention to staff.
Two caveats with these inexpensive cameras:
-the business ends are ferromagnetic, making them not suitable for checking
out a probe while it is inside the magnet.
-labeling this product as an endoscope seems to endorse DIY internal medicine.
This may not be a good idea. At the least, they are inexpensive enough that
it would not be necessary to use the same camera for NMR probes, and non-
NMR applications.
Sending the probe back to the vendor's probe shop is by far the best way to
get it back to like new condition, regardless of the cause. (I was very sorry
to hear that JS Research had exited the probe repair business, as I got several
top notch repairs done through them.) At least some Bruker room temperature
probes have free standing coils that are not held to the insert by adhesive,
such that the insert can potentially be repaired in the field. I did that a
number of times in my old job, but have not had any broken inserts on Bruker
probes in my current job. I have had several broken Varian probes, where the
coils are glued on to the inserts, and I don't feel at all confident that I
could repair those anywhere near well enough to make the lineshape spec. Nearly
all of my broken Varian probes have been on instruments that do not have sample
changers. All of my current Bruker spectrometers have sample changers. I don't
think I have enough incidents to make for objectively reliable statistics, but
my definite impression is that sample changers handle tubes more safely than
the rotating crew of grad students and postdocs.
________________________________
From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> on behalf of PLscientific<pavel_at_plscientific.se>
Sent: Wednesday, August 2, 2023 7:20 AM
To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
Subject: Re: [AMMRL] tuning range shifts on BBFO probe
Hi Zdenek,
I would bid on the aging of some of the plate capacitors embedded in RF coil
construction or chip capacitor in the RF circuit. The cleaning of RF coil may
help in the first case, but usually, it is good to take off the gradient coil
for that and it is not that straightforward (wiring can be broken and etc.)
Once, I observed the magic that the tuning range rolled back after a while,
so one more iteration in adjusting the frequency was needed.
Much less probable the tuning capacitor is getting stuck so the range is
restricted. In that case, the ATMA may complain with the error
"motor .. can not be set to the position .... or so."
--
Regards,
Dr. Pavel Yushmanov,
+46736220672
P&L Scientific Instrument Services
Applied Physical Chemistry, KTH
Teknikringen 36,
100 44 Stockholm
Sweden
pavel_at_plscientific.se
http://www.plscientific.se
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