I made a copy of the discussion below from the now-defunct Varian/Agilent
users' Slack group. This may help:
*Protune: Motor clutch problem may kill AutoX probe capacitors*
Bert Heise
2015-08-01T16:35:24.375+0000
Recently I have come across a problem that appears to be a general issue with
the "traditional" Protune units (with 1-4 external stepper motor units). This
one turned out to be a probe killer:
The Protune motors contain one slip clutch each to prevent too much torque
being applied to the capacitors that could break them.
The slip clutches of the company **_Machine Components_** used in most of the
Protune units (in the beginning clutches of a different manufacturer were
used) are using special grease to effect the slipping without rubbing off
material from the clutch.
Unfortunately, this grease can deteriorate and become sticky like honey
instead of lubricating properly. This sticking clutch leads to an increase in
the applied torque which in turn may break tuning/matching capacitors
(especially vulnerable are the high-band capacitors because of their smaller
size) or the G10 axle shaft that drives the capacitors (this typically happens
with X Tune/Match capacitors where the capacitor itself is much bigger and
breaks less easily - with these the thin hollow-drilled section of the drive
shaft is the weakest point that breaks).
In order to find out if your Protune motor module may be affected, do this:
Switch the motor box off, then hold the rotating part on the backside with one
hand (see picture below) and rotate the respective black knob on the front
back and forth.
The rotation should be smooth, without hesitations or stickyness. If the knob
appears to stick - especially when reversing the rotation - the clutch is bad
and needs to be regreased.
(See Figure 1)
If you find you have the older type clutches (see below these are not made by
Machine Components) you may be fine - at least these don't appear to have
grease that may get sticky. I have the impression though as if in this case
the high band motors have the same clutches as the low band ones - which is a
bit firm for the weak high-band capacitors. Someone at Agilent please confirm
this - these units are unmarked unlike the MC ones...
(See Figure 2)
After removing the clutch and opening it you may notice a pungent smell of the
deteriorated grease. It also will look brown in colour.
**NOTE:** Slowly rotate the outer and inner parts against each other while
pulling them apart - you don't want to deform the spring. Don't just pull them
apart as it may deform or even break the embedded spring!
(See Figure 3)
The old grease is best removed with dichloromethane or similar polar solvents
(acetone will work but takes much longer):
(See Figure 4)
Then new grease is applied. I use the original grease obtained from the clutch
manufacturer, but ordinary ball bearing grease will equally do.
(See Figure 5)
I can offer to perform this service for you if you want. I have done this for
a couple of customers already - unfortunately for a few of them it came too
late as one of their probe's capacitors had been broken already. Maybe Agilent
Service should provide this special grease to all current Protune owners...?
I can also repair probes for which this Protune maintenance has come too late
and one of the tuning capacitors (often the high band tune or match ones) are
broken: Typically the tuning shaft rotates without end as the end stop is
gone. Still it is important to do the clutch service because chances are that
the newly repaired probe will break again right away...!
\- Bert
Bert Heise2015-10-18T22:19:09.586+0000
Video of checking a (badly) stuck slip clutch by holding the tuning rod on the
back side while rotating the black front knob. It is hard to rotate it,
especially when reversing the direction:
(See Figure 6)
Video of checking the same coupling after repair (clean + re-grease):
(See Figure 7)
I have done this repair approx. ten times so far (in about six months) and
have found only **_one_** Protune unit so far that did **_not_** have (at
least partially) stuck slip clutches!
Unfortunately, until very recently at least Agilent only "solved" this problem
by sending customers a replacement Protune unit - which can have (and
**_did_** have!) stuck clutches as well... I have heard of customers whose
main probe broke more than once in one year because of this...
I hope Agilent starts to **_really_** do something about this!
Craig Butts2015-10-19T06:51:32.453+0000
Thanks Bert - that is fantastically useful!
We have stopped using Protune on one system entirely (and probably a second
now) due to continual breaks (once every 4-6 months, retuning 50+ times per
day).
We'll pull our systems apart and do this ASAP (and regularly afterwards!).
Bert Heise
2015-10-19T08:29:28.336+0000
Hi Craig,
as my blog entry has very few views (there should be a lot more Protune users
out there...) I probably have to start a discussion thread about it to make it
more visible...
You should be fine for at least 1-2 years I guess, and re-checking is totally
easy - just switch the motors off, hold the rear axles and turn the knobs one
by one. The resistance should be smooth and not sticky.
Cheers
Bert
Craig Butts2015-10-19T09:07:11.665+0000
Oh they are sticky all right. In fact "lumpy" describes the feel better....
Bert Heise
2015-10-19T18:01:28.672+0000
You'll also notice the typical stink of degraded grease when opening the stuck
couplings...
**
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Received on Mon Mar 10 2025 - 14:50:10 MST