Thanks to the AMMRL community;
We definitely had a bad 5V/50A supply with .7Vpp sawtooth ripple. The
filter caps on it had gone bad, they were hot and they read ~15-20% of
their rated values! ... but our Electronics pro's could not source them
at the right size so we ordered another supply. When it gets in we
shall see if the several problems disappear. They offered me a
switching supply with the same spec's but I declined.
I am hoping that having the bad supply did not damage anything. I will
update with news when we get the new supply. I've got a lot to check
when it does arrive thanks to my generous colleagues counsel.
I have listed all the responses below.
Regards,
Robert Harker
Engineer
University of Florida
Dept. Chemistry NMR Labs
Gainesville, Florida 32611-7200
352-392-4650
352-328-5862 Cell
====================================================================
> You could have three independent problems, but the simplest
> explanation of all three sets of symptoms is that one of the low
> voltage DC power supplies is failing - hence the sidebands/glitches at
> 2 x line frequency. A quick check with an oscilloscope should show up
> any smoothing problems.
=======================================
Is there any chance you have a console wired for 220 V, but you are
running it on 208 V, and the voltage is just a tad low? It only has to
drop a few volts down (say to 203) before it hits the fan. Your symptoms
in part C sound like that to me.
=========================================
I am experiencing 120 Hz noise on a Unity 500 console right now.
Prediction from our electronics guy is that it will turn out to be
power line frequency (rectified so it's 120 Hz) coming in through the
main power supplies due to deterioration of some capacitor which is
supposed to smooth it out. Probably visible as a ripple on the
backplane power supply lines. We haven't had a chance to investigate yet.
I'd be curious if you get any more specific suggestions. I'll be happy
to compare notes.
=================================================
Hi Robert,
We used to have a couple VXRs here many years ago, and the biggest
problem I remember is the SCSI bus. My only advice for that is to be
sure of the correct terminations, minimise the bus lengths, reseat all
cables, and keep the fastest, widest devices nearest the host. Varian
had an old Service Note regarding this.
Otherwise, an instrument of that age will need to have the circuit cards
reseated and a good cleaning out of dust before making conclusions about
intermittent problems. Take precautions against static electrical
buildup and discharge when cleaning out dust and reseating the boards.
It would not hurt to clean the card edge contacts while you're at it.
You'd be surprised what a good cleaning can do to improve operation of
an old console.
As far as the 120 Hz noise goes, you have a bad AC line power supply.
The age of the entire console is such that the filter capacitors are at
the end of their natural lives. It could be the console supply, or more
likely the synthesizer or amplifier. PTS synthesizers are notorious for
bad filter capacitors at that age, so yours definitely need to be
checked. You can test all power supply voltages with a multimeter; AC
ripple should be less than 10mV on all supplies. You have to take a
cover off the PTS to get to its power supply. If the VXR has an ENI
amplifier, then that could also be where the bad power supply is, and
you have to open it up also to check for ripple.
IIRC, the VXR console has several hidden fans. I don't remember
specifically where they are, but if you check every card cage top,
bottom, and sides, you'll likely find some you did not know were there.
Use a flashlight and look VERY thoroughly and replace any that are not
running. The old Varian Gemini console power supplies have a blower
hidden in the center of the power supply drawer, and you must pull the
power supply cover off to find it; I don't recall whether the VXRs have
that or not.
The real puzzler to me is the FID spike at 2.67 seconds. I suggest to
change the number of data points (digital resolution, or dwell time) to
see if the spike moves. I might also try other parameters, like pulse
delay or Acquisition Time to see if the spike moves. You could also
disconnect the audio (FID) signal between the Receiver and ADC to see if
it disappears.
Best wishes,
==================================================
Hi Robert,
Check the digital card cage supplies for
proper DC voltage and AC ripple; I'll bet you
have a bad DC power supply, maybe a bad filter capacitor
on the +5VDC supply.
A bad supply can cause all your described problems.
Cheers,
================================================
Hi Robert,
It sounds like a digital issue to me. I would start with swapping out
the STM board and see if the errors go away.
While monitoring the boot up, the console needs to go to a status-"idle"
in order to work properly.
When opening the acqi window, the acquired lock data is ADC'd and passed
through the STM for digital display in graphics mode.
That is probably why a reboot is occuring. The SCSI is panicing when the
STM traps out.
I do have an entire VXR 200 console and digital rack collecting dust in
my garage.
Let me know if you're interested in any items you may need.
I'll be happy to gather them for you for the price of shipping and a
small labor fee based on the actual time it takes to remove them from
the console.
The parts ( what ever you want) are yours for free.
Best regards,
====================================================
Dear Robert
Glad to be of help. When I had the same problem I diagnosed it by poking
each big capacitor in turn with a finger - nothing, nothing, nothing ...
OUCH. Not recommended!
From memory I didn't even have to take the faulty power supply out,
just replaced the capacitor, which had screw terminals, in situ.
Best wishes
=================================================
Dear Robert,
It has been long for me having worked with VXR, but I recall
this kind of unusual problems have appeared, when digital
card cage 5 Volt power supply developed excessive ripple in
the power supply. This happens because of failure of
capacitors because of heating. Please check the capacitors
and replace them. They are situated on left side bay, down
wards, the blue big and high value capacitors about 78000
microfarads about four to six of them. If problem persists,
do write to me, I have discarded VXR 300 some where to dig
out the board you need.
Regards,
==================================================
On 7 May 2012, at 20:00, Robert Harker wrote:
Dear spinlanders;
We are scheduled to replace this very old VXR300 but in the meantime we
have been troubleshooting the following issues:
A) Intermittent un-commanded system resets.
1. Immediate system reset on opening the shim window in ACQI.
Sometimes it requires manipulating shim buttons.
2. With shim offset board removed from the circuit ... NO RESET
3. Still has un-commanded resets during ACQI SHIM interaction.
4. Only happens when the Shim window is open in VNMR.
B) STM Board errors as recorded by a diagnostic terminal..
1. Multiple STM Board Errors indicating the same addresses
* STM Error; STM reg = 0x8002, count=-1, address fffffea6
* STM Error; STM reg = 0x8002, count=-1, address fffffa602
* STM Error; STM reg = 0x8002, count=0, address fffffa602
* STM Error; STM reg = 0x8002, count=0, address ffffffeaa
* STM Error; STM reg = 0x8002, count=0, address fffffa5fe
C) Acquisition errors when running a standard proton experiment on
dueterated water
1. Major spike in the FID _at_ 2.067 sec
2. Noise in the FID distributed / separated by ~.00839sec =)> ~120 Hz
in the spectra.
So we are looking for advice, the STM card and the SHIM-OFFSET Card for
the VXR300;
Thanks
Robert Harker
Engineer
University of Florida
Dept. Chemistry NMR Labs
Gainesville, Florida 32611-7200
352-392-4650
352-328-5862 Cell
Received on Mon May 14 2012 - 04:55:42 MST