Thank you Spin-Doc and Shawn-Wagner and everyone else who responded to my query.
It turns out that the TTL is in fact being held at 5V. During an "su" it
drops to 0V momentarily but the regardless of the channel selected for observer,
it returns to 5V. It seems quite strange to me that a ttl line would fault
toward its 5V state. I have tried various swaps with the master controller
and master interconnect but have seen no change in this behavior. Does
anyone know which PS lines to check that could influence the TTL behavior? I
can easily put them on my scope and see the noise on each line but don't know
what is good and bad.
Regards,
Scott
Scott K. Smith, Director of NMR Spectroscopy
The University of Texas at Austin | Chemistry | 832-294-1928 | utexas.edu
> From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> On Behalf Of Spin-Doc
> Sent: Wednesday, March 27, 2024 5:41 PM
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] MR400 LO switching
Hi Scott,
are both 400MRs using a synthesizer board (to the right of the leftmost Ref Gen
board) or are they using a 19" VFS synthesizer module?
The synthesizer boards are known to be a source of problems. May be worthwhile
testing the other channel by swapping the RJ45 as well as BNC plugs between Ch1/2.
Did you check all voltages on the Molex plugs in the bottom right side of the
console? Any browning on any of the power supply pins?
Best regards
Bert
> Am 27.03.2024 um 18:40 schrieb Smith, Scott K <scott.smith_at_austin.utexas.edu
I am sure nearly everyone has had to track down a missing signal.
In this case the root cause in somewhere in the MR400's LO switching device.
The MR has a single receiver box for both channels. The LO used in detection
is pre-selected by an external module (Mini Circuits RF switch ZASWA-2-50DRA+).
In short, this switch is no longer passing through high band LO to the receiver
making it appear that there is no signal. It looks like the LO for low band
channel is passively allowed through, so one gets the curious result that a carbon
spectrum with full proton decoupling can be acquired while nothing not even tuning
works on the high band channel. All the transmitter pathways checkout as do the
LO's themselves. Proton work if I manually swap the LO input cable directly to
the receiver.
Are these mini circuit devices known to just quit working? Or might there
be a problem with the power-supply and TTL control lines feeding the switch?
I now have two MR's with this error.
I would appreciate any suggestions or help I can get at this point.
Cheers,
Scott
Scott K. Smith, Director of NMR Spectroscopy
The University of Texas at Austin | Chemistry | 832-294-1928 | utexas.edu
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Received on Thu Mar 28 2024 - 18:26:08 MST