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Electronics => Repair => Topic started by: drhex on January 19, 2025, 03:55:30 pm

Title: SMU200A (B) Synthesis Reference PLL unlocked
Post by: drhex on January 19, 2025, 03:55:30 pm
Hi all,
I have a dual channel 3GHz SMU200A on my desk which shows "(B) Synthesis Reference PLL unlocked". Scoping A and B together they seem to be perfectly stable, I can move the phase in the reference dialog. Ref is on the loop between the SSYNs, removing the loop decouples A and B. Ref is also present on the back connector. Injecting an external reference doesn't make a difference. Service manual suggests changing A2240, I tried two other ones, same error. Internal adjustments pass fine.
All of this makes me think that I either don’t understand what is going on or I have an issue with the reference lock state being communicated correctly to the software.
R&S is its usual stony self, no help from them as no company. I posted in the groups.io R&S group as well.
Thanks,
Florian
Title: Re: SMU200A (B) Synthesis Reference PLL unlocked
Post by: drhex on January 19, 2025, 06:07:07 pm
So decided to completely uninstall the software with the uninstaller and the cleaning script. I then put on SP3 for good measure (yes, not officially supported but I don't have the original install media) and reinstalled the R&S software (latest, 3.20.286.21). That fixed it, at least for the moment.
Now for installing the 6GHz option, does anybody have a set of cables perchance?
Title: Re: SMU200A (B) Synthesis Reference PLL unlocked
Post by: drhex on January 19, 2025, 11:20:02 pm
This didn‘t last long, level adjustment brought the error back. Any ideas welcome.
Title: Re: SMU200A (B) Synthesis Reference PLL unlocked
Post by: DaJMasta on January 20, 2025, 01:02:25 am
Can you see any glitches in the back connector output when the error shows?  It could help determine if it's a problem with the reference oscillator and its loop or if it's the way a synthesizer is locking to it.  Since any external input is still going to be locked into the reference PLL, you can get similar behavior even when using the internal one if it's the loop that has the issue.