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Random Buzzing Noise on E36313A Even When Powered Off

Question asked by glowitz on Nov 20, 2017
Latest reply on Jan 10, 2018 by glowitz

I have a new E36313A Triple Power Supply and have an unusual symptom. I am working with customer support, but so far have not been able to resolve the cause. In parallel, I'm reaching out to the Keysight community to see whether anyone has experienced a similar symptom.

 

Description of Problem

 

When plugged in to a power strip (which also has its own surge protection built-in), and with the unit powered off, I hear a periodic (but random) buzz that sounds like something oscillating or vibrating inside the unit (even when turned off). The noise is definitely coming from the unit itself. 

 

I also tested it under a few watt load and the problem exists regardless of whether it's on or off. When the unit is turned off, it still draws about 130 mA, so the power supply must be in some kind of standby mode awaiting it to be turned on via the front panel. Sadly, this seems like a waste of power (about 13 Watts in standby/off mode).

 

So, I happen to have a data logging plug load monitor. Attached is one chart where you can see that the current suddenly spiked from about 134 mA to nearly 1A for a second or two. Generally the buzz lasts just a second or two, so this spike seems to correlate to this intermittent symptom.

To rule out the power strip as a possible source of the problem, I moved the unit to a different part of the building and a different circuit. While it's plugged into a power strip, there is no surge protection on this. I don't believe this issue has anything to do with the power strip.

 

I re-ran the tests twice overnight. One without load, one with load. In both cases, I see periodic small current perturbations, followed by a few "large ones" where the current spikes nearly an amp for just a brief amount of time. To help rule out that it's a power spike, I also measured voltage and don't see any spikes at the time the current spikes. One point, the logging interval is 1 second, which may miss some very fast spikes -- but generally when I hear it buzzing, it lasts for 1-2 seconds or a bit beyond.

 

I'm trying to determine whether there is something wrong with my unit, or whether there is a design situation that's sensitive to some environmental condition, or whether this is expected behavior (for example, does the instrument do something even when powered off that would cause a sudden but short surge in current)? And related to this, why is the instrument wasting 13W while turned off -- what's the purpose in keeping a low level of current flowing to the instrument unless it's to help stabilize some of the circuitry so it's always "ready" to go...

I would appreciate anyone from the factory or customer with this unit to chime in with any ideas.

Thank you!

 

Greg.

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