Audible noise from Keithley 2700: normal? - Page 1
Forum section: electronics / testgear

author: jp430bb
author_rank: Contributor
timestamp: January 06, 2018, 03:41:49 pm
content: I've got a Keithley 2700 bought used via eBay. It seems to work fine, as far as I can characterize it, anyway. However, there is a faintly audible noise coming from it. It's a sizzling noise similar to the sound of a small wind-up toy running. I thought it might be inverter whine or a ceramic capacitor's piezoelectric effect, so I turned off the display by sending "DISP:ENAB OFF" via GPIB. The noise did not change, but it's possible that the VFD inverter keeps running, and the display-enable-off command simply disables lighting up any segments.Is this kind of audible noise normal?By the way, I also have the ~10mV spikes in the oscilloscope trace reported inhttps://www.eevblog.com/forum/testgear/bench-meter-noise-injection/msg318068/#msg318068. I guess it's common-mode noise like Dave discussed in #594.

author: mcinque
author_rank: Unknown
timestamp: January 06, 2018, 05:49:48 pm
content: Could be some free wound inductor part of the SMPS not properly glued? Did you try to touch it every single inductor with an insulated stick to see if the sound stops?

author: MadTux
author_rank: Frequent Contributor
timestamp: January 07, 2018, 12:33:30 am
content: As far as I can tell, all Keithley 2000s and friends like 2010, 2015, 2700...... do that. I'm not exactly sure what causes it, but it seems to originate from the VFD. Perhaps vibrations of the VFD filament wire? I'm not sure, but I don't care that much, as long as the instrument works as it should. Want a quiet instrument with only relays clicking, use something old with LED display, like HP3456, Keithley 196 or a Fluke 8505.

author: petemate
author_rank: Regular Contributor
timestamp: January 07, 2018, 07:09:06 am
content: The Keithley instruments I haved used do that as well. But once the relay cards on that 2700 starts clicking you'll forget all about it

author: exe
author_rank: Unknown
timestamp: January 07, 2018, 10:17:52 pm
content: My 2000 is almost silent, just some transformer hum.

author: jp430bb
author_rank: Contributor
timestamp: January 07, 2018, 11:08:57 pm
content: I haven't opened up the meter, so no, I haven't tried touching anything to see if the noise stops.From what the others have commented, the noise is typical, so I won't worry about it.

author: TheSteve
author_rank: Unknown
timestamp: January 07, 2018, 11:42:54 pm
content: I do believe it is common. If you have a picture of the main PCB I can show you the ballpark area it originates from. You can add a really big capacitor and it will stop.

author: jp430bb
author_rank: Contributor
timestamp: January 08, 2018, 01:39:50 am
content: I was worried that the noise was a sign of an incipient failure, but knowing that it's normal, I'll live with it.

author: azer
author_rank: Regular Contributor
timestamp: January 11, 2018, 07:42:59 pm
content: It is coming from the area around regulator close to the connector to the front panel if I remember correctly. I tried poking components to dampen the noise, but never found the culprit. The noise will go away if you disconnect the front panel.