New Keithley DMM6500 and now DAQ6510

[maxspb69]

This simple part prevents the PCB deformation  when the front/rear input switch button used.

[voltsandjolts]

Is this part fixed to the metal case, with double sided tape or such like?

[maxspb69]

No, this part simply fits over the PCB edge and prevents it from bending upward when the button is pressed. The upper part  rests on the cover of the device housing.
No additional fastening is required.

[bateau020]

Maybe it is the print house I used, but with 0.1mm resolution in PLA Pro, it fits really tight. So tight that the friction between the PCB and the sidewall is enough to stop the pcb from flexing. And it is really snug to the top. As I'm using the rear/front switch a lot (along with my custom scanner card and breakout box) this is perfect for me.

[0x2102]

So it's now February 2023. If I were to buy a new DMM6500, would it still have these problems?

• Transformer hum (240V, 50Hz)
• Poor viewing angle on the LCD screen

Got my DMM 6500 last week. So, as of May 2024 I can confirm that the Keithley DMM 6500 is still a "bumblebee" and is humming away in standby - sipping 5.2W doing nothing.
The fan is still annoying but distracts from the transformer hum.

The viewing angle is fine for my use but I would say it is the same old display.

Still a bit confused as some folks here say it is silent. I have a tinnitus but I can hear it from 6 meters away - across the room.

I will return it. Not sure if it makes sense to order a second unit to test.

[thm_w]

Still a bit confused as some folks here say it is silent. I have a tinnitus but I can hear it from 6 meters away - across the room.

Units vary, some are near silent. I've left mine on standby <1m away and not noticed it was on.
Since there are no stats with dB values to compare to, I don't think anyone can say what your chance of getting a "good" unit will be. But it does sound worse than average?

[bateau020]

Still a bit confused as some folks here say it is silent. I have a tinnitus but I can hear it from 6 meters away - across the room.

Tried to see if it was the case vibrating? Some of my PSUs have that. It may go away if you put something on top of it or put some stress on the frame or put a small spacer between the transformer and the case.

[Hydron]

Check the mains voltage setting - if it's set at 110 or 220 then try the next step up (120 or 240 depending on region). Might help the hum if you're running highish mains voltage for your area.

My unit was also unacceptably loud when it arrived (much worse than the demo unit I had to compare it to) but was very acceptable after Tek organised to service it and change the transformer (took a while though, mostly due to customs delays, thanks Brexit!)

[skander36]

....

I will return it. Not sure if it makes sense to order a second unit to test.

Not the best choice.
You won't find a better 6,5 digit DMM from performance, features and price perspective.
Better send the DMM for transformer  replacement or put yourself rubber spacers.

[HighVoltage]

My DMM6500 is almost silent, no hum and very little noise from the fan.
I would just return it under warranty to get one that makes less noise.


 

[0x2102]

The case does not really vibrate. I tried putting a small piece of rubber between the transformer and the chassis and that seemed to help a little bit, but not enough that I will ever forget to unplug it from mains.
For a very brief moment I was thinking of dipping the whole transformer into epoxy resin (like I have sometimes seen it with toroidal transformer). 

 I really like the DMM 6500, so I decided to order another unit and see if that one is any better.

[0x2102]

Check the mains voltage setting - if it's set at 110 or 220 then try the next step up (120 or 240 depending on region). Might help the hum if you're running highish mains voltage for your area.

 

Wow, changing the voltage setting from 220V (default) to 240V made a big difference for me. I can still hear a slight hum when I put my ear right next to it, but it's almost silent when I am about 50cm - 1m away from it.
Thanks Hydron!

PS: I struggled it bit finding the information on how to change line voltage setting. FYI it is on page 11-3 in the "DMM6500 61⁄2-Digit Multimeter with Scanning Reference Manual"

PS PS: I claimed victory too early. It was almost silent with the lid off. With the lid back on it better but still audible.

[skander36]

Wow, changing the voltage setting from 220V (default) to 240V made a big difference for me. I can still hear a slight hum when I put my ear right next to it, but it's almost silent when I am about 50cm - 1m away from it.
Thanks Hydron!

Checking for voltage switch can be a good habit for instruments powered by linear sources. Many countries that decades ago was on 220 V now are on 230-240 V (at my home is around 235V but sometime reach 239V).

[Hydron]

Great to hear that helped, even if it's not totally fixed

Out of interest, how high is your mains voltage typically?
Mine runs close to 250V which is asking for issues like this even at the 240 setting, but having had a quiet demo unit meant I knew it could be improved by a replacement transformer.

[0x2102]

Out of interest, how high is your mains voltage typically?

I just measured 239.41V - so perfect match for the 240V setting.

[0x2102]

Received a second DMM 6500 (Calibration Date 4/2024). Transformer hum is even worse than my first unit (Calibration Date 5/2023). 
Really Keithley?

Seems to be a new transformer. No branding or "Made in ..." on it.

I thought/assumed they are doing quality control somewhere in the production process. I am afraid if I send it to Keithley Germany for repair they will return it as is (within specs) and I miss my 14 day return period.
Will try calling them tomorrow but I doubt they will do anything about it.

[Pinörkel]

Upon exploring ways to silence the loud fan in my DMM6500, I opened the device and discovered that one of the four small screws holding the case had a damaged head. I probably did not notice that before, because it was hidden by the rear rubber bumper. Since I have no experience with non-metric screws and the associated terminology, I am kind of stuck determining the precise type of the screws to find a replacement. In addition to that, the screws have a strange countersunk head that I have never seen before. So far, a caliper and the internet have made me believe that it could be something like #4-40 x 1/4 UNC undercut countersunk phillips machine screw. Can anyone here verify that?

I also need the thread type of the bigger screws holding the fan, the front panel and the rectifier. However, the manual mentions that the screw holes for mounting the DMM6500 to a rack require #6-32 UNC screws and the screws in question seem to fit those holes.

I have attached an image of both screw types.

[KungFuJosh]

If you're trying to quiet the fan, it might be more effective to find the appropriate version of these for your fan: https://www.amazon.com/dp/B08XQVJ244/

[Pinörkel]

If you're trying to quiet the fan, it might be more effective to find the appropriate version of these for your fan: https://www.amazon.com/dp/B08XQVJ244/

At least on my fan, noise is not caused by fan vibrations, so decoupling bumpers will not help. If I remove the case, and consequently, the integrated honeycomb shaped fan grill, the fan is quite silent. Nearly all of the noise is created by the air being sucked through the honeycomb-shaped grill holes. At the grill holes, the air is quite turbulent because the fan blades are only a millimeter away and there is a large pressure gradient, which both causes the noise. My hope was that I could design kind of a spacer, that could force the turbulent airflow into a more laminar flow, resulting in less noise. Or maybe smoothing out the pressure gradient with an inserted air filter could help. According to my initial tests, a simple spacer which only increases the distance from the fan to the fan grill will not decrease the noise noticeably due to the large pressure gradient at the grill.

[0x2102]

As you said, the fan is actually not that loud. The voltage at the fan terminal is 2.9 VDC. I added a diode in series to drop the voltage to approx. 2.3 VDC.
This is a good compromise for me. I also tried adding a 3d printed spacer, which made the fan even quieter but the transformer hum became too dominant again.

I finally removed the spacer and just kept the org. fan with the diode mod.

[Pinörkel]

As you said, the fan is actually not that loud. The voltage at the fan terminal is 2.9 VDC. I added a diode in series to drop the voltage to approx. 2.3 VDC.
This is a good compromise for me. I also tried adding a 3d printed spacer, which made the fan even quieter but the transformer hum became too dominant again.

I finally removed the spacer and just kept the org. fan with the diode mod.

Thank you for the reply. I read through some DMM6500-noise-fighting-PDF posted earlier in this thread and tried to find out if there is a solution without reducing the airflow. A very effective way would most likely be to remove the honeycomb-grill and replace it with the classical circular round wire type grill. However, I do not want to damage the casing. So that solution is out of question. Another thing I noticed while experimenting is that the fan is far quieter pushing air through that grill, than sucking the air through. Sadly that does not lead to anything, since reversing fan will mess up the airflow inside the device.