Keithley DMM6500 - Teardown, Demonstration and Mains Transformer Replacement

This is a quickly produced video on replacing the mains transformer in my Keithley DMM6500 due to the known "Hum" issue that plagued some early units.
Please excuse the handheld videography and quick editing as this video was shot on an iPhone whilst undertaking the repair.
See my other videos on this channel relating to my Rohde and Schwarz RTB2004 oscilloscope, Keysight MSOX3014T and various other Lab. equipment.

[@violentsense]

Thank you for sharing! I have the same problem and two weeks ago I contacted the seller, because my DMM6500 is still under warranty.

[@michaelrothschild2646]

Since I changed the transformer the DMM6500 is a pleasure to have powered-on in my Lab. I previously found the hum noise would vary from day to day and although not terrible it could become annoying. I hope you have it repaired swiftly. I found Keithley’s customer service excellent; all my queries were responded to very quickly and the replacement transformer was supplied very promptly (especially given the Covid situation). Kind regards Michael.

[@comprotudo]

Just check mine, 02/21 and he as the new transformer. Tks for the nice video.

[@supercompooper]

I inherited a big box of milspec Vishay 0.001% resistors. I'm dying to characterize them on a Keithley Sourcemeter :)

[@CASKP]

Hello, I also own a DMM6500 and have the same problem with the transformer. Unfortunately this is the case with these meters. I did not know that it is possible to get a new transformer. I have to write to Keithley again.

[@andpe161]

I have an early(?) unit. It had the hum, I sent it back for repairs. Afterwards it has a very faint hum that I don't notice in my daily work.

[@michaelrothschild2646]

Hi. I think the faint hum you can hear is because the transformer is mounted metal to metal. I was considering making and fitting a rubber gasket (small rectangular piece of rubber 21.00) between the transformer mounting plate and the body of the case to which it is affixed. Currently, my DMM6500 is very quiet and really I only hear the slightest noise from the fan. I am now delighted with my 6500 and I am practising using Lua coding with it; this makes it extremely adaptable and powerful from a workflow point of view. Stay safe. Regards Michael

[@JonatanSmith-e3w]

I would like to know if after changing the transformer. I continue with the noise or you continue to hear very little or '0' noises. Since I have acquired one and it makes noise, I only put it to the network while it is in standby (not turned on). I'm up to the manufacturer's response. Thank you.

[@innocoach9476]

I just got a new unit, manufacturing date 12/2020, and guess what: there is a loud hum when the unit is plugged in and in stand-by mode. When I press down on the case, the hum is reduced some. It‘s difficult to compare sound levels when listening to a video, but the loudness of the hum of your unrepaired unit seems to be on par with my new one. It‘s rather disturbing when it‘s quiet in the lab...

[@michaelrothschild2646]

Hi. Really surprised that your unit would still have this issue. How do you know the manufacture date? I can only see on my unit a calibration date which was 15/05/2018 and I bought my one from Farnell in the UK in mid June 2018. I would suggest that you have a word with Keithley’s Customer Services whom I found really helpful. Just one final comment, I assume your noise is coming from the transformer and not the cooling fan, to confirm this my unit was noisy if plugged in but not actually powered on (soft-start mode with only orange power led showing). I don’t think the fan they use in the unit is that silent running either! Hope you sort the issue. Regards Michael

[@innocoach9476]

@@michaelrothschild2646 Before I forget: thanks a lot for your video, otherwise, I wouldn‘t have known that this is a known issue!! Hum: The noise clearly comes from the transformer, if the unit is plugged in but not switched on. The fan noise is okay for me: when the DMM runs, normally, everything else in the lab is switched on, too (so, there‘s ample noise). On the other hand, there is such a clear trend towards „anti-noise pollution“ everywhere, it‘s difficult to understand that manufacturers don‘t consider this more. How much does a rubber isolation cost? The manufacturing date is indicated on the box the DMM came in: „Date of Manufacture: 2020-12-17“. Clearly a newly produced unit. I talked with the main Tek importer for Switzerland this afternoon, and he confirmed me that the issue is known for the older production runs, but not for recent units. I have purchased my unit through another reseller where I have the option to send any purchases back within 14 days. An option I‘m going to take. The Swiss main importer offered to send me a new unit next week with a kind of „test before you buy“ deal. Nice! Thanks again for your work and best wishes - Chris

[@innocoach9476]

Hi Michael, I wanted to keep you updated: I just got another DMM6500 (manufacturing date: Nov/2020) from Switzerland‘s offical main importer, and it has the same transformer hum. I checked the eevblog, and there are recent (Q4/2020, Q1/2021) entries from customers who bought new units with transformer hum. They were able to send them back for repair and got units back without any hum. Just like your device after the transformer replacement. My hypothesis: Keithley produces the humming units, because they are cheaper than the units with the better transformer. And for most customers (e.g., in a production environment), this is okay - they don‘t even notice the noise. If a customer complains, they replace the transformer. I can well imagine that this procedure saves cost. I have a „try before you buy“ deal with the importer. I‘m going to talk with them (they are really nice) and ask them, if they are willing to have my unit repaired before I buy it... strange world... Happy Easter - Chris

[@bendemir3004]

Keithley Europe will simply ignore you about the problem. The hum of the DMM6500 transformer will get worse over time. It makes me really sick and I never use this multimeter just because of this annoying noise. I prefer my trusty Keysight bench DMM :)

[@enesozver9606]

hello, where can I get this transformer from? can you give me a link?

[@miltoneduardososa378]

Is keythley already aware about that issue?

[@michaelrothschild2646]

Absolutely. This problem only affected some of the very early units and I believe it was rectified on later units. Keithley would have repaired the unit free of charge(replaced transformer); however I didn’t want to send the unit by courier because of it’s handling in transit from a possible damage/calibration issue. Keithley customer service was excellent and I am now delighted with the unit. I am going to be making some further videos shortly on programming with TSP and the internal trigger/data logging capabilities which are really fantastic.

[@miltoneduardososa378]

@@michaelrothschild2646 I will wait anxiously for that video then. I think after it, I will finally make the decision of going for this device or not. Rich logging capabilities is one of the things I am looking forward to see in a device like this one. Do you think it will make the job to log V and I (form uA to mA) for IoT devices? Or should I go for a Qoitech Otii?

[@michaelrothschild2646]

@@miltoneduardososa378 Dear Milton I will over the next few weeks post another video on data-logging. The Keithley really is very powerful for data-logging and I luckily managed to buy from eBay a 20 channel 2000 series data-logging card cheap a while back (around £60.00). I think the DMM6500 is very powerful once you learn TSP scripting based on Lua; you can also create very detailed trigger setting (used for logging) within the meter as flowcharts (still learning this). I also have an Otti Arc device which is great for power calculation data-logging. The software for the Otti works really well on both Mac and Windows. You should however note that with the Otti Arc you are limited to data-logging generally at a maximum of 5volts; although you can use an external shunt resistor and enter the value in the software. The Otti Arc also doesn’t sample as fast as the DMM6500, it either samples at 4ksps (up to 19mA) and 1ksps (in higher current range up to 5Amps). The Otti also requires quite expensive separate paid licenses for the Battery Toolbox, Otti Automation Toolbox and the Otti Log Toolbox. I personally consider the Otti really suitable for lower power (and voltage) power consumption data-logging. The Keithley is more suitable for higher voltage data-logging as you can obviously use with either DC and AC voltages which are much higher. I have seen TSP scripts written specifically for power calculation logging as the DMM6500 has a ratio function which can be used to measure two voltages simultaneously using the sense ports which is a really clever workaround. Hope the above helps with your choice. Stay safe. Kind regards Michael

[@Mr1Spring]

get a tripod please

[@michaelrothschild2646]

Hi, I did mention twice in the video that unlike my other videos shot with a proper full-frame (35mm) camera on a tripod, this one was a very quick video shot on my iPhone whilst I undertook the repair. I shot it in this method as I assumed this video was a speciality one for people with a Keithley DMM6500 and the transformer hum issue that plagued the very early units. Hope this clarifies why I didn’t use a tripod and spend hours filming and editing it.