This is my little Christmas endeavor, contribution into making my Keithley DMM6500 much more quiet.
I bought the instrument more than two years ago. I really like things to be quiet in my Lab so this new wonderful Keithley came to shame
with its really loud fan. It was also very buggy, blue screens almost all the time. Some Firmware revisions later, 1.03, and it was usable.
Due to the fan it became a dust collector, just using it occasionally for some special measurements and not as my every day companion in the lab.
Some weeks ago when turning the instrument on the dates where reset back to 1970. Digging into this it became clear that Keithley
had made a mistake draining the backup battery to quickly and there was also a new FW that should correct it to some extent.
This battery issue became the start of the modification. To summarize:
• Change of Battery. (Broke the battery holder, had to make a special solution).
• Update to latest Firmware (FW). Not painfree, but almost.
• Ventilation holes in lid.
• Move the original Fan and modify it with a diode in series to slow it down.
◦ It could probably have been run Fan-less, see measurements and links at the end.
Sorry to say but Keithley seems to have cut corners in this design, especially around the power supply, thereby wasting a lot of power into heat.
• They have used two transformers in parallel with low primary inductance's making the standby power more than 6 W.
So yes, have a switch turning the instrument of completely!
• Used linear regulation for the analogue parts with very large voltage margins.
See attched PDF with my report. Not complete in any way but I hope it helps !
)) Per
N.B ! Disclaimer. If you do this you do it at your own risk. I can't be held responsible in any way!
(Should probaly not have to write this here
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