Teardown, Repair & Calibration of a Valhalla 2701C Programmable Precision Source - Page 1
Forum section: electronics / testgear

author: Hugoneus
author_rank: Frequent Contributor
timestamp: January 12, 2016, 06:13:53 am
content: You can watch the video here: [26 Minutes]youtu.be/e-UwxRhYLS8More videos at The Signal Pathhttp://www.TheSignalPath.com

author: HighVoltage
author_rank: Super Contributor
timestamp: January 12, 2016, 11:38:46 am
content: Thank you for another great video.Although, it is almost vintage, it seems this one is still available brand new today?0.5 ppm resolution.http://valhallascientific.com/instruments/calibrators/model-2701c/

author: Dr. Frank
author_rank: Super Contributor
timestamp: January 12, 2016, 01:47:49 pm
content: The brief look inside was quite interesting, and promising.Anyhow, I missed further teardown details, schematics, specifications, as you usually do in your other great RF videos.It would have been much better to settle the Keithley 7510 on top of the Valhalla calibrator, so both instruments were visible, and the audience could actually follow calibrator settings versus DMM readings.It was a pity, that the calibration process was not transparent.The calibrator needs 10 sec to settle to each new setting, so mostly each measurement was too fast.Also, before this cal process, a brief look into the 7510 specifications and date of last cal would have been very useful, to determine, if the 7510 really is capable of doing that calibration properly, in terms of uncertainty and stability.For 100V and 1kV range, probably this mysterious Keithley version of the "autocal" feature would have been necessary to apply before calibrating these ranges.I'd like to see a follow up under this aspect, maybe also adding the current source capability.Frank

author: Hugoneus
author_rank: Frequent Contributor
timestamp: January 12, 2016, 03:57:35 pm
content: Dr. Frank,I will make a followup video and will address some of the questions you have raised. This was supposed to be a quick overview once I realized the unit didn't need a major repair. I also would like to measure all the caps to make sure they work.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: January 12, 2016, 07:39:41 pm
content: Also, I am not 100% sure if upgrading the reference would give much better performance, but I would like to see the potential for getting the current option.Does anyone have the firmware for it?

author: eas
author_rank: Frequent Contributor
timestamp: January 12, 2016, 09:08:53 pm
content: I think the 2701C is basically an update on the basic design of the 2701B. At a high level, its clear that they've refined the PCB layout, and the MCU replaces 7400-series based control logic.One thing I found interesting about the 2701B is that there is a pre-regulator stage before the regulated output transistors in order to minimize the power dissipation. The pre-regulator is a simple switching supply. It switches the primary supply to the transformer is so that the rectified, filtered output is ~100v above the target voltage of chosen output voltage of the unit.

author: Vgkid
author_rank: Super Contributor
timestamp: January 13, 2016, 03:53:37 am
content: Thanks for the video, I look forward to part 2.

author: quarks
author_rank: Frequent Contributor
timestamp: January 13, 2016, 01:43:35 pm
content: This was my first calibrator and I still like and use it.Thanks for the video and please share more.byequarks