[Solved] Valhalla 2701B Voltage Standard - range selector problem - Page 1
Forum section: electronics / repair

author: jake900
author_rank: Newbie
timestamp: January 13, 2018, 03:02:53 pm
content: Hi everyone, I am looking for some help with a repair.I have purchased a DC voltage standard. It is 6 &1/2 digit and should have 4 ranges (1200v, 120v, 12v, 1.2v)The decimal point moves left each time a lower range is selected - as it should.Butthe voltage output on the lowest 1.2v range is the same as the 120v range.For example if i am on the 1200v range and dial in 0100.000 the output is correct @ 100v. See chart below.Range Display reads Actual output1200v 0100.000 100v120v 010.0000 10v12v 01.00000 1v1.2v 0.100000 10v (!) 100x too high - & the same as 120v rangeHere is a link to the only other thread I could find about this piece of equipment:https://www.eevblog.com/forum/testgear/valhalla-2701b/and here is some rather limited information, featuring 3 half pages of schematics at the end of the pdf:http://exodus.poly.edu/~kurt/manuals/manuals/Other/VALHALLA%202701B%20Operations.pdfI have worked in various places which deal with calibration and repair (of things like 17th edition testers) for more than 10 years, but actually I have not been interested in circuit theory and fault finding until more recently. I am looking for some help on where to start with this fault - which I imagine will start with people asking me for more information/photos.So far I have poked around the transistors and resistors near the range selector switch - which seem fine, I have tested that the range selector switch works (which I already knew as the decimal place moves correctly for each range), and I have measured the voltages around the range selector - which are suspicious but I will detail this in a second post.1200v Range120v Range12v Range1.2v RangeOverview of the main board. Close-up of ICs in white box to follow.Area around the range selector switch on the front panel.Back of the range selector taken from the underside of the main board.These are a couple of chips which seem to be associated with the range selection. These are the chips in the white box on the 5th "overview" picture. These chips are CD400IBE Quad Nor, and CD4013B Dual D-Type Flip-Flop.Thanks for reading.

author: jake900
author_rank: Newbie
timestamp: January 13, 2018, 03:23:02 pm
content: Solved!! it was dead simple really. I should have spent another 2 mins looking at it instead of 30 mins writing this post2 of the wires in the lower ribbon were snapped.

author: lowimpedance
author_rank: Super Contributor
timestamp: January 14, 2018, 02:12:18 am
content: Well it's just as well you decided to write this post as we got all the nice pic.Nice easy repair.FYI I did post the schematics for the 2701c model in theMetrology section , but it is quite a different beast inside.

author: jake900
author_rank: Newbie
timestamp: January 15, 2018, 04:19:39 pm
content: thanks! yeah i have searched around and kept seeing information on the "C" model instead.This unit seems to be all good now, the pictures were taken before warm up and casing removed, it's very close to reading the same as any of the other kit I have. I just don't have anything sufficiently more accurate to calibrate it