[Solved] Valhalla 2701B Voltage Standard - range selector problem

[jake900]

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. 
But the 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 output
1200v        0100.000              100v
120v          010.0000              10v
12v            01.00000              1v
1.2v           0.100000              10v  (!)  100x too high - & the same as 120v range


Here 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.pdf


I 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 Range


120v Range


12v Range


1.2v Range


Overview 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.

[jake900]

Solved!! it was dead simple really. I should have spent another 2 mins looking at it instead of 30 mins writing this post

2 of the wires in the lower ribbon were snapped.

[lowimpedance]

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 the
Metrology section , but it is quite a different beast inside.

[jake900]

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