Advice for Tek 4051 vector-drawing issue?

Josh Dersch wrote: My Fluke 25 won't go that high either -- max range on that is 32 megohms. I've got a Solartron 7150plus bench DMM that can read down to one milliohm in the 2K-ohm range (6.5 digits with averaging enabled), but still limits at 20M-ohms max. The spec in the parts list was 1%. 1% of 39M is 390k-ohms either way... 40M is well out of spec. I'd have used a 20M, a 10M, an 2.2M and a 6.8M in series which gets you 39M exactly, and if you use 1% resistors you should be within 1% of the final value (assuming my math is accurate, which it probably isn't). Note that all of those are E12 values, i.e. standard resistor values. Well, based on what you've done, that leaves the capacitors and the opamps (as you've already said). There is a note on page 5-26 of volume 1 relating to the test fixture and the vector display -- specifically: Don't worry if both directions of vector drawing do not close for the deflection magnitude may be well out of the linear range of display deflection parameters. I've just been (re-)reading Jed Margolin's "Secret Life of Vector Generators" article (<http://jmargolin.com/vgens/vgens.htm>). There's a bit in this article about capacitors in analog vector generators... and how picky the integrators in AVGs tend to be..... I'm starting to wonder if some normally-irrelevant parameter of those poly caps has shifted and fragged the vector generator. Catch is, because both channels are intended to be matched (there's a bit about that in the theory of operation for the vector generator in Vol 1, IIRC) you might have to replace the same parts in both channels to get everything to match up... No problem. -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/