EEVblog #406 - Keithley 480 Picoammeter Teardown & Calibration

Teardown and calibration checking of a Keithley 480 Picoammeter Dave got from ebay.
This was supposed to be a repair and troubleshooting as well, but Murphy had other ideas.

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[mrkvk]

Dave, it's easy... You've just cleaned the main switch conectors from oxidation by switching it on and off few times.

[billysgeo]

I think the right angle mains cable "strap" on the bottom is there to help the cable wound around the legs (they double as "wound posts" probably).

[LouieMcConnell]

only EEs are bummed when a product works.

[CyrusBrinkworthRAS]

as old it is it is really accurate... they knew what there doing back in 70's, simple & crisp!

[arcadeuk]

It amazes me how accurate alot of your old kit is from this video and some of your others

[GBJN]

Memories :) Used these on a daily basis when I worked for IPL (Photodiode manufacturer), great instrument, indispensable :)

[sbreheny]

Dave: in your explanation of the offset voltage getting multiplied as the feedback resistor goes up - I don't understand why that should produce an increasing error, since the scale factor of the output of the op-amp (i.e., volts per amp) is also going up. I suspect that the reason for the increasing error has something to do with the way they implemented the FET-input buffer on the op-amp but I have not checked the schematic to develop that theory further.

[pbaemedan]

Thanks for a great video. We have 3 of these meters at our facility. They are used in our Electrostatics lab. You referenced the sheilding contact to the lid. The lid is a carbon load polymer about 1 to 5 Gohms. The shield contact provides a discharge path for the surface charge built-up on the plastic lid. Again, thanks for the effort you put into your productions.

[dregenius]

When I was a student at Penn State University the EE stockroom had piles and piles of what appeared to be an early 80's version of that meter. I asked if they didn't replace them with something newer because of budget cuts, and they said it was actually because they'd yet to find a replacement worth their time. I guess these old "Yank-made" Keithley instruments really are worthy of bringing tears to our eyes.. you know, when we actually made good stuff! :|

[CH_Pechiar]

Dave, the right angled power cable coming out from the bottom of the unit is because the cable can be stored by winding it into the groves molded on the unit's feet.

[foxyrollouts]

I love to watch uncle dave fix stuff b4 my nap time

[ViperFallenAngel]

That cord is at the bottom because it was meant to be wrapped around the slotted raised feet :3

[PowllMorgan]

I think Dave is the only person I see on YT who gets upset when things suddenly decide to work after having been seemingly broken ^^

[sammy]

The A/D chips are in the 177 Microvolt too. That same A/D converter showed up again after 2 years in #777 in another precision Keithley instrument. Tripped me out for a sec

[AspectOfTheStorm]

24:06 "I'd be a fool to even touch this thing"

Huh, the video still has 25 minutes. I feel some touching will be going on

[illustriouschin]

i really like the aesthetics of this device

[EEVblog]

That Murphy ensures were metric instead of imperial that are needed to tighten the knob grub screw...

[EEVblog]

I've had confirmation that the mains switch in these vintage Keithley instruments is notorious for this problem.

[maeanderdev]

I've had the same idea. I think it's really the most plausible reason which I can hardly believe.

[andymouse]

I would love it if you did a deep dive into low current measurement.