Keithley 196 System DMM Teardown

[idpromnut]

Hi, just a quick tear down of the Keithley 196 System DMM 6 1/2 digit multimeter.  Enjoy!

EDIT: I uploaded the operation and service manual here http://www.filedropper.com/keithley196im

[don.r]

Thanks! Now I don't have to tear mine down to see what's inside! And double thanks for the service manual!

PS I don't think that unit has had a lot of hours on for its age. The LM399 doesn't even look remotely scorched.

PPS: Triple props for having a PDP 6050(C?D?) in the background. More LM399 goodness.

[MartinX]

Interesting I want one of those, I have a 195A today unfortunately without AC or current measurement because it is an option not fitted to my 195A.  The 196 looks quite different inside. The capacitors in the power supply looks to modern to be original, have you been doing some preventative maintenance?

[idpromnut]

Heh, np, and I have another 6050A of dubious working condition on its way to my bench as we speak; that'll make for a couple of good repair sessions!

And yes, they are a 605C and 6050D!

And totally chuffed at having a 196 in such a seemingly good condition; the auction said "powers on" only...

[idpromnut]

Interesting I want one of those, I have a 195A today unfortunately without AC or current measurement because it is an option not fitted to my 195A.  The 196 looks quite different inside. The capacitors in the power supply looks to modern to be original, have you been doing some preventative maintenance?

As you see it was as I received it, no changes made by me (other than to pull it apart and photograph it). I was wondering about the caps myself, but I don't know when it was in production.

[Vgkid]

 Thanks for uploading the teardown of the keithley 196 meter. I'm rather suprised at the accuracy of it, despite the lack of trim pots in the unit.

[sync]

Thanks for uploading the teardown of the keithley 196 meter. I'm rather suprised at the accuracy of it, despite the lack of trim pots in the unit.

Software calibration. The hardware doesn't need to be accurate. A percent difference is not a problem. The software will compensate that. Of course the hardware has to be stable.

[idpromnut]

Thanks for uploading the teardown of the keithley 196 meter. I'm rather suprised at the accuracy of it, despite the lack of trim pots in the unit.

Keep in mind that I don't have access to a properly trace-able calibrated source or meter.  I am using a combination of an HP 3478, a EDC millivolt standard and a couple of other meters for sanity's sake and assuming that the chances of them all being off by the same amount as being very small. So the actual accuracy of the meter is still somewhat questionable, if I am not screwing anything up.

[don.r]

These meters can be stable for many years after calibration. A real bargain for 6.5 digits.

[Vgkid]

That would explain the lack of trim pots, didn't realise that it worked on a digital calibration.

[calin]

I have a chance to get one of these 196 for about 150$ ... but is broken ... the meter turns on etc but it does not measure anything .. seems to move around few mV on DC same on AC .. dunno the others.

What you guys think .. somewhat fixable or I should spend my 150$ on beer ?

[sync]

Probably fixable. Maybe a calibration is necessary after repair. BUT 150$ is way to much. You can get working ones for this money.

[idpromnut]

I have a chance to get one of these 196 for about 150$ ... but is broken ... the meter turns on etc but it does not measure anything .. seems to move around few mV on DC same on AC .. dunno the others.

What you guys think .. somewhat fixable or I should spend my 150$ on beer ?

If it's 150$ all in (including shipping) then yeah, perhaps it is worth it.  A friend of mine is also looking at this model of meter that's broken. We did a quick analysis on the design and schematics, and yes, it looks like if the analog front end is borked, it is mostly discreet chips/components that can be found currently. The digital backend is a different story.  I would try and see if any of the program stuff works; if so then the digital backend is probably working.

[coromonadalix]

The Keithley 196 analog board is almost 90-95% identical to the Tektronix DM5120, the 5120 has optocouplers  vs the 196 has isolation transformers

The logic is very different, simpler design in the Tektronix DM5120