HP 8116A calibration question

[rcowboy78]

Hi All,

Got a question on an HP 8116A for those that might be familiar with it.

Been trying to do a calibration on one, and let me tell you, its not the most fun thing I've ever had to do. I've actually had to put it a side for now as it takes a lot of time.

Anyways, while working on the transition time section, I can't seem to get it to make the spec that the service manual claims that it can do.

On the overshoot / ringing parameter, I've tried to add capacitance to decrease the overshoot. The only option that is given for this adjustment is to apply 1 pF or install a jumper. Didn't want to install the jumper as this increases ringing, and my overshoot was already high.

As far as the transition time is concerned, I ended up going to a 10 pF cap, which was taking it back to the settings that it came with from the factory.

After trying this for awhile, the best I could get it was with an overshoot at 4.5% and a transition time of about 7.4 ns. While the specs state that the overshoot should be less than 4% with a transition of less than 6.6 ns. All though this isn't terribly far off, it falls out of specs.

Was wondering if anyone had any success with calibrating one of these, and what they did for this particular section.

I don't want to abuse the boards too much as they have some age by swapping components in and out.

 Thanks for all the help.

[dacman]

Be sure to terminate it into 50 Ohm and be sure the filters are ok.

I used to calibrate them and the calibrated units were not limited.  (Rise time and ringing are common checks.)

[rcowboy78]

What exactly do you mean by filters? Attenuator?

[dacman]

I generically call (usually) aluminum electrolytic capacitors filters, even though I've seen them used for other functions.

[rcowboy78]

Gotcha!

There's not a whole lot of them in there for function except for in the power supply. Power supply was pretty much dead on, although I did tweak them just to put it on specific numbers given. There is a few on the left hand side looking from the front, but other then that don't see many on A2, or A3 boards.

[MarkL]

...
Was wondering if anyone had any success with calibrating one of these, and what they did for this particular section.
...

I've gotten through the calibration on the 8116A and it took me the better part of a day with the interaction between so many adjustments.  Plus most of the pots have WAY too much range, making them far too sensitive to set them easily to the optimum position.  The hardest part was the harmonics adjustments at the end.

I did the calibration several years ago and checked it again just now.  My 8116A has about 4.5ns to 6.2ns transition time with <2% overshoot in all the specified conditions.  So it is possible.

How fast is your scope?  HP wrote the calibration to be used with a 54121T scope, which is a 20GHz scope.  The rise time of that scope can be ignored when adjusting something in the ns range.  It would start to be significant with a scope of 350MHz or less (general rule of thumb: Trise = 0.35 / BWscope).