jgray at zianet.com
Sat Oct 10 18:42:29 UTC 2009
I did your test and at the 12 o'clock position, both levels read
-0.32V. Zero volts is at about 1 o'clock. With the attenuator switched
in, the range on the pots is fairly sharp.
Thanks for the tip. I'll add the DC bias adjustment to my list.
On Sat, Oct 10, 2009 at 8:57 AM, Greg Burnett <gbusg at comcast.net> wrote:
> Here's a coarse way to use the front panel to see if any large DC bias
> errors have developed in your Input Amp and/or Schmitt Trigger circuits (A3
> and A4) for either or both channels. (Disclaimer: this doesn't replace the
> corresponding DC bias adjustments in the manual, but it is a quick way to
> observe the symptoms that get progressively worse when either an Input Amp
> or Schmitt Trigger I.C. are beginning to go bad.)
> For each input channel (and while watching its "Trigger" LED) manually
> rotate its "Level" pot back and forth, putting the pot in the center of the
> range in which the "Trigger" LED repetitively blinks. At this pot position,
> your displayed "Trigger Level" should be close to zero volts and the knob's
> pointer should be pointing approximately straight up (12 o'clock position).
> For this test you want just barely enough input signal so that there's a
> very narrow, "exact" setting of the "Trigger Level" pot that produces
> Assuming you're using the 5370A's timebase output as the source - and to
> make it easier to "eyeball" the center of trigger range - configure your
> inputs for:
> Start Com
> 50 ohm Input
> Divide by 10 attenuation
> For each channel, if triggering is centered near zero volts (say, +/-
> 0.03V), that's a good sign. However, if triggering centers at a larger DC
> offset, that may be a sign of trouble in an Input Amp and/or Schmitt
> Trigger. Small errors may be adjusted-out via their respective DC bias
> adjustments. However as the I.C.s continue to deteriorate, there comes a
> time when the only solution is to replace the bad I.C.(s).
> Hopefully your unit isn't so afflicted. ...Just covering the bases...
> ----- Original Message -----
> From: "Joseph Gray" <jgray at zianet.com>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Sent: Saturday, October 10, 2009 3:14 AM
> Subject: Re: [time-nuts] 5370A
> Trigger levels are set to "Preset" for most steps. In step 18, I
> verified that Preset is 0V and the Level voltage varied from
> aproximately -1.3 to +0.6 volts. The manual specifies "approximately
> -1.3 to +0.5 volts."
> In step 15, the standard deviation was bouncing around between about
> 36-57pS. The manual says that less than 100pS is good.
> Time for bed.
> Joe Gray
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