[time-nuts] 5370A

[Greg Burnett]

Joe,

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 
triggering.

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...

Best,
Greg



----- 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


John,

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
KA5ZEC