Hi Fabio,
Firstly, thank you for giving this some thought. Some of my observations:
1. Check STORAGE WINDOW Operation. This all works fine, except that when going to "d. set STORAGE WINDOW PRE TRIG" the triggering jitter becomes quite noticeable; it is less so in POST TRIG.
2. Check A and B+ GATES.
Set NON-STORE On; A TIME/DIV 0.1 ms; B TIME/DIV 20 us. All works as expected, except for the jitter when in NORM storage mode - Non-storage there is a rock-solid trace with no jitter at all.
3. Check/Adjust Storage NORM Trigger DC Balance (R126)
Set CH1 VOLTS/DIV 5mV; HORIZ DISPLAY A. Remember that the A sweep is still at 0.1 ms/DIV and so there are some 50 full cycles of a 50-kHz sine-wave. Trying to set anything with the A TRIGGER LEVEL is nigh on impossible. I think the sweep should be A at 20 us/DIV, showing ten full cycles. The problem now is that trying to align the leading edge with the second vertical graticule line at the horizontal centre graticule line results in loss of triggering. This alignment can be done using the horizontal position control, however. When aligned in this way, switching between AC and DC Trigger coupling of the A sweep shows no movement.
Have I achieved what is required, or am I again missing something?
It is a pity that Reed Dickinson hasn't seen this thread, as I think he is a bit of an expert on the 468 and he certainly holds them in some respect. However, I repeat my thanks to you, Fabio.
Regards, Colin.
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Fabio Trevisan Sent: 05 July 2018 17:09 To: [email protected]Subject: Re: [TekScopes] 468 DSO Calibration/troubleshooting Hello Collin, Regarding my last statement (the P.S.), that this check should be made in "non-store" mode, I'm giving second thoughts at it. I`m not sure yet, but I just found out that there are two "NORM triggering DC balance" adjustments... one on the analog side and another one on the storage side... So, it seems weird that we could even be able to adjust the STORAGE NORM triggering DC balance in any mode that isn't a storage mode. On the other hand, I may still be correct on my initial assumption, because the flow of the instructions and the explicit instruction to set "NON STORE" to ON, at Section #2, step g. I`m only not sure if that adjustment (R126) would be even doable while in NON STORE mode... I`ll get back to it as soon as I can dig a little bit more on the manual. Rgrds, Fabio On Thu, Jul 5, 2018 at 08:23 am, Fabio Trevisan wrote:
Hello Colin,
I don't own a 468 and have no particular experience with it, but I have the
manuals (in PDF form) and since your doubt is related to understaing of the
instructions, I decided to give it a try and see if I could make sense out of
this part of the instruction that you're doubtful at.
At this step, the only thing that doesn't seem really clear to me is why it
asks specifically to align the leading edge of the sine-wave to the 2nd
graticule line (why the 2nd.???)..
But, regardless of not understanding that, I think the purpose of this
calibration step is clear... Is to make a "differential" assessment of the
triggering level shift, between using AC triggering coupling and DC triggering
coupling...
So, basically what it is asking for, is for you to make sure that the
triggering point doesn't move between AC and DC coupling, when you're actually
feeding a signal that already swings about 0V...
I mean, if the input signal is swinging about 0V (i.e. if it doesn't contain a
DC level), changing the triggering coupling from AC to DC should not make any
difference, and therefore, the triggering point, whatever it was set to before
switching to DC, the wave form must remain in the same position.
If the waveform shifts horizontally, than it means that the triggering point
"seen" by the triggering circuit have changed when switching over from AC to
DC, which it shouldn't.
Giving second thoughts to the instruction, it's not much different than
adjusting the Norm DC triggering balance of a 464 (which I own), and probably
the same as the 465 (more common).
the only difference is that, for the 464, we're asked for looking at the very
beginning of the sweep, and not at the 2nd vertical graticule line (i.e. 1
division after the sweep actually started).
This difference in procedure (from the non store scope), doesn't actually
matter to what the DC balance adjustment is doing (which is nothing more than
shifting the DC level of the actual signal being fed to the triggering input
buffer, with the intent to making it match with the level of the same signal
when AC coupled).
The only reason I think they're doing that (adjusting at the 2nd vertical
graticule line iso at the beginning of the sweep), is because this point is
about the actual point on the display where the triggering point of the
digital stored signal is supposed to be displayed.
P.S. Also note that, although this adjustment step is called "Check / Adjust
STORAGE NORM Trigger DC balance", by following the instructions coming from
the previous steps, I understand (it's my conclusion though) that this
adjustment is not meant to be performed in storage mode.
The previous section, "#2 Check A and B+ gates", at step g. it asks you to
set the "NON STORE" button to ON position... and then it doesn't ever ask you
to change it to OFF, so, by the flow of the procedure, the #3 check is to be
performed in NON STORE mode.
Therefore, this jitter that you mentioned you're getting on storage mode
should not interfere with you performing this adjustment (because it's done in
NON STORE mode).
Now, talking about this jitter... I don't think it has any relation to this
adjustment, and it's probably not going to be fixed by setting this adjustment
right.
I hope I was able to help you somehow.
KRgrds,
Fabio
On Tue, Jul 3, 2018 at 10:08 am, Colin Herbert wrote:
I have got through the calibration/adjustment procedure up to "Storage
Triggering". My problems now are twofold. I can't understand Section #3 -
"Check/Adjust Storage NORM Trigger DC Balance" (P4-89 in the manual). Apart
from the fact that the storage triggering has a deal of jitter, I can't get
step (e) to make sense. I am supposed to "use the A TRIGGER LEVEL to align
the
point where the sine-wave's leading edge intersects the center horizontal
graticule line with the 2nd vertical graticule line". Because of the the
jitter and the fact that the triggering fails when I adjust the A TRIGGER
LEVEL, this is impossible. Am I doing something wrong (quite possible), or is
the manual giving me the wrong information? Help!
If anyone has an idea of how I can eliminate the jitter, that would be nice,
too. There is no jitter in "NON STORE" operation. I was hoping it would just
be something simple like a switch needing cleaning, or an IC needing
reseating, but nothing has given me any clues so far...
Colin.
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