On Wed, Jan 22, 2025 at 11:14?AM Sigur?ur ?sgeirsson via groups.io <siggi=
[email protected]> wrote:
On Wed, Jan 22, 2025 at 10:43?AM Sigur?ur ?sgeirsson via groups.io <siggi=
[email protected]> wrote:
Assuming this is calibrating something to do with the B sweep delay,
presumably you ought to be aligning two copies of the timing marks.
... on the bench scope ...
If you look at A1U850A, you'll see that DLY_REF_0 and _1 can both make
their way to the B-sweep DR (delay ref) pin, so presumably this is
calibrating out something to do with the alternate delay paths?
If you have the case off, you can verify this by looking at the control
signal on U850A while sitting at step (jj). If it's alternating, then the
two delay refs are being alternately routed to the B-sweep delay ref.
Note that since the control signal is under microcontroller-control, the
switching will be quite slow, so maybe you need to bump the persistence
on
your bench scope to see two instances of the time markers?
It occurs to me that alternatively you might be aligning the start time of
the B-sweep through two alternate paths. There is a mention in the ToO that
the B sweep can run concurrently with the A sweep, so perhaps the delay
reference is used to make sure the two sweeps are in time, whichever way
gates them.
... time passes ...
So I looked at the service manual for my 2467, which has essentially the
same instructions for step (jj), but it's only possible to route -1.25V or
the A-sweep delay reference to the B-sweep delay reference.
So, it's still possible that this is calibrating out something to do with
the two paths the B-sweep can be initiated. See page 3a-22, where it
discusses the BDCA signal. I could imagine alternating between the BDCA and
regular B delay sweep modes, adjusting the A and B delay reference voltages
in order to effectively measure the initiation delay of the B sweep through
the BDCA path.
Honestly, I just don't know. but again, if you probe the BDCA signal while
hanging out on the (jj) step, you'd be able to find out :).
And perhaps I'm just totally wrong, and this is simply calibrating the B
time base and/or delay:
/g/TekScopes/topic/2465b_vert_cal_02_cal_01/29871399.
Chuck will know this better than I do, and I don't pretend to offhand
understand how the +-B error thang works.
