Re: 454 screen brightness issues?


 

Jack:

Also, do you have a copy of a 454 manual?  I have a copy (070-0617-00; I
believe this is available "on the web" as a .pdf <possibly at
w140.com>); have you tried doing an initial setup of controls as
described on page 6-8 and 6-9  ("Preliminary Procedure"), followed by a
CRT Grid Bias adjustment (page 6-11) of grid bias potentiometer R1447
(shown on page 6-12), to get the voltage at TP1349 (shown on page 6-12)
to be at +12 volts with INTENSITY at mid-scale?  If the voltage at
TP1349 is too high (too much positive) it will result in very high
intensity which cannot be reduced to a workable value.  And if the
TP1349 voltage cannot be brought into range, this will (I think) mean
that your problem is likely in the Z-axis board area, so you won't have
to mess around with any of the HV resistors.

And if you find this to be the issue, keep us informed as to your
progress in repair.  I am interested because I have a 453A (sn b103169)
which has a similar problem (intensity is too high, and the 453A's
TP1047, which corresponds to the 454's TP1349, can only be adjusted to
values between about +35 to +75 volts) and I am starting to think it's a
Z-axis board issue.  The Z-axis circuitry in the 453A and 454 are very
similar.

Mike D. N4MWP

On 1/6/20 3:36 PM, Jack Ohme wrote:
Oh dear. The Z axis blanking doesnt seem to work either. Maybe this is a
grid issue after all

On Mon, Jan 6, 2020 at 11:55 AM Jack Ohme via Groups.Io <machinamancerjack=
gmail.com@groups.io> wrote:

Where should I be looking for those DC restorers, in the -1920v?

On Mon, Jan 6, 2020 at 11:52 AM Jack Ohme via Groups.Io <machinamancerjack=
gmail.com@groups.io> wrote:

Update:
Upon resistance testing the cathode and grid, it seems to want to conduct
one way (in negative resistance, according to my meter), and not conduct
at
all the other...
So perhaps the grid is not broken after all? Although this was with the
whole socket connected, so for all I know I could just be reading a diode
in the circuit, although the -10Mohm resistance would be odd for that.

On Mon, Jan 6, 2020 at 8:10 AM Chuck Harris <cfharris@...> wrote:

I saw that once in a 2456B's CRT. An internal weld between
a strap and an element broke, leaving an open circuit on
the CRT's intensity (control) grid .

The symptom was the intensity started out low, readout seemed
fine, and the beam could be moved with the intensity control,
but the beam kept getting brighter and brighter.

-Chuck Harris

Mlynch001 wrote:
I'm
wondering if maybe the grid assembly was knocked loose during
shipping
maybe? I'm not intimately familiar with the CRT construction, so
maybe
someone more well-acquainted with Tek's CRTs could give me some idea
of
what may be going on...
While fixing my newest 465 I recall seeing a post where a 465 had a
similar problem. The OP found an internally disconnected Grid pin.
Here
is the post.
https://groups.io/g/TekScopes/topic/tek_465_intensity_problem/7656664




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