Re: 465 Display Help Needed - another thought


Bill Wollam
 

--- In TekScopes@y..., ashtonb@j... wrote:
--- In TekScopes@y..., Kurt Graber <kurtg@s...> wrote:


billw101@a... wrote:

Hello, I have been pulling problems out of a 465 that I recently
acquired. The last remaining problem is the inability to get a
sharp
focus on the trace with any combination of intensity, focus or
astigmatism. I have checked everything in the CRT circuits with
the
exception of the high voltage, crt bias and cathode bias, until
I
get
the use of an HV probe. Can anyone tell me if I am looking in
the
right area or suggest any common failure modes? The low voltage
supplies all check good and noise free. Thanks for any help.
...........................................



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A common problem or failure is the opening of the voltage divider
circuit
that the focus and astig tap into.
I am unfamilier with your particular scope but the chances are
good
that one
of the resistors has opened up. I have seen many cases !!! you
don't
need a
HV probe , just take your meter and ohm them out. They will not
appear burned
but they have a tendancy to open up due to the high
voltage.......this will
cause an unsharp trace and many cases no trace at all (just a
haze)...Good
Luck
Another point: the 46x, 47x series just wasn't as sharp as the tube
scopes! or even and especially - the 454, 454A. Some engrs. think
the 454A best 150 MHz scope ever (2mV/DIV, all the delay
triggering)
or sometimes ~ 200 MHz if all went well on that assembly..

I can see the clear difference bewtween say, a 475A and the 454As
-
tiny wiggles just visible on 54-A disappear into the thick trace of
475 (or 465).

Just in case you're trying to do better than it Can!


Ashton
AShton, yes I have heard that same thing about the 465, however after
troubleshooting I am further able to describe the problem. The
transition of the trace either falling or rising is poorly defined
and instead of one sharp edge I see almost a centimeter of blur. I
have been through the video output amplifier from one end to the
other but I still have the symptom that any capacitance such as a
scope lead hung on either vertical deflection output causes the
amplifier to go into high freq. oscillation and the trace becomes a
fog. I will press on but there is definitely something wrong with
this thing.

Bill

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