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--- 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.

...........................................

Your use of Yahoo! Groups is subject to

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

billw101@... wrote:

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

Hi Bill,

I would take a close look at the input FET's to make sure they are the
original type. Sometimes they will short or open and the repair techinician
will use whatever FET is handy and not bother with the correct part. This
can cause all sorts of oscillation problems and stuff like you are seeing.

Stan
w7ni@...

--- 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.

...........................................

Your use of Yahoo! Groups is subject to

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