Re: Tek 2467B Erratic Intensity controls


Chuck Harris <cfharris@...>
 

Hi Peter,

About the display counter.

I think there is a bug in the software that makes the counter
count twice. If you wait long enough, the screen will blank.

I have seen this behavior on every 2467B that has come my way.

It counts 16M-->0, and then counts 16M-->0 and blanks.

You can determine the counter's behavior by looking at the
various EXER routines in the diagnostics menu. I don't recall
which routine it is, but it is listed in the manual.

-Chuck Harris

peter bunge wrote:

Thanks Chuck;
however I bought the U800 to repair a friend's 2465 scope that was sitting
on a shelf with the feet overhanging so the cooling holes in the bottom of
the 'scope were blocked. This may not have been the cause but the 'scope
failed suddenly.
My present problem with a 2467B S/N B051193 has nothing to do with U800 but
may be associated with U650. I mentioned the problems as general interest.
The symptoms are that changes in either of the intensity pots takes
several, and up to many (30 or more), seconds to respond either in
intensity on the screen, or voltages at the sequencer pins. Without
touching anything on the 'scope the 'trace turn off' counts down from
minutes, to 59 seconds, down to 2 seconds, then starts again at (8) minutes
without shutting off the display. So that feature is not working. At very
bright it did drop the intensity after 30 seconds but did not turn it off
so it may be partly working. I remember it turned the displays off until a
knob was moved.
Delta v and delta t are erratic placing the dotted lines on the screen, and
dt sometime shows dv lines or nothing. And they have the same sluggish
delay to doing anything.
The 5 capacitors have been professionally replaced before I got the 'scope
and they look good. There could still be corrosion somewhere but I don't
intend to replace them haphazardly without some evidence. I washed around
them by brushing Isopropyl Alcohol and letting it run down onto paper
towel. There is no evidence of a change. I don't think they are the problem.
I re-soldered the legs of the coil and saw no change, not that I expected
to.
I was following the troubleshooting (page 458 in several pdfs) that asks if
the LEDs respond to "A/B Trig" being pressed. This is confusing since they
don't define 'respond'. Fortunately I have a 2465 with Tek manual which
asks the same thing. On the 2465 the displays are switched each
press/release but on my 2467B they change back when released. Is this
normal? Another problem is that if I go to 4 as directed it asks about
"signals conforming to guidelines at the left" and that page is missing or
out of order in the pdf. My 2465 Tek manual shows the page I should see.
However with my new interpretation of 'respond' I was being led astray so
the answer should have been 'no' and I should not have gone to 4. The next
step is "do scale factors appear with readout intensity full cw?" Yes takes
me to "repair LED or front panel interconnect", unlikely, so this takes me
nowhere.
I swapped sequencer U650 155-0244-01 with 155-0244-00 from the 2465 but
there was no change.
Still struggling but getting a better understanding. Time to 'scope around
the circuits.
Peter

On Sun, Dec 1, 2019 at 12:42 PM Chuck Harris <cfharris@erols.com> wrote:

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