Tek 465 oscilloscope

[Sidney]

Tektronix 100 Mhz dual channel oscilloscope model:Tek 465,year:1972
one day channel 1 trace disappeared but when you press beam finder
button the trace is on the top of the crt and while holding the beam
finder button in and moving the channel 1 vertical position pot up &
down the trace moves a bit but is still above on the crt screen,it is
visible on the top but not visible when the beam finder button is
released.I have the schematics but cannot figure it out.
Anyone have any common repair tips?.Thanks in advance.

Sidney
Dartmouth,Nova Scotia
Canada

 

[Richard Heindel]

Sidney,
Check the filter caps for the various low voltage supplies. I just had a similar problem but my trace
went off the left side of the screen and that ended up being bad caps on the +5v and -8v lines. If your
voltages are say, 2 volts or so low then you have a bad cap. If they are within say .25 volts then the trouble
is elsewhere. Check all the caps while your at it, you have 120V (with 110v, 55v, and 22v regulated off
that), +15V, +5V, and -8V. And make sure the schematics are for your serial number range. I was using the
power supply schematic for an earlier version and was fruitlessly trying to find a diode that no longer
existed.
Filter caps seem to be the number 1 failure item in the 465s.
Hope this helps.
Richard WB8KRN


"Sidney" <sidneybek@yahoo.com> wrote in message news:fecdbb87.0404291118.3e93d7fb@posting.google.com...

Tektronix 100 Mhz dual channel oscilloscope model:Tek 465,year:1972
one day channel 1 trace disappeared but when you press beam finder
button the trace is on the top of the crt and while holding the beam
finder button in and moving the channel 1 vertical position pot up &
down the trace moves a bit but is still above on the crt screen,it is
visible on the top but not visible when the beam finder button is
released.I have the schematics but cannot figure it out.
Anyone have any common repair tips?.Thanks in advance.

Sidney
Dartmouth,Nova Scotia
Canada

 

[Jim Yanik]

sidneybek@yahoo.com (Sidney) wrote in
news:fecdbb87.0404291118.3e93d7fb@posting.google.com:

Tektronix 100 Mhz dual channel oscilloscope model:Tek 465,year:1972
one day channel 1 trace disappeared but when you press beam finder
button the trace is on the top of the crt and while holding the beam
finder button in and moving the channel 1 vertical position pot up &
down the trace moves a bit but is still above on the crt screen,it is
visible on the top but not visible when the beam finder button is
released.I have the schematics but cannot figure it out.
Anyone have any common repair tips?.Thanks in advance.

Sidney
Dartmouth,Nova Scotia
Canada

Is Ch.2 doing the same,or is it OK?
If Ch.2 is OK,then first place I'd go is the input FET pair,look for a DC
offset on their output. The rest of the Ch.1 preamp is differential,so you
can pick places to short(collectors;voltage points,not current points) and
see if the trace centers.That will narrow it down to a particular stage.

If Ch.2 does the same as Ch.1,then the problem is in the output amp,a
different PCB.(the one the delay line goes to.)

--
Jim Yanik
jyanik-at-kua.net

 

[TekMan]

Jim Yanik <jyanik@abuse.gov> wrote in message news:<Xns94DAD5B4578DCjyanikkuanet@204.117.192.21>...

sidneybek@yahoo.com (Sidney) wrote in
news:fecdbb87.0404291118.3e93d7fb@posting.google.com:

Tektronix 100 Mhz dual channel oscilloscope model:Tek 465,year:1972
one day channel 1 trace disappeared but when you press beam finder
button the trace is on the top of the crt and while holding the beam
finder button in and moving the channel 1 vertical position pot up &
down the trace moves a bit but is still above on the crt screen,it is
visible on the top but not visible when the beam finder button is
released.I have the schematics but cannot figure it out.
Anyone have any common repair tips?.Thanks in advance.

Sidney
Dartmouth,Nova Scotia
Canada

Is Ch.2 doing the same,or is it OK?
If Ch.2 is OK,then first place I'd go is the input FET pair,look for a DC
offset on their output. The rest of the Ch.1 preamp is differential,so you
can pick places to short(collectors;voltage points,not current points) and
see if the trace centers.That will narrow it down to a particular stage.

If Ch.2 does the same as Ch.1,then the problem is in the output amp,a
different PCB.(the one the delay line goes to.)

I'd recommnd to follow the procedure Jim suggested.
And I would download a manual (e.g. the 475 from www.logsa.army.mil
or the 465B from bama.sbc.edu) of one of these similar instruments
(475/465B).

There is a "flowcart" in each of these servicemanuals that will very
well guide you through the process to analyze the cause of the error.

Even if the circuits & schematics are a bit different, the flowchart
is very well applicable to your 465.

hth,
Andreas