Tektronix Oscilloscope 465B Problems

[ktl]

Just aquired an 465B Scope.

I have no sweep, just a wide dot when I press the beamfinder.

When I lower the timesetting I can see one single square wave, same on
both channels, It seems not to be affected by the settings on the Hor-
sensivity and the input selector is set to gnd.

Anyone that knows where to start.

[Ancient_Hacker]

Could be a switch setting problem. Try this:

Hook a wire from ch1 input to the calibrator loop.
Ch1 input selector to "AC", 0.1V/cm, var knob all the way clockwise
until it clicks. vert mode press ch1 only DOWN, all other buttons in
this column OUT.

Set the two Position knobs staright up.

Sweep speed: 5 ms/cm var knob all the way clockwise until it clicks.

"x10" button OUT
Intensity 3/4 of the way up.

Press sweep mode: Auto
Sweep source: "A"

Press trigger source: Ch1, internal
Trigger mode: normal, AC

Turn the trigger A knob to pointing straight up. The "trig" light
should go on, if it doesnt, turn the knob until it does. You won't be
able to see ANYTHING until you can get the TRIG light to light up.
Work on this first.

Press the beam finder. You should see a bright but small square wave.
Now use the horiz and vertical position knobs to center the square
wave on the screen. release the beam-finder button and you should
see about five cycles of a square wave. You might have to adjust the
intensity and focus knobs for best appearance.

[Jim Yanik]

"ktl" <k...@bornet.net> wrote in
news:1125576173.2...@g44g2000cwa.googlegroups.com:

I suggest you buy a service manual,and read the circuit description,it is
very detailed and VERY helpful.

another scope will be very useful in troubleshooting the sweep generators
and unblanking circuits where your problem could lie.
It may only be a CRT bias adjustment.

--
Jim Yanik
jyanik
at
kua.net

[ktl]

Finally solved it, 5 V supply was dead, due to a faulty filter cap.
Now it is working, but I guess that I need to do a complete check, what
I've seen is that the sweep starts one division below, then ramps up
very quickly, like within 1 to 2 subdivisions, and that there is some
sort of signal, even visible when inputs set for gnd.

[tekman]

Looks like there are even more of the voltages in the LV power supply
out of tolrance. Probably at least one more dry capacitor, or even
worse faults.

I'd recommend you download a complete service manual 8bama.sbc.edu or
bama.edebris.com) - you nee the Lizardtech browser to open the files,
but both (manual and browser are free of charge).

Then start to check the LV pwr supply carefully.

Looks like when you are through this, chances are good you have a nice
working scope.

hth,
Andreas

[ktl]

Got the manual, getting hold of another scope and a function-generator
and do a complete checkout.

The Lizardtech browserthing was a terrible experience, had to save each
schematic page (as well as other pages) as as bmp-file in order to
print it properly. No-one got it in pdf?

[tekman]

Well, since I had no problmes to view and print the document with the
Lizardtech browser - looks there is something unhappy with your pc or
it's setup.

Well, you might check the other free download sites
(www.teknetelctronics.com, etc.) for manuals. I am not up-to-date if
they have these things already.

Or buy a .pdf manual file from one of the sellers in the web.

It's of your choice ;-)

I hope your tek scope is doing fine now.

hth,
Andreas

[ktl]

Well the problem with the Lizardtech browser is that there is no
functions to do tiled printouts of the large pages, to get proper
printouts I'd finally had to export them to bitmap, and import them
into a photoeditor and then do a tiled printout.

[ktl]

I have been digging into my scope for some time, but there is one thing
I cant find, because the fault dissapears when the casing is removed,
seems to be heat related.

WHen the scope is powered up, both channels set for gnd, I can se a
stright fine line for each of the channels, but after som 5 minutes or
so the sweep is distorded, it sort of look like this:
_____________________________
I
\

The difference between the start of the sweep and the horizontal line
is about one div, if I try to write the sweep in XY coordinates it
looks something like this
Start 0.5,-1
start+1 0,-0.5
start+2 0,0
start+3 1,0
Then it is a straight line
This at 20ms
At 10 ms
It looks like this
_______________________________
I
I

And then the faster the sweep goes, the straighter line.

Now if anyone had any ideas where to start to look, so I could try to
heat up components carefully, to see which component that is failing. I
woild be grateful.

Best regards Tomas.

[Marcel Beysselance]

Mind to the big condensators in power supply. They are often dry. I had
to change both in my 3 scopes 465.

--
--
Marcel Beysselance

marcel.be...@hi-tek.fr
www.hi-tek.fr

[Jim Yanik]

Marcel Beysselance <bil...@msn.net> wrote in
news:43482b6a$0$455$7a62...@news.club-internet.fr:

PS filter Capacitors,electrolytics.

> in power supply. They are often dry. I had
> to change both in my 3 scopes 465.

They also can leak corrosive electrolyte onto the PCB,eating away copper
traces.

>
>

Power supplies should always be the first thing checked;voltage,ripple,AND
line regulation(VARIAC needed).

[ktl]

As it transpired, it was the Fan-motor assembly that caused the
problems. After some 5 mins, the fan stalled and was pulling near 400mA
from the +15 supply, not enough to shut it down, but enugh to disturb
other systems.
After changing the DIL14 quad transistor array, to normal BC557's
discrete (plugged into the DIL-socket) it seems to work like a charm.
Previously I did change all the filter-caps int pwr-sup, since they
were dead.
But I think that at the moment it seems to be ok, I will leave it on
now for a day or so, to see if the fix lasts.