old TEK 475 problem

[Jeffrey Dutky]

I've got an old TEK 475 that belonged to my father and hasn't seen the
light of day for at least ten years. I powered it up recently (after
'baking' it in the attic with a dehumidifier for a few weeks) and it
seems to be basically working, except for a little trouble with
channel 2:

When I connect channel 2 to the built-in calibration signal, rather
than the expected square wave, I get something that looks like this
(channel 1 is also
connected to the calibration signal):

_________ _________
| | | |
| | | | channel 1
| |_________| |_________



\ \
`-------- ,-------- `-------- ,-------- channel 2
/ /


I recognize this as an 'integrator' (Art of Electronics term) which, I
guess, means that there is a broken connection in the channel 2
electronics. Any ideas on where to start looking for the problem (or
if I'm on the wrong track, what I should be looking for)?

Another issue: I have two P6075A 10X probes for the scope, one of
which is marked "Bad". I haven't seen any difference in the readings
between the two probes (swapped on channel 1) but I've only been
looking at the, relatively low frequency, calibration signal. There
may be some obvious deficiency at high frequencies. Does anyone have a
suggestion where I could obtain another P6075A, or what other probe I
could use as a substitute?

-- Jeff Dutky

 

[Tweetldee]

I've got an old TEK 475 that belonged to my father and hasn't seen the
light of day for at least ten years. I powered it up recently (after
'baking' it in the attic with a dehumidifier for a few weeks) and it
seems to be basically working, except for a little trouble with
channel 2:

When I connect channel 2 to the built-in calibration signal, rather
than the expected square wave, I get something that looks like this
(channel 1 is also
connected to the calibration signal):

_________ _________
| | | |
| | | | channel 1
| |_________| |_________



\ \
`-------- ,-------- `-------- ,-------- channel 2
/ /


I recognize this as an 'integrator' (Art of Electronics term) which, I
guess, means that there is a broken connection in the channel 2
electronics. Any ideas on where to start looking for the problem (or
if I'm on the wrong track, what I should be looking for)?

Another issue: I have two P6075A 10X probes for the scope, one of
which is marked "Bad". I haven't seen any difference in the readings
between the two probes (swapped on channel 1) but I've only been
looking at the, relatively low frequency, calibration signal. There
may be some obvious deficiency at high frequencies. Does anyone have a
suggestion where I could obtain another P6075A, or what other probe I
could use as a substitute?

-- Jeff Dutky

Yep, you're thinking along the right path. The broken connection that
you're looking for is likely to be a tarnished or corroded vertical
sensitivity switch contact in channel 2. Take the covers off the scope so
you can get to the switch and see if you can get a cotton swab that has been
dipped in 91% isopropyl alcohol, or denatured alcohol. Be careful not to
get the common rubbing alcohol, because that may contain some contaminants
that you don't want to leave behind. Scrub the contacts until they are
bright and shiny. Actually, that's stretching it a bit.. just clean them
until the areas that make contact are clean and tarnish-free.
You might spray a cotton swab with a good tuner cleaner and CAREFULLY swab
it onto the contacts. Be very careful not to get any of the lubricant that
is in the tuner cleaner on the body of the switch. That's a pretty good
scope, and cleanliness is important in this area.
With a bit of care and luck, that should get your scope back into service.
Good luck!!
As for your probes, use Google to search for sources of used probes. I seem
to remember a web site that specializes in used probes, advertising
themselves as "dirt cheap probes" or something like that. Another great
source for probes is at a hamfest, the larger the better. Find one that's
scheduled within driving distance and visit. You'll probably find more than
probes to spend your cash on.
Cheers!!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Time is what keeps everything from happening all at once.

 

[Jim Yanik]

Yep, you're thinking along the right path. The broken connection that
you're looking for is likely to be a tarnished or corroded vertical
sensitivity switch contact in channel 2. Take the covers off the
scope so you can get to the switch and see if you can get a cotton
swab that has been dipped in 91% isopropyl alcohol, or denatured
alcohol. Be careful not to get the common rubbing alcohol, because
that may contain some contaminants that you don't want to leave
behind. Scrub the contacts until they are bright and shiny.
Actually, that's stretching it a bit.. just clean them until the
areas that make contact are clean and tarnish-free. You might spray a
cotton swab with a good tuner cleaner and CAREFULLY swab it onto the
contacts. Be very careful not to get any of the lubricant that is in
the tuner cleaner on the body of the switch. That's a pretty good
scope, and cleanliness is important in this area. With a bit of care
and luck, that should get your scope back into service. Good luck!!
As for your probes, use Google to search for sources of used probes.
I seem to remember a web site that specializes in used probes,
advertising themselves as "dirt cheap probes" or something like that.
Another great source for probes is at a hamfest, the larger the
better. Find one that's scheduled within driving distance and visit.
You'll probably find more than probes to spend your cash on.
Cheers!!!

Instead of using a cotton swab and getting cotton fibers wrapped around the
contacts,use a narrow strip of clean white paper,slide it under the closed
contact,then wet with a drop of alcohol(99% isopropyl).Then move the paper
srtip back and forth to clean the contact and pad.Tedious,but effective,and
you will not bugger up the contact fingers.Don't use tuner cleaner as some
will attack the polypropylene PCB material,and some tuner cleaners also
leave a lube film which is not good for TEK HF cam sw.contacts.(very low
wiping force)

I'm an ex-TEK service person,21.5 yrs with TEK.

 

[A E]

Instead of using a cotton swab and getting cotton fibers wrapped around the
contacts,use a narrow strip of clean white paper,slide it under the closed
contact,then wet with a drop of alcohol(99% isopropyl).Then move the paper
srtip back and forth to clean the contact and pad.Tedious,but effective,and
you will not bugger up the contact fingers.Don't use tuner cleaner as some
will attack the polypropylene PCB material,and some tuner cleaners also
leave a lube film which is not good for TEK HF cam sw.contacts.(very low
wiping force)

Hmmm, what about NU-TROL control cleaner? It's tetrafluoroethane. Cleans like a
champ, do you know if this can damage old Tek stuff? So far, it hasn't in my
careful use of the stuff.

 

[Rich Andrews]

[email protected] (Jeffrey Dutky) wrote in

I've got an old TEK 475 that belonged to my father and hasn't seen the
light of day for at least ten years. I powered it up recently (after
'baking' it in the attic with a dehumidifier for a few weeks) and it
seems to be basically working, except for a little trouble with
channel 2:

When I connect channel 2 to the built-in calibration signal, rather
than the expected square wave, I get something that looks like this
(channel 1 is also
connected to the calibration signal):

_________ _________
| | | |
| | | | channel 1
| |_________| |_________



\ \
`-------- ,-------- `-------- ,-------- channel 2
/ /


I recognize this as an 'integrator' (Art of Electronics term) which, I
guess, means that there is a broken connection in the channel 2
electronics. Any ideas on where to start looking for the problem (or
if I'm on the wrong track, what I should be looking for)?

Another issue: I have two P6075A 10X probes for the scope, one of
which is marked "Bad". I haven't seen any difference in the readings
between the two probes (swapped on channel 1) but I've only been
looking at the, relatively low frequency, calibration signal. There
may be some obvious deficiency at high frequencies. Does anyone have a
suggestion where I could obtain another P6075A, or what other probe I
could use as a substitute?

-- Jeff Dutky

For new probes, www.probemaster.com looks pretty good to me. I would think
that you could repair the one you have.

r

 

[Kevin Carney]

It could also be one of the compensation blocks that plug into the
attenuator. I belive they are marked 2X, 5X and 10X. They way to tell is
after doing the cleaning thing and if it doesn't fix the problem, swop the
attenuation blocks from the good to the bad channel. Do one block at a
time. Take Care, Kevin

--
change .combo to .com for correct email

***************************************************
"We ought always to know precisely why a given job
is done in a particular way, and why it is done at
all, and why it can't be done more efficiently,
if it must be done at all."-- T.J.Watson

***************************************************

 

[Jim Yanik]

Instead of using a cotton swab and getting cotton fibers wrapped
around the contacts,use a narrow strip of clean white paper,slide it
under the closed contact,then wet with a drop of alcohol(99%
isopropyl).Then move the paper srtip back and forth to clean the
contact and pad.Tedious,but effective,and you will not bugger up the
contact fingers.Don't use tuner cleaner as some will attack the
polypropylene PCB material,and some tuner cleaners also leave a lube
film which is not good for TEK HF cam sw.contacts.(very low wiping
force)

Hmmm, what about NU-TROL control cleaner? It's tetrafluoroethane.
Cleans like a champ, do you know if this can damage old Tek stuff? So
far, it hasn't in my careful use of the stuff.

I'm an ex-TEK service person,21.5 yrs with TEK.

IIRC,we were told to avoid using TFE on the atttenuator PCBs.Supposed to
cause microcracks in the substrate.

 

[JeffM]

\ \

`-------- ,-------- `-------- ,-------- channel 2
/ /


I recognize this as an 'integrator'
Jeffrey Dutky news:<[email protected]>

Actually, it's a differentiator (high-pass filter), which says that
the series capacitance is high in value (possibly open--totally capacitive)
when compared to the shunt element (resistor || capacitor).

 

[Jim Adney]

Yep, you're thinking along the right path. The broken connection that
you're looking for is likely to be a tarnished or corroded vertical
sensitivity switch contact in channel 2. Take the covers off the scope so
you can get to the switch and see if you can get a cotton swab that has been
dipped in 91% isopropyl alcohol, or denatured alcohol.

I'm not so sure this is good advice. I think this section of the 475
uses a very delicate cam switch which was only to be cleaned with pure
methanol. You also don't want to get cotton fibers in there; they
could stay behind and cause more problems, or snag the contacts and
ruin the switch. Don't take my advice on this, you should see if your
father had the 475 manual, because this will explain it all correctly.

There is something you CAN do right away. Rotate the vertical
sensitivity knob back and forth a few times just to see if this helps
at all. Move the AC-GND-DC switch back and forth a few times likewise;
it should be on DC for the test above. Any of these switch contacts
can get a bit of dust in there which could cause such a problem, so
it's useful to find out exactly where the problem is before you start
trying to clean things.

-

 

[Andy Cuffe]

It could also be one of the compensation blocks that plug into the
attenuator. I belive they are marked 2X, 5X and 10X. They way to tell is
after doing the cleaning thing and if it doesn't fix the problem, swop the
attenuation blocks from the good to the bad channel. Do one block at a
time. Take Care, Kevin

I was able to repair a bad attenuator block on one of my Tek scopes by
resoldering the connections to the ceramic substrate. The plastic cover
on the attenuator was easily removable. I'm not sure if the 475 uses
the same type. In this case it was only some V/div that didn't work.
If all settings aren't working I doubt it could be a bad attenuator.

 

[Lionel]

I'm an ex-TEK service person,21.5 yrs with TEK.

I don't suppose you've got any tips on where I can obtain
(electronically, if possible) a user manual & a service manual for my
fantastic old Tek 2235 CRO?
(It hasn't been calibrated in the 10 years I've owned it, but it still
works beautifully!)

 

[Jim Yanik]

I don't suppose you've got any tips on where I can obtain
(electronically, if possible) a user manual & a service manual for my
fantastic old Tek 2235 CRO?
(It hasn't been calibrated in the 10 years I've owned it, but it still
works beautifully!)

First,Ebay.
Also;
MANUALS SOURCES

TECH SYSTEMS 1-800-435-1516
SYNERGETICS SURPLUS 520-428-4073
PEPPER SYSTEMS 214-353-0257
MANUALS PLUS 206-531-8031
US SURPLUS 410-750-1083
E-MAIL: [email protected]

Tektronix Used Manual Sources:
1. Deane Kidd 27270 SW Ladd Hill Road Sherwood, OR 97140, 503 625-
7363
(also has some parts)
2. Ed Matsuda, P.O. Box 390613, San Diego, CA 92149, 619 479-0225
voice, 619 479-1670 fax
3. Manual Merchant: Linda Perkins, PO Box 927792 San Diego CA 92192,
619-642-0785, -0885 fax, [email protected]
4. W7FG Vintage Manuals, 3300 Wayside Dr., Bartlesville, OK 74006,
800-807-6146
5. Manuals Plus, P.O. Box 549, TAD #601, Tooele, Utah 84074, (801)
882-7188, (801) 882-7195 Fax

Some of these may be out of date.

 

[JeffM]

(electronically, if possible) a user manual & a service manual

Jim Yanik

1st place I'd look is Tom Gootee (dead tree)
http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=gootee+manuals&btnG=Google+Search

 

[KLØS]

Try:

http://www.logsa.army.mil/etms/find_etm.cfm

search "TM Title" for "tektronix" and scroll down to find the manual you're
looking for.

Dino KLØS/4

 

[KLØS]

I tried replying to the Grantl who asked for additional info but after
removing the "NOSPAM" part of your address it still bounced. So here's the
info on getting to the site:

----------
Grant-- try going first to:

http://www.logsa.army.mil/

Select "Publications and Forms"

which should get you to:

http://www.logsa.army.mil/pubs.htm

then select "Electronic Technical Manuals Online"

which will roll you down to:

"Go to Electronic Technical Manuals Online" - click on this link which
takes you to:

http://www.logsa.army.mil/etms/online.htm

If you accept their terms click on "I accept" which takes you to:

http://www.logsa.army.mil/etms/welcom1.htm

Choose "Enter the Site" [Note the disclaimer that you have to login if
accessing anything but public release manuals and that you have to have 128
bit encryption engaged. That should bring you to:

http://www.logsa.army.mil/etms/find_etm.cfm

which is the search page; click on "TM Title Text" and enter "tektronix" and
scroll down to hit "search" which should get you to:

http://www.logsa.army.mil/etms/show_etm.cfm

where if you scroll down and look CAREFULLY you'll find Tek 475 material
which you can then download (it's in .pdf format).

You may have to go thru this entire process to establish the fact that you
accept their terms....there's probably a cookie in my system that lets me go
straight to the search page. I've found a number of good references here
for text equipment.

Let me know if you have any luck...

Dino KLØS/4