Tektronix 2235 grief

B

BFoelsch

Guest
Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.

On both vertical channels, there is massive overshoot on rising edges
on the .1 v/cm ranges and higher. The lower voltage ranges are fine.

Poking around inside, I found a little assembly, P/N 307-1013-00 that
is labelled 10X and 100X . Apparently this assembly contains some
compensating capacitors for the attenuator.

In any event, touching this assembly, exerting the slightest force in
any direction clears up the problem, which quickly returns as soon as
I remove the pressure. I don't think the problem is the switch
contacts, as pressing down and wiggling the switch cam doesn't do
much.

Does this sound familiar? and what is the recommended fix. I hate to
start taking stuff apart "looking for trouble" so I figured I'd ask
here first. Or, if you have a manual/schematic of the input section
I'd appreciate that too.

Thanks to all in advance.
 
BFoelsch wrote:
Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.
Click to expand...
IMHO: gather your friends at the top of a tall building, toss this
"scope" as far as it will go.
 
BFoelsch <BFoelsch@comcast.ditch.this.net> wrote in
news:ju3sf29bov9mhpcuqm7d8uc5l315jhu5d4@4ax.com:

Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.

On both vertical channels, there is massive overshoot on rising edges
on the .1 v/cm ranges and higher. The lower voltage ranges are fine.

Poking around inside, I found a little assembly, P/N 307-1013-00 that
is labelled 10X and 100X . Apparently this assembly contains some
compensating capacitors for the attenuator.

In any event, touching this assembly, exerting the slightest force in
any direction clears up the problem, which quickly returns as soon as
I remove the pressure. I don't think the problem is the switch
contacts, as pressing down and wiggling the switch cam doesn't do
much.

Does this sound familiar? and what is the recommended fix. I hate to
start taking stuff apart "looking for trouble" so I figured I'd ask
here first. Or, if you have a manual/schematic of the input section
I'd appreciate that too.

Thanks to all in advance.
Click to expand...
Perhaps a bad solder joint at the pin/substrate interface?
Or a fractured SMD cap.
I believe regular solder will not work here,but don't have any
alternatives,either.Possibly some low-temp stuff like Chip-Quik may work
without destroying the metallization on the substrate.

The other alternative is to find a replacement thickfilm.
Sphere in Canada may have new parts for this,or cannabalize from a parts
scope.

(I always wondered if one could make a small PCB using SMD resistors and
caps instead of the ceramic thickfilm,to replace one of these.)

--
Jim Yanik
jyanik
at
kua.net
 
"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1157538586.561577.249600@p79g2000cwp.googlegroups.com:

BFoelsch wrote:
Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.

IMHO: gather your friends at the top of a tall building, toss this
"scope" as far as it will go.
Click to expand...
Bad advice;the 2235 was a good scope.

2*3*35 was a lousy scope,though,worthy of your advice.

--
Jim Yanik
jyanik
at
kua.net
 
Jim Yanik wrote:
"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1157538586.561577.249600@p79g2000cwp.googlegroups.com:


BFoelsch wrote:
Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.

IMHO: gather your friends at the top of a tall building, toss this
"scope" as far as it will go.


Bad advice;the 2235 was a good scope.
Click to expand...
Well, opinions will vary. In my somewhat limited (about 6) experience:

* The CRT is dim.

* The SMPS transformer screeches.

* A drop of Windex on the front panel and the 1-2-5 numbers on the
vertical controls come sliding off.

* There's often a burned PC board area under the cluster of 47 ohm
resistors. Guess they speced the resistors too small at 1/2 watt.

* The knobs feel loose and wiggly.

----
Personally I *love* the 2336 series. Much brighter CRT and sturdier
built than the 22xx series. If you can find one without a broken
hinge.
 
"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1157573045.045166.72120@m73g2000cwd.googlegroups.com:

Jim Yanik wrote:
"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1157538586.561577.249600@p79g2000cwp.googlegroups.com:


BFoelsch wrote:
Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.

IMHO: gather your friends at the top of a tall building, toss this
"scope" as far as it will go.


Bad advice;the 2235 was a good scope.

Well, opinions will vary. In my somewhat limited (about 6) experience:

* The CRT is dim.
Click to expand...
Basically the same tube as a 465.
Maybe whoever cal'd it didn't get the grid bias set right.

* The SMPS transformer screeches.
Click to expand...
Perhaps a bad xfmr? In my experience,few 2235's had that problem;I can't
recall any. Now the early 2213/2215's had that problem.
* A drop of Windex on the front panel and the 1-2-5 numbers on the
vertical controls come sliding off.
Click to expand...
I've encountered that too.

Probably after TEK outsourced their plastic parts production.
Somebody then got a "bright idea" to save money.
These days,I'd use some PC graphics program to print a clear decal to
replace the lettering.(those numbers would probably also run off with
Windex.)

* There's often a burned PC board area under the cluster of 47 ohm
resistors. Guess they speced the resistors too small at 1/2 watt.
Click to expand...
Vert output amp? If that's it,they changed it in the A model.(redesign)
I solved it by using a bit longer leads and some stand-off on the
replacements.

BTW,the PCB usually was not "Burned",just the solder mask discolored.
* The knobs feel loose and wiggly.
Click to expand...
Well,the 2200 series was meant to be low cost,not a lab scope,nor 465
quality.
BUT;
TEK sold a LOT of them.


----
Personally I *love* the 2336 series. Much brighter CRT and sturdier
built than the 22xx series. If you can find one without a broken
hinge.


Chock full of TEK-made ICs that aren't available anymore,and difficult to
Click to expand...
service.Also had a lot of HV failures. Attenuator problems,too.
I hated them.

BTW,the 2335 series was meant to be a "ruggedized" field-service
replacement for the 465.(that's why it's sturdier)
And TEK didn't sell many,except to the US military.


--
Jim Yanik
jyanik
at
kua.net
 
"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9836D4F64119Ejyanikkuanet@129.250.170.83...
"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1157573045.045166.72120@m73g2000cwd.googlegroups.com:


Jim Yanik wrote:
"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1157538586.561577.249600@p79g2000cwp.googlegroups.com:


BFoelsch wrote:
Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.

IMHO: gather your friends at the top of a tall building, toss this
"scope" as far as it will go.


Bad advice;the 2235 was a good scope.

Well, opinions will vary. In my somewhat limited (about 6) experience:

* The CRT is dim.

Basically the same tube as a 465.
Maybe whoever cal'd it didn't get the grid bias set right.


* The SMPS transformer screeches.

Perhaps a bad xfmr? In my experience,few 2235's had that problem;I can't
recall any. Now the early 2213/2215's had that problem.

* A drop of Windex on the front panel and the 1-2-5 numbers on the
vertical controls come sliding off.

I've encountered that too.

Probably after TEK outsourced their plastic parts production.
Somebody then got a "bright idea" to save money.
These days,I'd use some PC graphics program to print a clear decal to
replace the lettering.(those numbers would probably also run off with
Windex.)


* There's often a burned PC board area under the cluster of 47 ohm
resistors. Guess they speced the resistors too small at 1/2 watt.

Vert output amp? If that's it,they changed it in the A model.(redesign)
I solved it by using a bit longer leads and some stand-off on the
replacements.

BTW,the PCB usually was not "Burned",just the solder mask discolored.

* The knobs feel loose and wiggly.

Well,the 2200 series was meant to be low cost,not a lab scope,nor 465
quality.
BUT;
TEK sold a LOT of them.

Gee, I must have gotten the good one, the 2235 in question doesn't have ANY
Click to expand...
of the mentioned problems! I washed the front panel with "Mean Green" and it
looks like new, with all the lettering intact.

I did find the original problem. I did not realize that the attenuator
modules were in sockets! Pulling them out and cleaning up the pins solved
the problem.

It looks like an OK scope, definitely in the field service category. I am
truly amazed at how well the calibration has held up.

Thanks to all for your help.
 
Jim Yanik wrote:
BFoelsch <BFoelsch@comcast.ditch.this.net> wrote in
news:ju3sf29bov9mhpcuqm7d8uc5l315jhu5d4@4ax.com:

Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.
Click to expand...
Opt. 2 is AFAIR a change in the preregulator board (power supply).


Poking around inside, I found a little assembly, P/N 307-1013-00 that
is labelled 10X and 100X . Apparently this assembly contains some
compensating capacitors for the attenuator.

In any event, touching this assembly, exerting the slightest force in
any direction clears up the problem, which quickly returns as soon as
I remove the pressure. I don't think the problem is the switch
contacts, as pressing down and wiggling the switch cam doesn't do
much.
...snipp..
Perhaps a bad solder joint at the pin/substrate interface?
Or a fractured SMD cap.
I believe regular solder will not work here,but don't have any
alternatives,either.Possibly some low-temp stuff like Chip-Quik may work
without destroying the metallization on the substrate.

The other alternative is to find a replacement thickfilm.
Sphere in Canada may have new parts for this,or cannabalize from a parts
scope.
Click to expand...
I canibalized 7A18 that where otherwise unrepairable for these, or
unrepairable 465 scopes. The x10 and x100 ceramics were useful for me,
but of course it is some time effort necessary to bring parts in.


(I always wondered if one could make a small PCB using SMD resistors and
caps instead of the ceramic thickfilm,to replace one of these.)
Click to expand...
Was the method tof these times, Jim. You can find these a lot in
instruments of this age. Nowadays, when you look for the 0.002 ct
optimization, for a 60 to 100 MHz scope you would manufacture with PCB
made in China.


hth,
Andreas
 
"Andreas Tekman" <and7@bigfoot.com> wrote in
news:1157625938.592751.266170@p79g2000cwp.googlegroups.com:

Jim Yanik wrote:
BFoelsch <BFoelsch@comcast.ditch.this.net> wrote in
news:ju3sf29bov9mhpcuqm7d8uc5l315jhu5d4@4ax.com:

Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.



Opt. 2 is AFAIR a change in the preregulator board (power supply).
Click to expand...
I think you're wrong;IIRC,2235 had the pre-reg on the main board from the
beginning. It was early 2213/15 that had the Opt.48 pre-reg PCB added,as
the original triac pre-reg was noisy and failed a lot.
Poking around inside, I found a little assembly, P/N 307-1013-00 that
is labelled 10X and 100X . Apparently this assembly contains some
compensating capacitors for the attenuator.

In any event, touching this assembly, exerting the slightest force in
any direction clears up the problem, which quickly returns as soon as
I remove the pressure. I don't think the problem is the switch
contacts, as pressing down and wiggling the switch cam doesn't do
much.
..snipp..
Perhaps a bad solder joint at the pin/substrate interface?
Or a fractured SMD cap.
I believe regular solder will not work here,but don't have any
alternatives,either.Possibly some low-temp stuff like Chip-Quik may work
without destroying the metallization on the substrate.

The other alternative is to find a replacement thickfilm.
Sphere in Canada may have new parts for this,or cannabalize from a parts
scope.


I canibalized 7A18 that where otherwise unrepairable for these, or
unrepairable 465 scopes. The x10 and x100 ceramics were useful for me,
but of course it is some time effort necessary to bring parts in.
Click to expand...
Well,I confess I had a "senior moment";NOW I recognize the p/n given as the
common TEK hybrid attenuator modules used in 7K plug-ins and many 400
series scopes. DUH.....(smack forehead)

It's also possible that the module's pin sockets have some contamination or
have lost their grip.(like my memory!)
Perhaps a syringe injection of some alcohol would help here.
(I always wondered if one could make a small PCB using SMD resistors and
caps instead of the ceramic thickfilm,to replace one of these.)

Was the method tof these times, Jim. You can find these a lot in
instruments of this age. Nowadays, when you look for the 0.002 ct
optimization, for a 60 to 100 MHz scope you would manufacture with PCB
made in China.


hth,
Andreas
Click to expand...
Thanks for the help.

--
Jim Yanik
jyanik
at
kua.net
 
Jim Yanik wrote:
"Andreas Tekman" <and7@bigfoot.com> wrote in
news:1157625938.592751.266170@p79g2000cwp.googlegroups.com:
....snip...

Opt. 2 is AFAIR a change in the preregulator board (power supply).

I think you're wrong;IIRC,2235 had the pre-reg on the main board from the
beginning. It was early 2213/15 that had the Opt.48 pre-reg PCB added,as
the original triac pre-reg was noisy and failed a lot.
Click to expand...
hi jim, sorry when I did not make this point clearer in the posting.
You are absolutely right about the change from a triac pre-reg to the
MOSFET based prereg - as a later add-on, these unit got the
option-ident "opt. 48".

What I wanted to say that where even more chnages in the later 2235
scopes, that already where factory equipped with the MOSFET prereg.
AFAIR the later (or very late) changes where a "opt.2". But I am sorry,
I am unable to remember now if it was in the prereg, 2nd stage power
supply -- all is deep in my memo is the word power supply. Apologies if
my memory is wrong.

Poking around inside, I found a little assembly, P/N 307-1013-00 that
is labelled 10X and 100X . Apparently this assembly contains some
compensating capacitors for the attenuator.

In any event, touching this assembly, exerting the slightest force in
any direction clears up the problem, which quickly returns as soon as
I remove the pressure. I don't think the problem is the switch
contacts, as pressing down and wiggling the switch cam doesn't do
much.
..snipp..
Perhaps a bad solder joint at the pin/substrate interface?
Or a fractured SMD cap.
I believe regular solder will not work here,but don't have any
alternatives,either.Possibly some low-temp stuff like Chip-Quik may work
without destroying the metallization on the substrate.

The other alternative is to find a replacement thickfilm.
Sphere in Canada may have new parts for this,or cannabalize from a parts
scope.


I canibalized 7A18 that where otherwise unrepairable for these, or
unrepairable 465 scopes. The x10 and x100 ceramics were useful for me,
but of course it is some time effort necessary to bring parts in.

Well,I confess I had a "senior moment";NOW I recognize the p/n given as the
common TEK hybrid attenuator modules used in 7K plug-ins and many 400
series scopes. DUH.....(smack forehead)

It's also possible that the module's pin sockets have some contamination or
have lost their grip.(like my memory!)
Perhaps a syringe injection of some alcohol would help here.
Click to expand...
:)) No, injection to humans only makes the liver act faster, but you
loose the experience of the taste of the drink . I cannot recommend the
procedure ;-)


(I always wondered if one could make a small PCB using SMD resistors and
caps instead of the ceramic thickfilm,to replace one of these.)

Was the method tof these times, Jim. You can find these a lot in
instruments of this age. Nowadays, when you look for the 0.002 ct
optimization, for a 60 to 100 MHz scope you would manufacture with PCB
made in China.


hth,
Andreas



Thanks for the help.

--
Jim Yanik
Click to expand...
Always great to read here in the group about Tek scopes, I enjoy all
your contributions and knowledge. Thanks a lot too.


Andreas
 
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