Tektronix 2235 Intensity issue

J

John B

Guest
Recently purchased a Tek 2235 (does not have military option). It displays
both traces ok as well as a square wave on both channels. Both traces
respond to the 'A' intensity control, while the 'B' intensity control has no
effect. Has anyone else experienced this problem? Both the 'A' & 'B'
intensity control pots check out ok. Voltage at the base of Q814 varies when
the 'B' pot is turned as well as the output voltage on the emitter of Q814.
Voltages here are correct too. There is no voltage change at the node of
anodes CR818 and CR820 while turning the 'B' pot, but it does change here
when the 'A' intensity pot is turned. I've checked all related
diodes --CR818, CR820, CR805, CR817, CR816, CR680, etc., and related
resistors. Q586 is biased and stays on in "Ch1", "CH2", and "Both"
positions, at least as far as I can tell with the voltmeter. I don't see
any components with visible damage, but there is a place on the board that
is brown from heat around Q254, Q255, Q256 which is the Vertical output to
CRT section. I'm guessing that this is unrelated to the intensity problem.
any help or ideas would be greatly appreciated.

Thanks,
John
 
"John B .att.net>" <robotwizard@<removethis> wrote in message
news:VTTXb.5498$aH3.177125@bgtnsc04-news.ops.worldnet.att.net...
Recently purchased a Tek 2235 (does not have military option). It displays
both traces ok as well as a square wave on both channels. Both traces
respond to the 'A' intensity control, while the 'B' intensity control has
no
effect. Has anyone else experienced this problem? Both the 'A' & 'B'
intensity control pots check out ok. Voltage at the base of Q814 varies
when
the 'B' pot is turned as well as the output voltage on the emitter of
Q814.
Voltages here are correct too. There is no voltage change at the node of
anodes CR818 and CR820 while turning the 'B' pot, but it does change here
when the 'A' intensity pot is turned. I've checked all related
diodes --CR818, CR820, CR805, CR817, CR816, CR680, etc., and related
resistors. Q586 is biased and stays on in "Ch1", "CH2", and "Both"
positions, at least as far as I can tell with the voltmeter. I don't see
any components with visible damage, but there is a place on the board that
is brown from heat around Q254, Q255, Q256 which is the Vertical output to
CRT section. I'm guessing that this is unrelated to the intensity problem.
any help or ideas would be greatly appreciated.

Thanks,
John
Click to expand...
John
You didn't mention whether you were using the B timebase for your tests, the
B intensity control only affects the traces on the B timebase.
Martin

--
martin<dot here>whybrow<at here>ntlworld<dot here>com
 
Put the horizontal mode in ALT, pull the outer time base knob (B sweep) and
turn a few clicks to the right. Now you will have two seperate sweeps and
they should be seperatable (vertically) with the A/B SWP SEP control. Turn
the B Delay Time Position control and the intensified sweep should move
across the screen.

--
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

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

"John B .att.net>" <robotwizard@<removethis> wrote in message
news:VTTXb.5498$aH3.177125@bgtnsc04-news.ops.worldnet.att.net...
Recently purchased a Tek 2235 (does not have military option). It displays
both traces ok as well as a square wave on both channels. Both traces
respond to the 'A' intensity control, while the 'B' intensity control has
no
effect. Has anyone else experienced this problem? Both the 'A' & 'B'
intensity control pots check out ok. Voltage at the base of Q814 varies
when
the 'B' pot is turned as well as the output voltage on the emitter of
Q814.
Voltages here are correct too. There is no voltage change at the node of
anodes CR818 and CR820 while turning the 'B' pot, but it does change here
when the 'A' intensity pot is turned. I've checked all related
diodes --CR818, CR820, CR805, CR817, CR816, CR680, etc., and related
resistors. Q586 is biased and stays on in "Ch1", "CH2", and "Both"
positions, at least as far as I can tell with the voltmeter. I don't see
any components with visible damage, but there is a place on the board that
is brown from heat around Q254, Q255, Q256 which is the Vertical output to
CRT section. I'm guessing that this is unrelated to the intensity problem.
any help or ideas would be greatly appreciated.

Thanks,
John
Click to expand...
 
Thanks for the suggestions. As you can probably tell it's been awhile, and a
different scope on top of that. Nothing like chasing a fault that doesn't
even exist. :)
The 2235 has a lot of nice features. I think I will like it once I get more
familiar with the triggering etc.



"Kevin Carney" <carneyke@us.ibm.combo> wrote in message
news:c0r0tc$nvc$1@news.btv.ibm.com...
Put the horizontal mode in ALT, pull the outer time base knob (B sweep)
and
turn a few clicks to the right. Now you will have two seperate sweeps and
they should be seperatable (vertically) with the A/B SWP SEP control. Turn
the B Delay Time Position control and the intensified sweep should move
across the screen.

--
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

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

"John B .att.net>" <robotwizard@<removethis> wrote in message
news:VTTXb.5498$aH3.177125@bgtnsc04-news.ops.worldnet.att.net...
Recently purchased a Tek 2235 (does not have military option). It
displays
both traces ok as well as a square wave on both channels. Both traces
respond to the 'A' intensity control, while the 'B' intensity control
has
no
effect. Has anyone else experienced this problem? Both the 'A' & 'B'
intensity control pots check out ok. Voltage at the base of Q814 varies
when
the 'B' pot is turned as well as the output voltage on the emitter of
Q814.
Voltages here are correct too. There is no voltage change at the node of
anodes CR818 and CR820 while turning the 'B' pot, but it does change
here
when the 'A' intensity pot is turned. I've checked all related
diodes --CR818, CR820, CR805, CR817, CR816, CR680, etc., and related
resistors. Q586 is biased and stays on in "Ch1", "CH2", and "Both"
positions, at least as far as I can tell with the voltmeter. I don't
see
any components with visible damage, but there is a place on the board
that
is brown from heat around Q254, Q255, Q256 which is the Vertical output
to
CRT section. I'm guessing that this is unrelated to the intensity
problem.
any help or ideas would be greatly appreciated.

Thanks,
John
Click to expand...
 
"John B" <robotwizard@removethis.att.net> wrote in
news:ifdYb.9101$aH3.303896@bgtnsc04-news.ops.worldnet.att.net:

Thanks for the suggestions. As you can probably tell it's been awhile,
and a different scope on top of that. Nothing like chasing a fault
that doesn't even exist. :)
The 2235 has a lot of nice features. I think I will like it once I get
more familiar with the triggering etc.
Click to expand...
It's a good scope.Watch out for the focus resistor string,it has a tendency
for the carbon film resistors to increase in value until they open.Replace
with carbon comp resistors,same value and wattage(1/2w.)
Other than that,main failures are bad electrolytics and shorted rectifier
diodes. One more item;the pre-reg FET should be slodered to the 3 wire
ribbon cable,the Molex would overheat and char,causing FET failure.If you
still have the Molex,if it's beginning to discolor,cut it off and solder
the wires direct to the FET leads.(this was a TEK official mod;to remove
the Molex,but may not have been performed on every scope.)


--
Jim Yanik
jyanik-at-kua.net
 
"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9491D058853EEjyanikkuanet@204.117.192.21...
"John B" <robotwizard@removethis.att.net> wrote in
news:ifdYb.9101$aH3.303896@bgtnsc04-news.ops.worldnet.att.net:

Thanks for the suggestions. As you can probably tell it's been awhile,
and a different scope on top of that. Nothing like chasing a fault
that doesn't even exist. :)
The 2235 has a lot of nice features. I think I will like it once I get
more familiar with the triggering etc.



It's a good scope.Watch out for the focus resistor string,it has a
tendency
for the carbon film resistors to increase in value until they open.Replace
with carbon comp resistors,same value and wattage(1/2w.)
Other than that,main failures are bad electrolytics and shorted rectifier
diodes. One more item;the pre-reg FET should be slodered to the 3 wire
ribbon cable,the Molex would overheat and char,causing FET failure.If you
still have the Molex,if it's beginning to discolor,cut it off and solder
the wires direct to the FET leads.(this was a TEK official mod;to remove
the Molex,but may not have been performed on every scope.)


--
Jim Yanik
jyanik-at-kua.net
Click to expand...
Thanks for the advice Jim. I pulled the plastic cover off the bottom of the
main board and sure enough the board is discolored where the focus resistors
are mounted. I found the FET regulator , mine has 3 separate wires as
opposed to the ribbon cable you mentioned, but it does have the Molex
connector which appears to be in good shape-- at least it hasn't discolored
yet. Any thoughts on what could cause the discoloration on the board around
the vertical output under the CRT?

Thanks,
John
 
Anybode has schematics for this Tek 2235 scope?

Harm


"John B" <robotwizard@removethis.att.net> wrote in message news:<CVEYb.14314$aH3.471951@bgtnsc04-news.ops.worldnet.att.net>...
"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9491D058853EEjyanikkuanet@204.117.192.21...
"John B" <robotwizard@removethis.att.net> wrote in
news:ifdYb.9101$aH3.303896@bgtnsc04-news.ops.worldnet.att.net:

Thanks for the suggestions. As you can probably tell it's been awhile,
and a different scope on top of that. Nothing like chasing a fault
that doesn't even exist. :)
The 2235 has a lot of nice features. I think I will like it once I get
more familiar with the triggering etc.



It's a good scope.Watch out for the focus resistor string,it has a
tendency
for the carbon film resistors to increase in value until they open.Replace
with carbon comp resistors,same value and wattage(1/2w.)
Other than that,main failures are bad electrolytics and shorted rectifier
diodes. One more item;the pre-reg FET should be slodered to the 3 wire
ribbon cable,the Molex would overheat and char,causing FET failure.If you
still have the Molex,if it's beginning to discolor,cut it off and solder
the wires direct to the FET leads.(this was a TEK official mod;to remove
the Molex,but may not have been performed on every scope.)


--
Jim Yanik
jyanik-at-kua.net

Thanks for the advice Jim. I pulled the plastic cover off the bottom of the
main board and sure enough the board is discolored where the focus resistors
are mounted. I found the FET regulator , mine has 3 separate wires as
opposed to the ribbon cable you mentioned, but it does have the Molex
connector which appears to be in good shape-- at least it hasn't discolored
yet. Any thoughts on what could cause the discoloration on the board around
the vertical output under the CRT?

Thanks,
John
Click to expand...
 
"John B" <robotwizard@removethis.att.net> wrote in
news:CVEYb.14314$aH3.471951@bgtnsc04-news.ops.worldnet.att.net:

"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9491D058853EEjyanikkuanet@204.117.192.21...
"John B" <robotwizard@removethis.att.net> wrote in
news:ifdYb.9101$aH3.303896@bgtnsc04-news.ops.worldnet.att.net:

Thanks for the suggestions. As you can probably tell it's been
awhile, and a different scope on top of that. Nothing like chasing
a fault that doesn't even exist. :)
The 2235 has a lot of nice features. I think I will like it once I
get more familiar with the triggering etc.



It's a good scope.Watch out for the focus resistor string,it has a
tendency
for the carbon film resistors to increase in value until they
open.Replace with carbon comp resistors,same value and wattage(1/2w.)
Other than that,main failures are bad electrolytics and shorted
rectifier diodes. One more item;the pre-reg FET should be slodered to
the 3 wire ribbon cable,the Molex would overheat and char,causing FET
failure.If you still have the Molex,if it's beginning to discolor,cut
it off and solder the wires direct to the FET leads.(this was a TEK
official mod;to remove the Molex,but may not have been performed on
every scope.)


--
Jim Yanik
jyanik-at-kua.net

Thanks for the advice Jim. I pulled the plastic cover off the bottom
of the main board and sure enough the board is discolored where the
focus resistors are mounted. I found the FET regulator , mine has 3
separate wires as opposed to the ribbon cable you mentioned, but it
does have the Molex connector which appears to be in good shape-- at
least it hasn't discolored yet. Any thoughts on what could cause the
discoloration on the board around the vertical output under the CRT?

Thanks,
John
Click to expand...
Those vertical resistors DO get pretty hot.I can't recall any problems with
them,though. You could put new ones in and raise them off the board a
little bit.

--
Jim Yanik
jyanik-at-kua.net
 
Tektronix isn't able to provide support, and I am in need of a service
manual for this scope. Or advice on how to get the printer interface to
recognize the printer. The same printer and cable combination works on
several other Tektronix 2235 scopes, so I'm sure this one has a problem.

Thanks
 
Richard Henne <Rich.Henne@asu.edu> wrote in message news:<c12npu$ei6$1@news.asu.edu>...
Tektronix isn't able to provide support, and I am in need of a service
manual for this scope. Or advice on how to get the printer interface to
recognize the printer. The same printer and cable combination works on
several other Tektronix 2235 scopes, so I'm sure this one has a problem.

Thanks
Click to expand...


AFAIK the Tektronix 2235 (100 MHz, full analog, no diigtal storage; no
storage at all) was never manufactured with a printer nterface.

Maybe you are thinking of the 2230 or 2232: these ones use rs232
interfacing usually.

hth,
Andreas
 
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