I need help with fixing a Tektronix 2245A oscilloscope (long)
 

Hello all,

I bought this oscilloscope last weekend, it's the first one I've
owned. I have a basic understanding of electronics, my interest
mostly relates to keeping older stereo gear running, my own and the
stuff on permanant loan to family. So I usually am only opening
things up to change lamps and clean the pots. Anyway, I wanted to try
to gain a deeper understanding of how circuits work so I decided to
keep my eye out for a scope and now here I am.

The scope seemed to work fine with one exception: The intensity
control for 'A' (it has seperate controls for 'A' and 'B') seemed
wonky. When A was turned all the way down, there was still a trace
visible, which didn't seem right. As you turned it up it would stay
at the same intensity and then at about 40% it would suddenly get much
brighter.

I did a web search and found a couple of people who had issues with
the intensity control on the 22xx series of scopes (though none of
them had the same symptoms as mine), the problems ranged from a
defective/dirty pot, to a broken wire, to an open resistor, to a
problem IC (LM324). I also learned that this scope actually does a
POST when you turn it on and it will throw up an error message if
anything is majorly wrong. I also read the advice to keep a fan
blowing on it while the cover is off, which I have been doing.

I found a copy of the schematic (I have linked to excerpts here, the
whole service manual is 121 megs) and decided to do a cursory
examination; this also would give me a chance to see if the inside was
filthy which I was planning on checking at some point (actually, it
was very clean).

http://i.imgur.com/fu46CN4.jpg (intensity controls)

Well my problem wasn't a wire since the pot was soldered directly to
the CRT control board. I checked voltages at the 'A' control pot,
fine. R505 was nearby and was fine. It took a while to find LM324,
it was a mile away on the main board, half of it was poking out from
under a plastic cover that covered the high voltage section:

http://i.imgur.com/NnnRNvI.jpg (hv cover)

http://i.imgur.com/oCOyLOz.jpg (hv cover removed)

So I checked all the resistors in the above schematic associated with
'A' and they were all okay. However I did notice a resistor that was
burnt. Checking the board layout, it was R1027. It was at this point
I noticed the board layout in the service manual was different in
places than my actual unit.

http://i.imgur.com/abfYQAN.jpg (board layout)

This resistor is on this schematic:

http://i.imgur.com/AzCwCjt.jpg (power)

It's listed as a 0.2 W he

http://i.imgur.com/YYGMdZ0.jpg (parts list)

On paper it is supposed to be 10 ohms, it measured at 27. I check
R1026 to see if it matches the schematic and it is 10 ohms and it
looks fine (it's right next to the two 10uf caps in the picture). To
see what effect replacing this resistor would have, I put a couple of
resistors in parallel until I had 10 ohms total. The only effect
adding and taking away these resistors had was moving the trace
slightly up and down on the screen.

Now here's the thing - at some point during all this the intensity
problem seemed to fix itself. The trace would now go completely off
with the dial turned down all the way and it would get progressively
brighter as the control was turned. Okay, I was happy to leave it
alone except that I figured I should replace the resistor. I assumed
it got too hot being under that shroud. I took out the old resistor
(which flaked apart) and cleaned the area - the trace at one end was
blackened. I don't think I'm the one that caused this but I'm not
sure. The old resistor was too burnt to tell if it was original, it
was the same size as the others though.

Okay, now here's the actual problem - I replaced the resistor with a
0.5W one for good measure (the blue one just to the right of the
LM324):

http://i.imgur.com/oCOyLOz.jpg (hv cover removed)

I turn the unit on and it doesn't complain. The controls are still
working fine. I check the new resistor and it's very hot. Measure
the voltage across it: 4.6v. If my math is correct, that's 2 watts.
Turn it back off and let it cool. Back on to check voltages:
Incoming voltage to new resistor is +7.4v to ground. LM324 pin 4 to
ground is 2.7v. Voltage pin 4 to pin 11 (across IC) is 10 volts.
Voltage pin 11 to ground is -7.43 volts. Voltage after R1026 is -7.46
to ground. I desolder one end of R1026 and verify it is 10 ohms.
C1006 (the yellow guy near pin 7 of the IC) measures 47 ohms with a
multimeter. Shouldn't it read open? For reference, C1005 measures
about 100 ohms.

I'd just like to have an idea of what the problem might be before I
change any more components. Now I'm half wondering if it's the IC and
the fact that it's facing up and has a fan on it is allowing it to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html



















--- news://freenews.netfront.net/ - complaints: ---

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

On 07/24/2014 08:14 PM, Chris B. wrote:

about 100 ohms.

I'd just like to have an idea of what the problem might be before I
change any more components. Now I'm half wondering if it's the IC and
the fact that it's facing up and has a fan on it is allowing it to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

The problem is you bought the scope without the manual that should
accompany it as it travels through life. I lucked out and got my $225
465 from a Tek sales rep/ham. The 2" thick manual includes all repairs,
upgrades, part substitutions, liner notes, etc. In a perfect world the
manual travels with the device.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

dave prodded the keyboard

On 07/24/2014 08:14 PM, Chris B. wrote:

about 100 ohms.

I'd just like to have an idea of what the problem might be before I
change any more components. Now I'm half wondering if it's the IC
and the fact that it's facing up and has a fan on it is allowing it
to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

The problem is you bought the scope without the manual that should
accompany it as it travels through life. I lucked out and got my
$225 465 from a Tek sales rep/ham. The 2" thick manual includes all
repairs, upgrades, part substitutions, liner notes, etc. In a
perfect world the manual travels with the device.

Yes thats true ! I still have my Tek scope manual somewhere kicking
around... Unfortunately the scope got pinched.

--
Best Regards:
Baron.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

On Sun, 27 Jul 2014, dave wrote:

On 07/24/2014 08:14 PM, Chris B. wrote:

about 100 ohms.

I'd just like to have an idea of what the problem might be before I
change any more components. Now I'm half wondering if it's the IC and
the fact that it's facing up and has a fan on it is allowing it to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

The problem is you bought the scope without the manual that should accompany
it as it travels through life. I lucked out and got my $225 465 from a Tek
sales rep/ham. The 2" thick manual includes all repairs, upgrades, part
substitutions, liner notes, etc. In a perfect world the manual travels with
the device.

Wasn't there a place to hold the manual in many of the scopes? I can't
remember, but when I got my 545 (with some plug-ins) I seem to recall the
manual was in some slot or place in the case. Certainly the hospital
discards came with manuals. I was lucky, someone I knew grabbed it
all before it was tossed out

Michael

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

"Chris B." wrote:

Hello all,

I bought this oscilloscope last weekend, it's the first one I've
owned. I have a basic understanding of electronics, my interest
mostly relates to keeping older stereo gear running, my own and the
stuff on permanant loan to family. So I usually am only opening
things up to change lamps and clean the pots. Anyway, I wanted to try
to gain a deeper understanding of how circuits work so I decided to
keep my eye out for a scope and now here I am.

The scope seemed to work fine with one exception: The intensity
control for 'A' (it has seperate controls for 'A' and 'B') seemed
wonky. When A was turned all the way down, there was still a trace
visible, which didn't seem right. As you turned it up it would stay
at the same intensity and then at about 40% it would suddenly get much
brighter.

I did a web search and found a couple of people who had issues with
the intensity control on the 22xx series of scopes (though none of
them had the same symptoms as mine), the problems ranged from a
defective/dirty pot, to a broken wire, to an open resistor, to a
problem IC (LM324). I also learned that this scope actually does a
POST when you turn it on and it will throw up an error message if
anything is majorly wrong. I also read the advice to keep a fan
blowing on it while the cover is off, which I have been doing.

I found a copy of the schematic (I have linked to excerpts here, the
whole service manual is 121 megs) and decided to do a cursory
examination; this also would give me a chance to see if the inside was
filthy which I was planning on checking at some point (actually, it
was very clean).

http://i.imgur.com/fu46CN4.jpg (intensity controls)

Well my problem wasn't a wire since the pot was soldered directly to
the CRT control board. I checked voltages at the 'A' control pot,
fine. R505 was nearby and was fine. It took a while to find LM324,
it was a mile away on the main board, half of it was poking out from
under a plastic cover that covered the high voltage section:

http://i.imgur.com/NnnRNvI.jpg (hv cover)

http://i.imgur.com/oCOyLOz.jpg (hv cover removed)

So I checked all the resistors in the above schematic associated with
'A' and they were all okay. However I did notice a resistor that was
burnt. Checking the board layout, it was R1027. It was at this point
I noticed the board layout in the service manual was different in
places than my actual unit.

http://i.imgur.com/abfYQAN.jpg (board layout)

This resistor is on this schematic:

http://i.imgur.com/AzCwCjt.jpg (power)

It's listed as a 0.2 W he

http://i.imgur.com/YYGMdZ0.jpg (parts list)

On paper it is supposed to be 10 ohms, it measured at 27. I check
R1026 to see if it matches the schematic and it is 10 ohms and it
looks fine (it's right next to the two 10uf caps in the picture). To
see what effect replacing this resistor would have, I put a couple of
resistors in parallel until I had 10 ohms total. The only effect
adding and taking away these resistors had was moving the trace
slightly up and down on the screen.

Now here's the thing - at some point during all this the intensity
problem seemed to fix itself. The trace would now go completely off
with the dial turned down all the way and it would get progressively
brighter as the control was turned. Okay, I was happy to leave it
alone except that I figured I should replace the resistor. I assumed
it got too hot being under that shroud. I took out the old resistor
(which flaked apart) and cleaned the area - the trace at one end was
blackened. I don't think I'm the one that caused this but I'm not
sure. The old resistor was too burnt to tell if it was original, it
was the same size as the others though.

Okay, now here's the actual problem - I replaced the resistor with a
0.5W one for good measure (the blue one just to the right of the
LM324):

http://i.imgur.com/oCOyLOz.jpg (hv cover removed)

I turn the unit on and it doesn't complain. The controls are still
working fine. I check the new resistor and it's very hot. Measure
the voltage across it: 4.6v. If my math is correct, that's 2 watts.
Turn it back off and let it cool. Back on to check voltages:
Incoming voltage to new resistor is +7.4v to ground. LM324 pin 4 to
ground is 2.7v. Voltage pin 4 to pin 11 (across IC) is 10 volts.
Voltage pin 11 to ground is -7.43 volts. Voltage after R1026 is -7.46
to ground. I desolder one end of R1026 and verify it is 10 ohms.
C1006 (the yellow guy near pin 7 of the IC) measures 47 ohms with a
multimeter. Shouldn't it read open? For reference, C1005 measures
about 100 ohms.

I'd just like to have an idea of what the problem might be before I
change any more components. Now I'm half wondering if it's the IC and
the fact that it's facing up and has a fan on it is allowing it to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

A couple other sources:

http://www.ko4bb.com/manuals/index.p...tronix_-_2245A
http://w140.com/tekwiki/wiki/2245


This is the Tekscope group on Yahoo where people who collect and
repair Tek scopes can be found:


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

Michael Black wrote:

On Sun, 27 Jul 2014, dave wrote:

On 07/24/2014 08:14 PM, Chris B. wrote:

about 100 ohms.

I'd just like to have an idea of what the problem might be before I
change any more components. Now I'm half wondering if it's the IC and
the fact that it's facing up and has a fan on it is allowing it to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

The problem is you bought the scope without the manual that should accompany
it as it travels through life. I lucked out and got my $225 465 from a Tek
sales rep/ham. The 2" thick manual includes all repairs, upgrades, part
substitutions, liner notes, etc. In a perfect world the manual travels with
the device.

Wasn't there a place to hold the manual in many of the scopes? I can't
remember, but when I got my 545 (with some plug-ins) I seem to recall the
manual was in some slot or place in the case. Certainly the hospital
discards came with manuals. I was lucky, someone I knew grabbed it
all before it was tossed out


There was a removable vinyl pouch that screws to the top of that
family of scopes. Most get removed so you can stack other equipment on
top.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

dave wrote:

On 07/24/2014 08:14 PM, Chris B. wrote:

about 100 ohms.

I'd just like to have an idea of what the problem might be before I
change any more components. Now I'm half wondering if it's the IC and
the fact that it's facing up and has a fan on it is allowing it to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

The problem is you bought the scope without the manual that should
accompany it as it travels through life. I lucked out and got my $225
465 from a Tek sales rep/ham. The 2" thick manual includes all repairs,
upgrades, part substitutions, liner notes, etc. In a perfect world the
manual travels with the device.


In the real world, it is a pain in the ass to carry yet another item
you don't need. Just about any manual for a Tek scope is available in
..pdf format. Burn them to a disk or a USB stick and carry them that
way.

I have almost a dozen Tek scopes, and only have about a half dozen
paper manuals. I can print out the pages I need from a PDF, and if it's
searchable I can export the parts list into a text file to make notes on
without worrying about messing up a paper manual.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

Michael Black prodded the keyboard

On Sun, 27 Jul 2014, dave wrote:

On 07/24/2014 08:14 PM, Chris B. wrote:

about 100 ohms.

I'd just like to have an idea of what the problem might be before
I
change any more components. Now I'm half wondering if it's the IC
and the fact that it's facing up and has a fan on it is allowing
it to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

The problem is you bought the scope without the manual that should
accompany it as it travels through life. I lucked out and got my
$225 465 from a Tek sales rep/ham. The 2" thick manual includes all
repairs, upgrades, part substitutions, liner notes, etc. In a
perfect world the manual travels with the device.

Wasn't there a place to hold the manual in many of the scopes? I
can't remember, but when I got my 545 (with some plug-ins) I seem to
recall the
manual was in some slot or place in the case. Certainly the
hospital
discards came with manuals. I was lucky, someone I knew grabbed it
all before it was tossed out

Michael

Mr Terrell beat me to it :-)
Yes the scope had a pouch that fastened to the top. In my case it was
removed so that it would fit into the soft carry bag. I used to keep
the mains lead under the plastic front panel cover along with the
pair of scope probes.



--
Best Regards:
Baron.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

On Sun, 27 Jul 2014 07:02:57 -0700, dave
wrote:

On 07/24/2014 08:14 PM, Chris B. wrote:

about 100 ohms.

I'd just like to have an idea of what the problem might be before I
change any more components. Now I'm half wondering if it's the IC and
the fact that it's facing up and has a fan on it is allowing it to
work properly. Anyway, thanks for reading my long story and I'd
appreciate any suggestions you have.

This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

The problem is you bought the scope without the manual that should
accompany it as it travels through life. I lucked out and got my $225
465 from a Tek sales rep/ham. The 2" thick manual includes all repairs,
upgrades, part substitutions, liner notes, etc. In a perfect world the
manual travels with the device.

I agree it's annoying when someone doesn't take proper care of
something like this, but who knows how many times it's changed hands.
Actually, it's very clean inside but the CRT shield is a little
scratched; in addition to the pouch and the manual, these things also
originally came with a plastic front cover to prevent this.


--- news://freenews.netfront.net/ - complaints: ---

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

On Sun, 27 Jul 2014 17:48:20 -0400, "Michael A. Terrell"
wrote:


This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

A couple other sources:

http://www.ko4bb.com/manuals/index.p...tronix_-_2245A
http://w140.com/tekwiki/wiki/2245

The operators manual! Thank you very much, I couldn't find this
anywhere and I really do need it. The service manual seems to be the
same scan as the electrotanya one. From looking at the specs PDF, it
seems that the pouch and front cover was a $60 option - that explains
why so many that are being sold used are lacking them.

This is the Tekscope group on Yahoo where people who collect and
repair Tek scopes can be found:



Thanks, I'm not a big fan of private groups. Imagine all the
knowledge that will be lost when yahoo suddenly decides to scrap them.

--- news://freenews.netfront.net/ - complaints: ---

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

"Chris B." wrote in message
...
On Sun, 27 Jul 2014 17:48:20 -0400, "Michael A. Terrell"
wrote:


This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

A couple other sources:

http://www.ko4bb.com/manuals/index.p...tronix_-_2245A
http://w140.com/tekwiki/wiki/2245

The operators manual! Thank you very much, I couldn't find this
anywhere and I really do need it. The service manual seems to be the
same scan as the electrotanya one. From looking at the specs PDF, it
seems that the pouch and front cover was a $60 option - that explains
why so many that are being sold used are lacking them.

This is the Tekscope group on Yahoo where people who collect and
repair Tek scopes can be found:



Thanks, I'm not a big fan of private groups. Imagine all the
knowledge that will be lost when yahoo suddenly decides to scrap them.

--- news://freenews.netfront.net/ - complaints: ---

There are people on that group that have farmed all the message history just
for that reason. Neo was kind of a wakeup call.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

"Chris B." wrote:

On Sun, 27 Jul 2014 17:48:20 -0400, "Michael A. Terrell"
wrote:


This is where I downloaded the service manual:

http://elektrotanya.com/tektronix_22.../download.html

A couple other sources:

http://www.ko4bb.com/manuals/index.p...tronix_-_2245A
http://w140.com/tekwiki/wiki/2245

The operators manual! Thank you very much, I couldn't find this
anywhere and I really do need it. The service manual seems to be the
same scan as the electrotanya one. From looking at the specs PDF, it
seems that the pouch and front cover was a $60 option - that explains
why so many that are being sold used are lacking them.

This is the Tekscope group on Yahoo where people who collect and
repair Tek scopes can be found:



Thanks, I'm not a big fan of private groups. Imagine all the
knowledge that will be lost when yahoo suddenly decides to scrap them.


I have a zip of everything up to a few months ago. One of the
moderators created it, and a number of the group downloaded it. I have
every message posted after that, sorted by model number or subject for
non model specific items

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

On 07/27/2014 02:54 PM, Michael A. Terrell wrote:


way.

I have almost a dozen Tek scopes, and only have about a half dozen
paper manuals. I can print out the pages I need from a PDF, and if it's
searchable I can export the parts list into a text file to make notes on
without worrying about messing up a paper manual.


I am trying my best to live without printing anything. Why do you need
so many scopes? Do you sell them?

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

"Thanks, I'm not a big fan of private groups. Imagine all the
knowledge that will be lost when yahoo suddenly decides to scrap them. "

That is why we are on Usenet. Kinda like P2P when it came. Cannot kill it.

I need help with fixing a Tektronix 2245A oscilloscope (long)
 

dave wrote:

On 07/27/2014 02:54 PM, Michael A. Terrell wrote:


way.

I have almost a dozen Tek scopes, and only have about a half dozen
paper manuals. I can print out the pages I need from a PDF, and if it's
searchable I can export the parts list into a text file to make notes on
without worrying about messing up a paper manual.


I am trying my best to live without printing anything. Why do you need
so many scopes? Do you sell them?


I use some, others are collectibles like the Tek 323 and 324 that I
am restoring. I have two of each. Some are for NTSC video work. I have
two 2465 and one 2465A. The one I've had the longest is a 453A. I like
good analog scopes. :)


http://w140.com/tekwiki/wiki/Main_Page is a nice resource for people who
use or collect older Tek scopes.


I have somewhere around a thousand printed service manuals. Most were
made before PDF was common.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.