Date   
Re: 2445A calibration

Siggi
 

On Mon, 15 Oct 2018 at 15:41 <maxim.vlasov@...> wrote:

Looks like slowly but surely I make some progress. Just found that U2420D
buffer is sinking 11mA. I measure at the U2420D output -8.8V but TP2421 is
-1.25V. 11mA flowing through R2220 (680 Ohm). I've looked at the schematics
and 11mA doesn't seem to be the current to be pulled out of TP2421. There
are quite a bit of loads, but all of them in a range of dozens of KOhms.
Something is pulling up -1.25V rail.
I don't know whether that's unreasonable, but -8.8V out of the op-amp is
well within its control range. A TL074 will go to +12/-12V minimum on a
+15/-15V supply so I wouldn't focus there too much. If you look at the
power distribution diagram <11>(?), you'll see U700/U850/U900 get -1.25V
bias, so 11mA is probably reasonable.


Have you observed this on your scopes when repairing?
Sadly I haven't measured this - if you're stuck, I can pop the case on my
2467 this weekend and check it. Offhand, I don't think 11mA is unreasonable
however.


One more thing - I've got -04 FW version. It seems like the last version
was -09 for 2467 o-scope. I wonder whether I can run the latest FW. If so,
then in the guts of the o-scope there should be a HW identification
register somewhere to tell to the FW whether it's 2445/55/65 or 67, IMHO.
Otherwise the code is almost the same.
I updated my firmware from -06 to -09 without incident. Didn't need
re-calibration that I noticed.

Re: Tek 2467B

Robert Calk Jr.
 

Hi guys,

Here are some photos. I hope that this works!

https://groups.io/g/TekScopes/album?id=75892

Robert

Re: 2445A calibration

maxim.vlasov@...
 

Siggi, Chuck, thank you for your answers,

I'll upgrade the firmware to -09. Also, hope that the calibration procedure will be more forgiving (maybe)....

Also will see what is consuming 11mA. After checking the TL072/082 and LF347N datasheets, found in LF347N the maximum voltage swing vs sink/source current rating, which is -/+12V under -/+10mA. So the operating range is close to its limit but not marginal yet.
Have to check C731 220uF capacitor on A1.
Well, I've made a small LTSpice simulation (see the schematics below) to check the DC operating point and find the currents and voltages:
https://groups.io/g/TekScopes/photo/74577/0?p=Name,,,20,1,0,0

It's very unfortunate, but it seems like everything is well in spec, so I've changed the U2420 for no reason.. Siggi, thanks a lot for offering the help in opening your scope, but it looks like everything is nominal and designed to be like this (arghhh)...
-1.25V reference and +1.36 runs through A1 and also the front board. All the pots are connected to these two rails. This circuit also includes the hold-off, SWEEP A/B ICs and even the attenuator temperature controls (every single thing measured back by ADC runs off the DAC 1mA REF. Logical, but scattered and fragile).

What I found really weird on the running oscilloscope is the difference between the A5 ground and A1 ground potential is about 0.3mV. 300uV! Also same gradient found on A5, going from 0 to about 0.3mV as measuring between ground traces on the board.

If someone have connected the o-scope to HV or the life AC and got the frontend busted, I could only assume that the ground could get compromised on A1 (somewhere between the BNC probe ground and the AC plug ground).

When you have repaired the o-scopes have you found a weak point of some sort, which can be damaged by the excessive current between BNC and the power socket GND?

Thank you,

Re: 2445A calibration

Chuck Harris
 

The BNC goes directly to chassis ground, so, your answer
is no. There is no weak point between the BNC and the
power line bond wire. Working on telephone station equipment,
I occasionally got caught by the grounding conventions, and
once burned up a probe ground wire on a 2465 without issue.

Have you solved the problem of your cursor vs the 1st and
11th graticule line yet? If not, you are still playing in
the wrong ball park. You cannot pass CAL01 and CAL02 if you
cannot get the cursor and the graticule to match each other.

The cursor is how the calibration routines know how wide the
spacing between the graticule lines is.

Also, it sounds a little to me like you don't understand that
Tek used the opamp as the "pass transistor" for the -1.25 and
+1.36 reference power supplies.

-Chuck Harris

maxim.vlasov@... wrote:

Siggi, Chuck, thank you for your answers,

I'll upgrade the firmware to -09. Also, hope that the calibration procedure will be more forgiving (maybe)....

Also will see what is consuming 11mA. After checking the TL072/082 and LF347N datasheets, found in LF347N the maximum voltage swing vs sink/source current rating, which is -/+12V under -/+10mA. So the operating range is close to its limit but not marginal yet.
Have to check C731 220uF capacitor on A1.
Well, I've made a small LTSpice simulation (see the schematics below) to check the DC operating point and find the currents and voltages:
https://groups.io/g/TekScopes/photo/74577/0?p=Name,,,20,1,0,0

It's very unfortunate, but it seems like everything is well in spec, so I've changed the U2420 for no reason.. Siggi, thanks a lot for offering the help in opening your scope, but it looks like everything is nominal and designed to be like this (arghhh)...
-1.25V reference and +1.36 runs through A1 and also the front board. All the pots are connected to these two rails. This circuit also includes the hold-off, SWEEP A/B ICs and even the attenuator temperature controls (every single thing measured back by ADC runs off the DAC 1mA REF. Logical, but scattered and fragile).

What I found really weird on the running oscilloscope is the difference between the A5 ground and A1 ground potential is about 0.3mV. 300uV! Also same gradient found on A5, going from 0 to about 0.3mV as measuring between ground traces on the board.

If someone have connected the o-scope to HV or the life AC and got the frontend busted, I could only assume that the ground could get compromised on A1 (somewhere between the BNC probe ground and the AC plug ground).

When you have repaired the o-scopes have you found a weak point of some sort, which can be damaged by the excessive current between BNC and the power socket GND?

Thank you,

Re: 7834 High Voltage Board

ef804s tubes
 

Hi Craig,
that's correct.

Fred

I still have one Mesh Filter for a 475 Scope left.

 

I found one more 4 5/8" (11.7475cm) x 3 7/8" (9.8425cm) mesh filters for the
475 to reduce glare and improve the contrast of your CRT.

There is no charge for the mesh.

The only charge is $15.00 to cover the postage, packaging, and transport to
the post office.



If you can use it please contact me directly off list at dennis at ridesoft
dot com and include your address.



Dennis Tillman W7PF



Thanks to:

Fred Schumacher for explaining what they are used for and which scope they
fit.

Lop Pol for confirming they are not for the 453 or 454

Renée for suggesting which scope they are for

Re: 2445A calibration

maxim.vlasov@...
 

On Mon, Oct 15, 2018 at 09:29 PM, Chuck Harris wrote:


Also, it sounds a little to me like you don't understand that
Tek used the opamp as the "pass transistor" for the -1.25 and
+1.36 reference power supplies.
Thank you Chuck, but now I understand in every little detail how the reference is generated and distributed all across the o-scope including the programmatic values and the expected convergence DC point after finding the DAC code and running the smal simulation.

I had to give the thorough test and find the explanation to whatever was discovered. IMHO, the problem is related to the operation or the calibration of the ADC/DAC since it fails one of automated routines. Now since the hypothesis about the bad reference distribution is dead, then I'll go with the raster step. If the raster step is OK, then then I had to pass the 1st and 11th graticules after the DAC ref current calibration. Otherwise I'll have to go back to the multichannel DAC/ADC and continue checking the sample&hold caps, muxers and the rest.

I'm advancing slowly (have not more than 40 mins per day), so please be patient with me.

Thank you,

Maxim

Re: 7834 High Voltage Board

Mark Wendt
 

On 10/16/18 00:50, ef804s tubes wrote:
Hi Craig,
that's correct.

Fred

What's correct?  It helps us follow the conversation if you quote the passage you are replying to.  There are also multiple Craig's on the list, any of which may have replied before to this thread. I've quoted your message for example.  Now folks know who I'm replying to, and why I'm replying.  Now there is context to my reply.


Mark

Re: 7834 High Voltage Board

Colin Herbert
 

While I agree that quoting text does make stuff a lot clearer, doesn't the message title help with following the conversation, too? I am a sad person who doesn't delete any of these messages from Tekscopes - I find it easier to follow the context that way.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mark Wendt
Sent: 16 October 2018 13:41
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7834 High Voltage Board

On 10/16/18 00:50, ef804s tubes wrote:
Hi Craig,
that's correct.

Fred

What's correct? It helps us follow the conversation if you quote the
passage you are replying to. There are also multiple Craig's on the
list, any of which may have replied before to this thread. I've quoted
your message for example. Now folks know who I'm replying to, and why
I'm replying. Now there is context to my reply.


Mark

Re: 7834 High Voltage Board

Mark Wendt
 

I tend to keep messages that actually help me down the road with troubleshooting something, or may possibly just touch my interest at that moment.  I've been sending and receiving email for over thirty years.  If I'd kept every single email I'd received over those years, I'd never be able to sort through it and find something that I needed.  A "that's correct" reply with no context isn't worth the few bits that entail the email to not delete.

Mark

On 10/16/18 08:45, Colin Herbert via Groups.Io wrote:
While I agree that quoting text does make stuff a lot clearer, doesn't the message title help with following the conversation, too? I am a sad person who doesn't delete any of these messages from Tekscopes - I find it easier to follow the context that way.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mark Wendt
Sent: 16 October 2018 13:41
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7834 High Voltage Board

On 10/16/18 00:50, ef804s tubes wrote:
Hi Craig,
that's correct.

Fred

Re: 7834 High Voltage Board

ArtekManuals
 

NOT REALLY IN MANY CASES

On 10/16/2018 8:45 AM, Colin Herbert via Groups.Io wrote:
While I agree that quoting text does make stuff a lot clearer, doesn't the message title help with following the conversation, too? I am a sad person who doesn't delete any of these messages from Tekscopes - I find it easier to follow the context that way.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mark Wendt
Sent: 16 October 2018 13:41
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7834 High Voltage Board

On 10/16/18 00:50, ef804s tubes wrote:
Hi Craig,
that's correct.

Fred
What's correct? It helps us follow the conversation if you quote the
passage you are replying to. There are also multiple Craig's on the
list, any of which may have replied before to this thread. I've quoted
your message for example. Now folks know who I'm replying to, and why
I'm replying. Now there is context to my reply.


Mark







--
Dave
Manuals@...
www.ArtekManuals.com

Quoting prior messages (Re: [TekScopes] 7834 High Voltage Board)

ArtekManuals
 

I am with Mark on this.. Generally when I see a message with out the necessary background in it I just delete it without reading, other wise I have to log on to IO and find the history on the thread ...life is too short. The only thing worse is hijacking threads with out changing the subject line
Dave
manuals@...

On 10/16/2018 8:40 AM, Mark Wendt wrote:
On 10/16/18 00:50, ef804s tubes wrote:
Hi Craig,
that's correct.

Fred

What's correct?  It helps us follow the conversation if you quote the passage you are replying to.  There are also multiple Craig's on the list, any of which may have replied before to this thread. I've quoted your message for example.  Now folks know who I'm replying to, and why I'm replying.  Now there is context to my reply.


Mark



--
Dave
Manuals@...
www.ArtekManuals.com

Re: 2445A calibration

Chuck Harris
 

Hi Maxim,

I applaud your efforts, but I wonder if they aren't being
wasted... wasted, assuming your goal is to calibrate your
scope...

40 minutes isn't a lot of time to use I hate to see you spend
it chasing normal production variations.

I think your scope is working properly, but you have botched
a couple of calibration steps that are most crucial.

You have already adjusted the DAC into its 2.5V range, and
it seems to me to be typically distributed.

The next automatic steps follow the first few steps of CAL01
and CAL02. Those first steps are where your eyes help the
calibration routine figure out how the cursor's position,
and the DAC's steps relate to the CRT's graticule positions.

That relationship is used throughout the rest of the scope's
calibration.

You can see how well you have done when the scope does its
spot dance in steps 111 and 112... and in the other little
automatic sections. The beam does a successive approximation
sequence where it starts some distance away from the graticule,
and converges onto the graticule intersections.

If you haven't properly related the graticule to the cursor,
it will miss the graticule intersection.

-Chuck Harris

maxim.vlasov@... wrote:

On Mon, Oct 15, 2018 at 09:29 PM, Chuck Harris wrote:


Also, it sounds a little to me like you don't understand that
Tek used the opamp as the "pass transistor" for the -1.25 and
+1.36 reference power supplies.
Thank you Chuck, but now I understand in every little detail how the reference is generated and distributed all across the o-scope including the programmatic values and the expected convergence DC point after finding the DAC code and running the smal simulation.

I had to give the thorough test and find the explanation to whatever was discovered. IMHO, the problem is related to the operation or the calibration of the ADC/DAC since it fails one of automated routines. Now since the hypothesis about the bad reference distribution is dead, then I'll go with the raster step. If the raster step is OK, then then I had to pass the 1st and 11th graticules after the DAC ref current calibration. Otherwise I'll have to go back to the multichannel DAC/ADC and continue checking the sample&hold caps, muxers and the rest.

I'm advancing slowly (have not more than 40 mins per day), so please be patient with me.

Thank you,

Maxim



Re: Quoting prior messages (Re: [TekScopes] 7834 High Voltage Board)

Sergey Kubushyn
 

On Tue, 16 Oct 2018, Artekmedia wrote:

+1 for me. All those "Me too" (pun intended) messages are absolutely
worthless, waste precious electrons, and just ignorant.

People, please learn some netiquette. Do _NOT_ post "Correct", "Yes", "Me
too" and following messages without including original text. NEVER EVER.

Remember, there are people there who use TEXT mail readers (i.e. this
message has been written in alpine) and VERY rarely log in to groups.io (or
whatever) to use that stupid shiny-blinky GUI tool. We do NOT have time to
browse all those forums and their ilk -- whatever we receive is a part of
regular mail stream that ends up in our mail boxes along with tons of other
stuff. We do go through our boxes once in a while doing actual job all other
time.

There is also another thing -- all those shiny-blinky forums with their
messages are hosted by _SOMEBODY_ and when (not "if" -- it is ALWAYS "when")
that somebody goes belly-up all data is lost. In case of well quoted email
thread everything is saved on your local machine so whatever happened to a
hoster you still have all the info.

I am with Mark on this.. Generally when I see a message with out the necessary background in it I just delete it without reading, other wise I have to log on to IO and find the history on the thread ...life is too short. The only thing worse is hijacking threads with out changing the subject line
Dave
manuals@...

On 10/16/2018 8:40 AM, Mark Wendt wrote:
On 10/16/18 00:50, ef804s tubes wrote:
Hi Craig,
that's correct.

Fred
What's correct?  It helps us follow the conversation if you quote the
passage you are replying to.  There are also multiple Craig's on the list,
any of which may have replied before to this thread. I've quoted your
message for example.  Now folks know who I'm replying to, and why I'm
replying.  Now there is context to my reply.

Mark

--
Dave
Manuals@...
www.ArtekManuals.com
---
******************************************************************
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
******************************************************************

Re: 7834 High Voltage Board

ef804s tubes
 

On Mon, Oct 15, 2018 at 09:09 AM, Craig Sawyers wrote:


What you seem to be saying is that the main power supply works fine when the
coax inputs to T2010 are
not connected, but when you connect them the main supply goes into tick mode?

Is that correct?

Craig
Hi Craig,
that's correct.

Fred

My apologies for not quoting the question

Re: 7834 High Voltage Board

Mark Wendt
 

On 10/16/18 10:55, ef804s tubes wrote:
On Mon, Oct 15, 2018 at 09:09 AM, Craig Sawyers wrote:

What you seem to be saying is that the main power supply works fine when the
coax inputs to T2010 are
not connected, but when you connect them the main supply goes into tick mode?

Is that correct?

Craig
Hi Craig,
that's correct.

Fred

My apologies for not quoting the question

Thanks!  That helps those of us who use an email client keep track of the conversation, what question is being asked, who asked it and how you responded to it.  We tend to get some pretty involved conversations going, which can have hundreds of responses to help, ask questions, and give answers.  We have a bunch of Dave's, some Craig's and a few other folks with the same names. It helps us keep track of which question you are responding to, and watching as the troubleshooting unfolds.


Mark

Re: 2445A calibration

Max Vlasov
 

On Tue, Oct 16, 2018 at 06:26 AM, Chuck Harris wrote:


If you haven't properly related the graticule to the cursor,
it will miss the graticule intersection.
Hello, Chuck,

Thank you for this point. I'll work on it tonight.

Just one more clarification.
Over the lunch I've read PG506 user's manual again and one thing became apparent:
http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Tektronix%20PG506%20Calibration%20Generator.pdf
The table 4-5 page 35 in the PG506 UM states the voltage readings vs the generator amplitude settings when the "standard output" of PG506 is loaded by 50 Ohm.

So, basically since the output voltage setting is done on PG506 selector regardless its output load, loading the PG506 with 50Ohm load will halve the output amplitude on the standard output.

Also in 2445a service manual they say:
"Connect a 0.5V standard-amplitude signal from Calibration Generator to the CH1 or X input connector via 50 Ohm BNC cable"
After all, what are the settings to be set on PG506? 0.5V or 1.0V? 0.5V set on PG506 will result in 250mV signal on CH1/2 of o-scope (instead of 500mV signal applied from AWG).

I'm suspecting the double voltage settings on AWG here and why:
Table 5-4 "Vertical Calibration Signals" in the 2445a SM states that during the autocalibration steps 113 to 120 the "Standard Amplitude Signal" to be applied will range from 20mV to 10V. We remember this 10V! This 10V in 50 Ohm? or 10V set on PG506 producing 5V into 50Ohm load?
Now, if we go back to PG506 user's manual table 4-5 which is used for the 50Ohm load performance testing, we see that when the output is 50Ohm terminated the PG506 for the 10V setting the generator produces 5V, but this is the last entry in the table. There is no 20V setting under 50 Ohm load to produce 10V. The PG506 standard output can't cope with 50Ohm load when set to 20V!

I wonder whether this is a MEGA GOTCHA?

Summary: PG506 is not designed to provide more than 5V peak-peak from its "standard output" to 50Ohm load. I.e. in my case when asked by the CAL routing to set 10V I have to set 5V, IMHO, but I did it wrong and this caused the LIMIT error.

This also explains why I had no LIMIT error when by the mistake on the cal steps 120&130 I didn't set the 10V level (physically 10Vp-p to 50Ohmon the AWG output) but instead I've left it at 5Vp-p to 50Ohm. All the other times I always had the LIMIT error on every single step.

If true then I was screwing up the fully working oscilloscope....


Could you, please, confirm or deny the above?

Thank you,

Maxim

Re: 2445A calibration

Siggi
 

On Tue, 16 Oct 2018 at 11:31 Max Vlasov via Groups.Io <maxismsx=
yahoo.com@groups.io> wrote:

The PG506 standard output can't cope with 50Ohm load when set to 20V!
Um, that's backwards. Your scope's 50 Ohm terminator is specified to
tolerate 5V RMS max. That's 0.5W.
At 20V RMS, you'd be pumping 8W into it, which'd be sure to blow it if the
overtemp protection is disabled. Sufficient overload will blow the
terminator regardless, as the protection has a finite reaction time.

Re: 2445A calibration

Max Vlasov
 

On Tue, Oct 16, 2018 at 08:56 AM, Siggi wrote:


Um, that's backwards. Your scope's 50 Ohm terminator is specified to
tolerate 5V RMS max. That's 0.5W.
At 20V RMS, you'd be pumping 8W into it, which'd be sure to blow it if the
overtemp protection is disabled.
Siggi,
this is exactly the point. The vertical calibration procedure tells you to set certain levels (normally from 0V to the requested level, we have already discussed this above), but effectively it seems like it's necessary to divide all the requested levels by 2 (which I haven't done, set the requested level on the AWG and got the LIMIT error). If the hypothesis is right, then I've de-tuned already whatever is possible to detune ;) I haven't touched the DAC BTW, yet ;) Just a few opamps around...

That's why I'm asking Chuck this question since he's got the calibrator under the hand. I don't have the calibration for the vertical setup...

Thank you !

Re: 2445A calibration

Chuck Harris
 

Hi Maxim,

I misspoke earlier, the PG506 is exactly 50 ohms output
impedance in the standard amplitude output position.

That is to say, its Norton Equivalent is an ideal voltage
generator, with a 50 ohm series resistor.

It will output the knob voltage when terminated with 1M,
and 1/2 the knob voltage when terminated with 50 ohms.

It is always used with 1M termination when doing the
voltage calibration of a 2465B.

More to the point, I suppose, the 2465B's calibration
routine automatically selects the proper input impedance
for any step of the automated test.

*you do not add any loads the test doesn't ask for*

If it asks for 1Vp-p, you give it 1Vp-p as shown on the
PG506's knob, and probably 1/2Vp-p as shown on your AWG's
knob.

-Chuck Harris


Max Vlasov via Groups.Io wrote:

On Tue, Oct 16, 2018 at 06:26 AM, Chuck Harris wrote:


If you haven't properly related the graticule to the cursor,
it will miss the graticule intersection.
Hello, Chuck,

Thank you for this point. I'll work on it tonight.

Just one more clarification.
Over the lunch I've read PG506 user's manual again and one thing became apparent:
http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Tektronix%20PG506%20Calibration%20Generator.pdf
The table 4-5 page 35 in the PG506 UM states the voltage readings vs the generator amplitude settings when the "standard output" of PG506 is loaded by 50 Ohm.

So, basically since the output voltage setting is done on PG506 selector regardless its output load, loading the PG506 with 50Ohm load will halve the output amplitude on the standard output.

Also in 2445a service manual they say:
"Connect a 0.5V standard-amplitude signal from Calibration Generator to the CH1 or X input connector via 50 Ohm BNC cable"
After all, what are the settings to be set on PG506? 0.5V or 1.0V? 0.5V set on PG506 will result in 250mV signal on CH1/2 of o-scope (instead of 500mV signal applied from AWG).

I'm suspecting the double voltage settings on AWG here and why:
Table 5-4 "Vertical Calibration Signals" in the 2445a SM states that during the autocalibration steps 113 to 120 the "Standard Amplitude Signal" to be applied will range from 20mV to 10V. We remember this 10V! This 10V in 50 Ohm? or 10V set on PG506 producing 5V into 50Ohm load?
Now, if we go back to PG506 user's manual table 4-5 which is used for the 50Ohm load performance testing, we see that when the output is 50Ohm terminated the PG506 for the 10V setting the generator produces 5V, but this is the last entry in the table. There is no 20V setting under 50 Ohm load to produce 10V. The PG506 standard output can't cope with 50Ohm load when set to 20V!

I wonder whether this is a MEGA GOTCHA?

Summary: PG506 is not designed to provide more than 5V peak-peak from its "standard output" to 50Ohm load. I.e. in my case when asked by the CAL routing to set 10V I have to set 5V, IMHO, but I did it wrong and this caused the LIMIT error.

This also explains why I had no LIMIT error when by the mistake on the cal steps 120&130 I didn't set the 10V level (physically 10Vp-p to 50Ohmon the AWG output) but instead I've left it at 5Vp-p to 50Ohm. All the other times I always had the LIMIT error on every single step.

If true then I was screwing up the fully working oscilloscope....


Could you, please, confirm or deny the above?

Thank you,

Maxim