Date   

Re: TDS 620A vs. TDS 620B questions and repair inquiry

nonIonizing EMF
 

On Sun, Jun 9, 2019 at 07:25 AM, David Berlind wrote:


3. The 620B did not come with any probes when I purchased it. I noticed from
the 620A documentation that that scope originally came with a 6139A probe
which lead me into an exploration of probe characteristics. That probe's specs
appear to match the 500Mhz capability of the scope. Over the last two years, I
haven't thought much about the probes themselves. Just been using what I
acquired along the way and things seem to work. So, in the spirit of rooting
out any configuration problems before needing to effect any repairs, to what
extent could basic probe differences impact behavior? For example, I have some
basic 1X/10x probes (which might not be rated for 500Mhz) that work nicely on
my 7603. What incompatibilities could exist between these probes and the 620B
such that I might get unexpected/inaccurate behavior?
Here are some references for those not on the FB Old Tek Scopes group, might not have seen the latest post regarding Tek probes or haven't seen these references before ( https://www.facebook.com/groups/oldtekscopes/permalink/435036140617897/ ) :

http://www.barrytech.com/tektronix/probes/tekprobes.html


I'm thinking these are older probes references so might not be pertinent though may have some utility from the info in the links:

https://web.archive.org/web/20180307162334/http://www.reprise.com/host/tektronix/reference/default.asp (two links might provide some details)

http://w140.com/tek_probe_crossref_1990.pdf (more of an older scope reference)


I've not gotten around to verifying the "A", "B", "C" and "D" model codes... though seems from general reading there are TDS-5XX/6XX/7XX family associated capabilities detailed (I forget at the time being).


Re: TDS 620A vs. TDS 620B questions and repair inquiry

Siggi
 

On Sun, Jun 9, 2019 at 10:25 AM David Berlind <david@berlind.org> wrote:

1. I could not locate an online manual for the 620B. I found the Technical
Reference and printed that out. But in terms of the User Manual, I could
only find a manual for the 620A (could just be bad Googling skills). So, I
downloaded and printed that out. Now, I'm trying to ascertain whether the
620A manual is for the most part applicable (should have done this before
killing a tree to print it I guess) or whether the 620A is different enough
from the 620B that the manual doesn't apply.
I think a significant difference between the 600A and 600B generations is
that the Bs have peak detect acquisition mode. This allows them to catch
1ns (?) peaks even at slow sweep speeds.

Note that the TDS600-series scopes are CCD-based (like the 2430-2440s of
old), whereas the TDS500/700-series are ADC-based. The CCD scopes don't
slow down the acquisition rate as you turn on more channels, but they don't
have equivalent time nor hi-res sampling modes.
They also tend to have more limited record length, and I believe they have
more dead time than the 500/700s. This is due to the fact that while they
capture into the CCD at a very quick rate, the contents of the CCD are then
digitized at a pretty leisurely rate after a trigger is detected.


Re: TDS 620A vs. TDS 620B questions and repair inquiry

Siggi
 

On Sun, Jun 9, 2019 at 10:25 AM David Berlind <david@berlind.org> wrote:

Hi all,

After starting my oscilloscope journey with analog scopes for the last two
years and seeing some of what the digital scopes could do (for example,
maths), I had been watching my local marketplaces carefully for a good
price on a digital scope in working condition. I recently picked up at TDS
620B for $85 and am now beginning the journey of getting to know it. I will
be posting video of its behavior which I think may be in need of correction
based on initial observations.. and I am of course looking for advice. But
I may be wrong about that. I will work on eliminating other issues first
(configuration, line noise, etc.).

My first inquiry involves four questions:

1. I could not locate an online manual for the 620B. I found the Technical
Reference and printed that out. But in terms of the User Manual, I could
only find a manual for the 620A (could just be bad Googling skills). So, I
downloaded and printed that out. Now, I'm trying to ascertain whether the
620A manual is for the most part applicable (should have done this before
killing a tree to print it I guess) or whether the 620A is different enough
from the 620B that the manual doesn't apply. I've been looking for some way
to compare the two side by side (I found some differently formatted data
and specification sheets so apples to apples isn't perfect, but there's
some overlapping data to get some jist). But I thought it would be prudent
to toss the question out to this group because maybe someone will just know
and can summarize key differences and how that impacts anything (usage,
probes, etc).

2. I'll take any suggestions from you pros on great ways to get started
with this scope. Configurations to try. Shortcuts. Anything that will
fast-track my introduction to expert operation of the scope.

3. The 620B did not come with any probes when I purchased it. I noticed
from the 620A documentation that that scope originally came with a 6139A
probe which lead me into an exploration of probe characteristics. That
probe's specs appear to match the 500Mhz capability of the scope. Over the
last two years, I haven't thought much about the probes themselves. Just
been using what I acquired along the way and things seem to work. So, in
the spirit of rooting out any configuration problems before needing to
effect any repairs, to what extent could basic probe differences impact
behavior? For example, I have some basic 1X/10x probes (which might not be
rated for 500Mhz) that work nicely on my 7603. What incompatibilities could
exist between these probes and the 620B such that I might get
unexpected/inaccurate behavior?

4. Wondering whether it might be best and faster just to have the pros
take a look at the scope, I have inquired with a local calibration service
as to the cost of a "tune-up." The estimate just for calibration for was
over $300 (way more than the cost of the scope). It dawned on me that one
option might be to pay someone in this group to bring her up to snuff. This
is for hobbyist work (repairing amps, radios, etc) so it's not like I need
a certificate. Is there someone here who does that sort of thing?

Thank you.

David




Re: TDS 620A vs. TDS 620B questions and repair inquiry

Harvey White
 

Very rough rule of thumb on square waves.  A "decent" square wave requires response to about 10x the fundamental frequency.  (it only has odd harmonics).  So your 1 Khz calibrator requires a decent frequency response to (gasp!) 10 Khz.

Still, the frequency compensation on most adjustable probes is decent enough when done at 1 Khz.  For other frequencies and the like, the "flat top" of the square wave will likely be insufficient.  That also varies per probe.  The P6015 high voltage probe has at least six or seven separate adjustments for frequency response and flatness.

Normally, though, what Tek did is to optimize pulse response over flatness of frequency response.

Video looks good to me.

Harvey

On 6/9/2019 1:29 PM, David Berlind wrote:
As I await all your answers, I started with page 1 of the manual this morning and am liking the functionality. Compared to my initial quick-plug-it-in see if it works the other day, things went much better. The first thing I did was a factory reset (following the manual's instructions of course). This may have fixed a few things. Working with the probe calibration signal, here's a video of what I observed after selecting some measurements for display. I'm using some100Mhz probes at 1x.

https://photos.app.goo.gl/8Lt8pPpUCVgPPUw1A


On June 9, 2019 11:42:15 AM "Stephen Hanselman" <kc4sw.io@kc4sw.com> wrote:

I don’t have a lot of knowledge but two things. In the 540, 540A, 540C, etc the “ “ and “A” speak a different HPIB language from the “B” and “C”. If a lab says calibration for $300 they “may” hook it up and make sure the readings are close but not much else.

I don’t know what a fully automated set could do, I do all my calibrations manually with the Tek software.  The 540B takes about 5 hours to do a good job.  If you were close I say bring it by and turn you loose on my software.

Regards,

Stephen Hanselman
Datagate Systems, LLC
3107 North Deer Run Road #24
Carson City, Nevada, 89701
(775) 882-5117 office
(775) 720-6020 mobile
s.hanselman@datagatesystems.com
www.datagatesystems.com
a Service Disabled, Veteran Owned Small Business
DISCLAIMER:
This e-mail and any attachments are intended only for use by the addressee(s) named herein and may contain legally privileged and/or proprietary information. If you are not the intended recipient, any dissemination, distribution or copying of this e-mail and any attachments is strictly prohibited. If you have received this e-mail in error, please immediately notify me and permanently delete the original and all copies and printouts of this e-mail and any attachments.
On Jun 9, 2019, at 08:25, David Berlind <david@berlind.org> wrote:


Hi all,


After starting my oscilloscope journey with analog scopes for the last two years and seeing some of what the digital scopes could do (for example, maths), I had been watching my local marketplaces carefully for a good price on a digital scope in working condition. I recently picked up at TDS 620B for $85 and am now beginning the journey of getting to know it. I will be posting video of its behavior which I think may be in need of correction based on initial observations.. and I am of course looking for advice. But I may be wrong about that. I will work on eliminating other issues first (configuration, line noise, etc.).


My first inquiry involves four questions:


1. I could not locate an online manual for the 620B. I found the Technical Reference and printed that out. But in terms of the User Manual, I could only find a manual for the 620A (could just be bad Googling skills). So, I downloaded and printed that out. Now, I'm trying to ascertain whether the 620A manual is for the most part applicable (should have done this before killing a tree to print it I guess) or whether the 620A is different enough from the 620B that the manual doesn't apply. I've been looking for some way to compare the two side by side (I found some differently formatted data and specification sheets so apples to apples isn't perfect, but there's some overlapping data to get some jist). But I thought it would be prudent to toss the question out to this group because maybe someone will just know and can summarize key differences and how that impacts anything (usage, probes, etc).


2. I'll take any suggestions from you pros on great ways to get started with this scope. Configurations to try. Shortcuts. Anything that will fast-track my introduction to expert operation of the scope.


3. The 620B did not come with any probes when I purchased it. I noticed from the 620A documentation that that scope originally came with a 6139A probe which lead me into an exploration of probe characteristics. That probe's specs appear to match the 500Mhz capability of the scope.  Over the last two years, I haven't thought much about the probes themselves. Just been using what I acquired along the way and things seem to work. So, in the spirit of rooting out any configuration problems before needing to effect any repairs, to what extent could basic probe differences impact behavior? For example, I have some basic 1X/10x probes (which might not be rated for 500Mhz) that work nicely on my 7603. What incompatibilities could exist between these probes and the 620B such that I might get unexpected/inaccurate behavior?


4. Wondering whether it might be best and faster just to have the pros take a look at the scope, I have inquired with a local calibration service as to the cost of a "tune-up."  The estimate just for calibration for was over $300 (way more than the cost of the scope). It dawned on me that one option might be to pay someone in this group to bring her up to snuff. This is for hobbyist work (repairing amps, radios, etc) so it's not like I need a certificate. Is there someone here who does that sort of thing?


Thank you.


David






Re: PG506 ISSUES Need some experienced minds!

Albert Otten
 

Michael,

If you got a headache from the High Ampl diagram <5> you're in good comany. The way this diagram is drawn is terrible. We complained about this already many years ago. And you are lucky to have the B-04 up version since the earlier diagram also showed circuit modifications (and errors around VR792). For now I roughly redraw the diagram (once more) in my own way.
It's a pity that you only measured with Ampl set to MAX. The unloaded -63 V looks good, but could just as well be the end of the regulation range (with 14 V feedback to CR27) while actually there is no regulation. I hoped you would find an increasingly more negative "-72V" when you rotate Ampl further clockwise. A setting mid-way or so would be good to measure at more points in the circuits.
Anyway, -6 V when loaded is for sure not negative enough. (BTW "loaded" has not to be read in the sense that the output transistors have to deliver more power. The form a constant current supply (when on) to feed 600R || load.)
The gate of Q758 is at about a 9 V more positive voltage than "-72V" (VR792 + VR790 + CR734). The gate is always negative because current supplier Q790 has its base at ground.
When the output is on, the drain of Q758 is about 1.5 V more negative negative than the output voltage and the C800 voltage. That C800 voltage is compared with the gate voltage by U840. The voltage dividers to +5V, 100k to 4k53, are the same but R827 (to ground) and R840 (to pin 6) destroy the symmetry. U840 regulates the voltage difference between pin 2 and pin 3 to zero. But then the gate has to be much more negative than C800 (and thus the drain) and the difference increases when the output voltage amplitude (and pin 6 are higher. (Or, when a load is attached at some Ampl setting, the difference between drain and gate decreases.)
I was a bit surprised by this when I did measurements in my PG506. Only one situation so far: unloaded, output amplitude set to 6 V:
"-72V" was about -21 V,
gate about -12.5 V,
drain about -7 V. when on, slightly positive when off.

When your unloaded "-72V" doesn't change with Ampl setting then something is really wrong. Could be the opamp U840, or open Q800, open Q792, you name it...
Possibly the fasted way to find the fault(s) is to check as far as possible, without desoldering, all transistors and diodes with the DMM diode check function . You might be lucky!

Albert

On Sat, Jun 8, 2019 at 11:56 PM, Mlynch001 wrote:


Albert,

You are so right in saying that there are a lot of potential faults. I'm just
happy that I got it back to the point where I am at the moment. If we can
take it one step at a time and in an organized manner, I believe that will
yield the best results. Similar to the 100V supply, once I can zero in on a
specific area, I will have a better chance of locating the problem. All of
these current and voltage regulators just give me chills. Wondering how many
of these might be bad?

Here are the results from the output of the High Amplitude section:

PG506 Settings
Function High Ampl
Period 1uS 1 MHz
Variable Full ccw
Pulse Amplitude MAX

Scope TDS460A

Channel 1 DC Coupling into 1 M Ohm

Used "AUTOSET"

Screen readout shows -63.52 DCV No wave form is visible, checked both AC
and DC Coupled.

Channel 1 DC Coupled into 1 M Ohm channel with 50Ohm termination. .1 uSec 2V
range

Single linear trace at just under -3 1/4 divisions and readout shows -6.45
DCV.

VARIABLE Knob has no effect on the voltage level present.

R790 has no affect on voltage.

Switching PERIOD to other ranges does not affect affect the voltage.

I hope this all makes sense. If not, feel free to ask questions and correct
me as needed.

I sincerely appreciate your guidance and advice.
--
Michael Lynch
Dardanelle, AR


Re: TDS 620A vs. TDS 620B questions and repair inquiry

David Berlind
 

As I await all your answers, I started with page 1 of the manual this morning and am liking the functionality. Compared to my initial quick-plug-it-in see if it works the other day, things went much better. The first thing I did was a factory reset (following the manual's instructions of course). This may have fixed a few things. Working with the probe calibration signal, here's a video of what I observed after selecting some measurements for display. I'm using some100Mhz probes at 1x.

https://photos.app.goo.gl/8Lt8pPpUCVgPPUw1A

On June 9, 2019 11:42:15 AM "Stephen Hanselman" <kc4sw.io@kc4sw.com> wrote:

I don’t have a lot of knowledge but two things. In the 540, 540A, 540C, etc the “ “ and “A” speak a different HPIB language from the “B” and “C”. If a lab says calibration for $300 they “may” hook it up and make sure the readings are close but not much else.

I don’t know what a fully automated set could do, I do all my calibrations manually with the Tek software. The 540B takes about 5 hours to do a good job. If you were close I say bring it by and turn you loose on my software.

Regards,

Stephen Hanselman
Datagate Systems, LLC
3107 North Deer Run Road #24
Carson City, Nevada, 89701
(775) 882-5117 office
(775) 720-6020 mobile
s.hanselman@datagatesystems.com
www.datagatesystems.com
a Service Disabled, Veteran Owned Small Business
DISCLAIMER:
This e-mail and any attachments are intended only for use by the addressee(s) named herein and may contain legally privileged and/or proprietary information. If you are not the intended recipient, any dissemination, distribution or copying of this e-mail and any attachments is strictly prohibited. If you have received this e-mail in error, please immediately notify me and permanently delete the original and all copies and printouts of this e-mail and any attachments.
On Jun 9, 2019, at 08:25, David Berlind <david@berlind.org> wrote:


Hi all,


After starting my oscilloscope journey with analog scopes for the last two years and seeing some of what the digital scopes could do (for example, maths), I had been watching my local marketplaces carefully for a good price on a digital scope in working condition. I recently picked up at TDS 620B for $85 and am now beginning the journey of getting to know it. I will be posting video of its behavior which I think may be in need of correction based on initial observations.. and I am of course looking for advice. But I may be wrong about that. I will work on eliminating other issues first (configuration, line noise, etc.).


My first inquiry involves four questions:


1. I could not locate an online manual for the 620B. I found the Technical Reference and printed that out. But in terms of the User Manual, I could only find a manual for the 620A (could just be bad Googling skills). So, I downloaded and printed that out. Now, I'm trying to ascertain whether the 620A manual is for the most part applicable (should have done this before killing a tree to print it I guess) or whether the 620A is different enough from the 620B that the manual doesn't apply. I've been looking for some way to compare the two side by side (I found some differently formatted data and specification sheets so apples to apples isn't perfect, but there's some overlapping data to get some jist). But I thought it would be prudent to toss the question out to this group because maybe someone will just know and can summarize key differences and how that impacts anything (usage, probes, etc).


2. I'll take any suggestions from you pros on great ways to get started with this scope. Configurations to try. Shortcuts. Anything that will fast-track my introduction to expert operation of the scope.


3. The 620B did not come with any probes when I purchased it. I noticed from the 620A documentation that that scope originally came with a 6139A probe which lead me into an exploration of probe characteristics. That probe's specs appear to match the 500Mhz capability of the scope. Over the last two years, I haven't thought much about the probes themselves. Just been using what I acquired along the way and things seem to work. So, in the spirit of rooting out any configuration problems before needing to effect any repairs, to what extent could basic probe differences impact behavior? For example, I have some basic 1X/10x probes (which might not be rated for 500Mhz) that work nicely on my 7603. What incompatibilities could exist between these probes and the 620B such that I might get unexpected/inaccurate behavior?


4. Wondering whether it might be best and faster just to have the pros take a look at the scope, I have inquired with a local calibration service as to the cost of a "tune-up." The estimate just for calibration for was over $300 (way more than the cost of the scope). It dawned on me that one option might be to pay someone in this group to bring her up to snuff. This is for hobbyist work (repairing amps, radios, etc) so it's not like I need a certificate. Is there someone here who does that sort of thing?


Thank you.


David


Re: TDS 620A vs. TDS 620B questions and repair inquiry

David Berlind
 

Thanks Stephen. Unfortunately, I'm in Boston. Googling HPIB now.

On June 9, 2019 11:42:15 AM "Stephen Hanselman" <kc4sw.io@kc4sw.com> wrote:

I don’t have a lot of knowledge but two things. In the 540, 540A, 540C, etc the “ “ and “A” speak a different HPIB language from the “B” and “C”. If a lab says calibration for $300 they “may” hook it up and make sure the readings are close but not much else.

I don’t know what a fully automated set could do, I do all my calibrations manually with the Tek software. The 540B takes about 5 hours to do a good job. If you were close I say bring it by and turn you loose on my software.

Regards,

Stephen Hanselman
Datagate Systems, LLC
3107 North Deer Run Road #24
Carson City, Nevada, 89701
(775) 882-5117 office
(775) 720-6020 mobile
s.hanselman@datagatesystems.com
www.datagatesystems.com
a Service Disabled, Veteran Owned Small Business
DISCLAIMER:
This e-mail and any attachments are intended only for use by the addressee(s) named herein and may contain legally privileged and/or proprietary information. If you are not the intended recipient, any dissemination, distribution or copying of this e-mail and any attachments is strictly prohibited. If you have received this e-mail in error, please immediately notify me and permanently delete the original and all copies and printouts of this e-mail and any attachments.
On Jun 9, 2019, at 08:25, David Berlind <david@berlind.org> wrote:


Hi all,


After starting my oscilloscope journey with analog scopes for the last two years and seeing some of what the digital scopes could do (for example, maths), I had been watching my local marketplaces carefully for a good price on a digital scope in working condition. I recently picked up at TDS 620B for $85 and am now beginning the journey of getting to know it. I will be posting video of its behavior which I think may be in need of correction based on initial observations.. and I am of course looking for advice. But I may be wrong about that. I will work on eliminating other issues first (configuration, line noise, etc.).


My first inquiry involves four questions:


1. I could not locate an online manual for the 620B. I found the Technical Reference and printed that out. But in terms of the User Manual, I could only find a manual for the 620A (could just be bad Googling skills). So, I downloaded and printed that out. Now, I'm trying to ascertain whether the 620A manual is for the most part applicable (should have done this before killing a tree to print it I guess) or whether the 620A is different enough from the 620B that the manual doesn't apply. I've been looking for some way to compare the two side by side (I found some differently formatted data and specification sheets so apples to apples isn't perfect, but there's some overlapping data to get some jist). But I thought it would be prudent to toss the question out to this group because maybe someone will just know and can summarize key differences and how that impacts anything (usage, probes, etc).


2. I'll take any suggestions from you pros on great ways to get started with this scope. Configurations to try. Shortcuts. Anything that will fast-track my introduction to expert operation of the scope.


3. The 620B did not come with any probes when I purchased it. I noticed from the 620A documentation that that scope originally came with a 6139A probe which lead me into an exploration of probe characteristics. That probe's specs appear to match the 500Mhz capability of the scope. Over the last two years, I haven't thought much about the probes themselves. Just been using what I acquired along the way and things seem to work. So, in the spirit of rooting out any configuration problems before needing to effect any repairs, to what extent could basic probe differences impact behavior? For example, I have some basic 1X/10x probes (which might not be rated for 500Mhz) that work nicely on my 7603. What incompatibilities could exist between these probes and the 620B such that I might get unexpected/inaccurate behavior?


4. Wondering whether it might be best and faster just to have the pros take a look at the scope, I have inquired with a local calibration service as to the cost of a "tune-up." The estimate just for calibration for was over $300 (way more than the cost of the scope). It dawned on me that one option might be to pay someone in this group to bring her up to snuff. This is for hobbyist work (repairing amps, radios, etc) so it's not like I need a certificate. Is there someone here who does that sort of thing?


Thank you.


David


Re: 7854 with strange intensity/focus problem (to me)

unclebanjoman
 

I've just tried to disconnect the P83 connector from Z-axis board (focus & Z signals): the beam become barely visible and unfocused; readout is invisible.

Max


Re: TDS 620A vs. TDS 620B questions and repair inquiry

Stephen Hanselman
 

I don’t have a lot of knowledge but two things. In the 540, 540A, 540C, etc the “ “ and “A” speak a different HPIB language from the “B” and “C”. If a lab says calibration for $300 they “may” hook it up and make sure the readings are close but not much else.

I don’t know what a fully automated set could do, I do all my calibrations manually with the Tek software. The 540B takes about 5 hours to do a good job. If you were close I say bring it by and turn you loose on my software.

Regards,

Stephen Hanselman
Datagate Systems, LLC
3107 North Deer Run Road #24
Carson City, Nevada, 89701
(775) 882-5117 office
(775) 720-6020 mobile
s.hanselman@datagatesystems.com
www.datagatesystems.com
a Service Disabled, Veteran Owned Small Business
DISCLAIMER:
This e-mail and any attachments are intended only for use by the addressee(s) named herein and may contain legally privileged and/or proprietary information. If you are not the intended recipient, any dissemination, distribution or copying of this e-mail and any attachments is strictly prohibited. If you have received this e-mail in error, please immediately notify me and permanently delete the original and all copies and printouts of this e-mail and any attachments.

On Jun 9, 2019, at 08:25, David Berlind <david@berlind.org> wrote:

Hi all,

After starting my oscilloscope journey with analog scopes for the last two years and seeing some of what the digital scopes could do (for example, maths), I had been watching my local marketplaces carefully for a good price on a digital scope in working condition. I recently picked up at TDS 620B for $85 and am now beginning the journey of getting to know it. I will be posting video of its behavior which I think may be in need of correction based on initial observations.. and I am of course looking for advice. But I may be wrong about that. I will work on eliminating other issues first (configuration, line noise, etc.).

My first inquiry involves four questions:

1. I could not locate an online manual for the 620B. I found the Technical Reference and printed that out. But in terms of the User Manual, I could only find a manual for the 620A (could just be bad Googling skills). So, I downloaded and printed that out. Now, I'm trying to ascertain whether the 620A manual is for the most part applicable (should have done this before killing a tree to print it I guess) or whether the 620A is different enough from the 620B that the manual doesn't apply. I've been looking for some way to compare the two side by side (I found some differently formatted data and specification sheets so apples to apples isn't perfect, but there's some overlapping data to get some jist). But I thought it would be prudent to toss the question out to this group because maybe someone will just know and can summarize key differences and how that impacts anything (usage, probes, etc).

2. I'll take any suggestions from you pros on great ways to get started with this scope. Configurations to try. Shortcuts. Anything that will fast-track my introduction to expert operation of the scope.

3. The 620B did not come with any probes when I purchased it. I noticed from the 620A documentation that that scope originally came with a 6139A probe which lead me into an exploration of probe characteristics. That probe's specs appear to match the 500Mhz capability of the scope. Over the last two years, I haven't thought much about the probes themselves. Just been using what I acquired along the way and things seem to work. So, in the spirit of rooting out any configuration problems before needing to effect any repairs, to what extent could basic probe differences impact behavior? For example, I have some basic 1X/10x probes (which might not be rated for 500Mhz) that work nicely on my 7603. What incompatibilities could exist between these probes and the 620B such that I might get unexpected/inaccurate behavior?

4. Wondering whether it might be best and faster just to have the pros take a look at the scope, I have inquired with a local calibration service as to the cost of a "tune-up." The estimate just for calibration for was over $300 (way more than the cost of the scope). It dawned on me that one option might be to pay someone in this group to bring her up to snuff. This is for hobbyist work (repairing amps, radios, etc) so it's not like I need a certificate. Is there someone here who does that sort of thing?

Thank you.

David



Re: TDS 620A vs. TDS 620B questions and repair inquiry

David Berlind
 

Great pointers Harvey. Thank you and looking forward to more. In partial answer to my first question, as I pour through the two very differently format data sheets that I have (one that includes the 620A and the other includes the 620B), I suddenly noticed that the data sheet that includes the 620B also includes the 640A with some side by side comparisons of some specs. Does someone know if the 640A is identical to the 620A except for the 4 vs. 2 channels? If so, that gives me a couple of ideas on how the 620A differs from the 620B differ and on what topics the manual for the 620A might be different.

On June 9, 2019 11:03:01 AM "Harvey White" <madyn@dragonworks.info> wrote:

On 6/9/2019 10:25 AM, David Berlind wrote:
Hi all,

After starting my oscilloscope journey with analog scopes for the last two years and seeing some of what the digital scopes could do (for example, maths), I had been watching my local marketplaces carefully for a good price on a digital scope in working condition. I recently picked up at TDS 620B for $85 and am now beginning the journey of getting to know it. I will be posting video of its behavior which I think may be in need of correction based on initial observations.. and I am of course looking for advice. But I may be wrong about that. I will work on eliminating other issues first (configuration, line noise, etc.).
Nice price.


My first inquiry involves four questions:

1. I could not locate an online manual for the 620B. I found the Technical Reference and printed that out. But in terms of the User Manual, I could only find a manual for the 620A (could just be bad Googling skills). So, I downloaded and printed that out. Now, I'm trying to ascertain whether the 620A manual is for the most part applicable (should have done this before killing a tree to print it I guess) or whether the 620A is different enough from the 620B that the manual doesn't apply. I've been looking for some way to compare the two side by side (I found some differently formatted data and specification sheets so apples to apples isn't perfect, but there's some overlapping data to get some jist). But I thought it would be prudent to toss the question out to this group because maybe someone will just know and can summarize key differences and how that impacts anything (usage, probes, etc).
This I can't help with, I have neither.
2. I'll take any suggestions from you pros on great ways to get started with this scope. Configurations to try. Shortcuts. Anything that will fast-track my introduction to expert operation of the scope.
There's an auto set (or should be) that tries to guess at the proper
settings for a waveform, it's a place to start.

I always start at the highest sweep speed (for an unknown waveform) and
go down. Put in a 100 Khz sine wave, for instance, set the sweep
appropriately, then start slowing the sweep down. You'll reach a point
where you duplicate the original waveform, but at a very wrong sweep
speed. Has to do with sampling and waveform reconstruction.


3. The 620B did not come with any probes when I purchased it. I noticed from the 620A documentation that that scope originally came with a 6139A probe which lead me into an exploration of probe characteristics. That probe's specs appear to match the 500Mhz capability of the scope. Over the last two years, I haven't thought much about the probes themselves. Just been using what I acquired along the way and things seem to work. So, in the spirit of rooting out any configuration problems before needing to effect any repairs, to what extent could basic probe differences impact behavior? For example, I have some basic 1X/10x probes (which might not be rated for 500Mhz) that work nicely on my 7603. What incompatibilities could exist between these probes and the 620B such that I might get unexpected/inaccurate behavior?
No real incompatibilities, except that your average X1 probe is lucky to
get to a 1 Mhz bandwidth, and your average X10 probe (unless otherwise
noted) is about 100 to 200 Mhz if that. Google Tektronix probe
information (or the Tek wiki) and that will give you the bandwidth. The
limitation is in the probe, not the scope.

Note that the average x1/x10 is made for a 1 meg ohm input impedance
scope, and the circuit sees (at DC only) 1 or 10 Megohms. A 50 ohm
probe if at X1, would need a 50 ohm input impedance at the scope, and
the circuit would see 50 ohms DC. An X10 would need the same 50 ohm
input impedance, but the circuit would see 500 ohms.

I say DC because at higher frequencies, the capacitive loading of the
probe predominates. Given that a 50 ohm and 1 megohm probe have the
same capacitive loading, the effect of that impedance across 50 ohms is
far less than across 1 meg, and the 50 ohm probe would have higher
bandwidth.

50 ohm x10 probes can be successfully used on TTL and some CMOS circuits
where the resistive effect predominates normally.


These probes are passive, not active (no transistors inside), for active
probes, that's a different discussion.



4. Wondering whether it might be best and faster just to have the pros take a look at the scope, I have inquired with a local calibration service as to the cost of a "tune-up." The estimate just for calibration for was over $300 (way more than the cost of the scope). It dawned on me that one option might be to pay someone in this group to bring her up to snuff. This is for hobbyist work (repairing amps, radios, etc) so it's not like I need a certificate. Is there someone here who does that sort of thing?
There are, but if you're not in the continental US (and perhaps even if
you are), shipping may be prohibitive even if the service would be free.

There are a number of performance "checks" in the manual. Doing them as
best you can will tell you if the scope needs any calibration, and will
also indicate how close you are to that mythical "calibrated".

Harvey


Thank you.

David





Re: TDS 620A vs. TDS 620B questions and repair inquiry

Harvey White
 

On 6/9/2019 10:25 AM, David Berlind wrote:
Hi all,

After starting my oscilloscope journey with analog scopes for the last two years and seeing some of what the digital scopes could do (for example, maths), I had been watching my local marketplaces carefully for a good price on a digital scope in working condition. I recently picked up at TDS 620B for $85 and am now beginning the journey of getting to know it. I will be posting video of its behavior which I think may be in need of correction based on initial observations.. and I am of course looking for advice. But I may be wrong about that. I will work on eliminating other issues first (configuration, line noise, etc.).
Nice price.


My first inquiry involves four questions:

1. I could not locate an online manual for the 620B. I found the Technical Reference and printed that out. But in terms of the User Manual, I could only find a manual for the 620A (could just be bad Googling skills). So, I downloaded and printed that out. Now, I'm trying to ascertain whether the 620A manual is for the most part applicable (should have done this before killing a tree to print it I guess) or whether the 620A is different enough from the 620B that the manual doesn't apply. I've been looking for some way to compare the two side by side (I found some differently formatted data and specification sheets so apples to apples isn't perfect, but there's some overlapping data to get some jist). But I thought it would be prudent to toss the question out to this group because maybe someone will just know and can summarize key differences and how that impacts anything (usage, probes, etc).
This I can't help with, I have neither.
2. I'll take any suggestions from you pros on great ways to get started with this scope. Configurations to try. Shortcuts. Anything that will fast-track my introduction to expert operation of the scope.
There's an auto set (or should be) that tries to guess at the proper settings for a waveform, it's a place to start.

I always start at the highest sweep speed (for an unknown waveform) and go down.  Put in a 100 Khz sine wave, for instance, set the sweep appropriately, then start slowing the sweep down. You'll reach a point where you duplicate the original waveform, but at a very wrong sweep speed.  Has to do with sampling and waveform reconstruction.


3. The 620B did not come with any probes when I purchased it. I noticed from the 620A documentation that that scope originally came with a 6139A probe which lead me into an exploration of probe characteristics. That probe's specs appear to match the 500Mhz capability of the scope. Over the last two years, I haven't thought much about the probes themselves. Just been using what I acquired along the way and things seem to work. So, in the spirit of rooting out any configuration problems before needing to effect any repairs, to what extent could basic probe differences impact behavior? For example, I have some basic 1X/10x probes (which might not be rated for 500Mhz) that work nicely on my 7603. What incompatibilities could exist between these probes and the 620B such that I might get unexpected/inaccurate behavior?
No real incompatibilities, except that your average X1 probe is lucky to get to a 1 Mhz bandwidth, and your average X10 probe (unless otherwise noted) is about 100 to 200 Mhz if that.  Google Tektronix probe information (or the Tek wiki) and that will give you the bandwidth.  The limitation is in the probe, not the scope.

Note that the average x1/x10 is made for a 1 meg ohm input impedance scope, and the circuit sees (at DC only) 1 or 10 Megohms.  A 50 ohm probe if at X1, would need a 50 ohm input impedance at the scope, and the circuit would see 50 ohms DC.  An X10 would need the same 50 ohm input impedance, but the circuit would see 500 ohms.

I say DC because at higher frequencies, the capacitive loading of the probe predominates.  Given that a 50 ohm and 1 megohm probe have the same capacitive loading, the effect of that impedance across 50 ohms is far less than across 1 meg, and the 50 ohm probe would have higher bandwidth.

50 ohm x10 probes can be successfully used on TTL and some CMOS circuits where the resistive effect predominates normally.


These probes are passive, not active (no transistors inside), for active probes, that's a different discussion.



4. Wondering whether it might be best and faster just to have the pros take a look at the scope, I have inquired with a local calibration service as to the cost of a "tune-up." The estimate just for calibration for was over $300 (way more than the cost of the scope). It dawned on me that one option might be to pay someone in this group to bring her up to snuff. This is for hobbyist work (repairing amps, radios, etc) so it's not like I need a certificate. Is there someone here who does that sort of thing?
There are, but if you're not in the continental US (and perhaps even if you are), shipping may be prohibitive even if the service would be free.

There are a number of performance "checks" in the manual.  Doing them as best you can will tell you if the scope needs any calibration, and will also indicate how close you are to that mythical "calibrated".

Harvey


Thank you.

David




TDS 620A vs. TDS 620B questions and repair inquiry

David Berlind
 

Hi all,

After starting my oscilloscope journey with analog scopes for the last two years and seeing some of what the digital scopes could do (for example, maths), I had been watching my local marketplaces carefully for a good price on a digital scope in working condition. I recently picked up at TDS 620B for $85 and am now beginning the journey of getting to know it. I will be posting video of its behavior which I think may be in need of correction based on initial observations.. and I am of course looking for advice. But I may be wrong about that. I will work on eliminating other issues first (configuration, line noise, etc.).

My first inquiry involves four questions:

1. I could not locate an online manual for the 620B. I found the Technical Reference and printed that out. But in terms of the User Manual, I could only find a manual for the 620A (could just be bad Googling skills). So, I downloaded and printed that out. Now, I'm trying to ascertain whether the 620A manual is for the most part applicable (should have done this before killing a tree to print it I guess) or whether the 620A is different enough from the 620B that the manual doesn't apply. I've been looking for some way to compare the two side by side (I found some differently formatted data and specification sheets so apples to apples isn't perfect, but there's some overlapping data to get some jist). But I thought it would be prudent to toss the question out to this group because maybe someone will just know and can summarize key differences and how that impacts anything (usage, probes, etc).

2. I'll take any suggestions from you pros on great ways to get started with this scope. Configurations to try. Shortcuts. Anything that will fast-track my introduction to expert operation of the scope.

3. The 620B did not come with any probes when I purchased it. I noticed from the 620A documentation that that scope originally came with a 6139A probe which lead me into an exploration of probe characteristics. That probe's specs appear to match the 500Mhz capability of the scope. Over the last two years, I haven't thought much about the probes themselves. Just been using what I acquired along the way and things seem to work. So, in the spirit of rooting out any configuration problems before needing to effect any repairs, to what extent could basic probe differences impact behavior? For example, I have some basic 1X/10x probes (which might not be rated for 500Mhz) that work nicely on my 7603. What incompatibilities could exist between these probes and the 620B such that I might get unexpected/inaccurate behavior?

4. Wondering whether it might be best and faster just to have the pros take a look at the scope, I have inquired with a local calibration service as to the cost of a "tune-up." The estimate just for calibration for was over $300 (way more than the cost of the scope). It dawned on me that one option might be to pay someone in this group to bring her up to snuff. This is for hobbyist work (repairing amps, radios, etc) so it's not like I need a certificate. Is there someone here who does that sort of thing?

Thank you.

David


Re: 7854 with strange intensity/focus problem (to me)

unclebanjoman
 

On Sat, Jun 8, 2019 at 11:37 PM, Raymond Domp Frank wrote:


On Sat, Jun 8, 2019 at 10:09 PM, unclebanjoman wrote:


My suspect is toward the HV multiplier (152-0716-00). I don't think a
damaged
(or exhausted) CRT can be the cause. Or maybe yes?
1) - Did you check the (low) voltage supplies *at A20* (the HV board)?
Yes, they are all correct (checked at P20 connector)

2) - Do all intensity pots have equal influence on focus in all areas
(trace/readout/digital) combined?
Yes

3) - I would not exclude leakage in the HV (focus, DC restorer) chains. I got the
impression that the external focus pots in my 7854's have a bit less influence
than in some other 'scopes.
I would like to check some voltages on the DC restorers circuit but I don't know how to remove the A20 board safely to reach the components mounted on it ...
I think it would be helpful to be able to measure the voltages on the grids.

4) - The focus and Z-axis circuits in the 7854 are more complicated than in many
other 'scopes, with all kinds of circuits meant to improve focus tracking. You
may have an issue there somewhere. To get an indication, you may want to check
if playing a bit with CRT bias (affecting overall beam intensity) at higher
Intensity settings has the same (detrimental) effect as turning Intensity up
further. The CRT bias adjustment sits after most of the (possibly problematic)
Z-axis circuits. It's easy to interactively re-adjust CRT bias later and it
doesn't influence calibration status.
Playing with the CRT bias adjustment (R65) has the same effect: the trace intensity increases a little, then becomes more darker and very unfocused. Readout and digital trace become almost invisible.

5) - It's not unthinkable that someone before you has made incorrect adjustments
in the Z-axis/focus circuits. Easily done: have a look at D4 (Z-axis level) on
dwg 4 (A14, mainframe logic) and where that comes from (HV multiplier) as an
example...
I performed all the check/adjustment procedure as detailed in the manual, section B (Z-axis and display). All waveforms and voltage levels on A21 and A14 boards are corrects and in perfect compliance with those reported on the manual. No adjustment was necessary. Axis level is 80 mV p-p as it should be.

6) - The HV multiplier voltage, as long as it outputs a reasonable HV has little
dynamic influence on focusing so I wouldn't initially suspect it in this case.
You may temporarily disconnect PDA voltage and check (carefully, both to
protect yourself and the circuits); you'll still have an image but darker,
probably larger and less focused but the dependency on the intensity pots can
be judged.
Disconnecting the PDA jack, the trace become more darker and horizontally compressed. Readout and digital trace become invisible even with the intensity pot fully CW. Turning the intensity pot to the max has the same effect previously described: intensity dims and the trace becomes more unfocused. No readout or digital trace visibly at all.

Max


Waveform calculator keyboard spotted for sale at an electronics fair

 

Since those are somewhat hard to find, I thought I would let you guys know.
I am not sure where exactly this is, but the author of the photo can be
reached.

https://mobile.twitter.com/Foone/status/1137383704521633795


Re: PG506 ISSUES Need some experienced minds!

Mlynch001
 

Albert,

You are so right in saying that there are a lot of potential faults. I'm just happy that I got it back to the point where I am at the moment. If we can take it one step at a time and in an organized manner, I believe that will yield the best results. Similar to the 100V supply, once I can zero in on a specific area, I will have a better chance of locating the problem. All of these current and voltage regulators just give me chills. Wondering how many of these might be bad?

Here are the results from the output of the High Amplitude section:

PG506 Settings
Function High Ampl
Period 1uS 1 MHz
Variable Full ccw
Pulse Amplitude MAX

Scope TDS460A

Channel 1 DC Coupling into 1 M Ohm

Used "AUTOSET"

Screen readout shows -63.52 DCV No wave form is visible, checked both AC and DC Coupled.

Channel 1 DC Coupled into 1 M Ohm channel with 50Ohm termination. .1 uSec 2V range

Single linear trace at just under -3 1/4 divisions and readout shows -6.45 DCV.

VARIABLE Knob has no effect on the voltage level present.

R790 has no affect on voltage.

Switching PERIOD to other ranges does not affect affect the voltage.

I hope this all makes sense. If not, feel free to ask questions and correct me as needed.

I sincerely appreciate your guidance and advice.
--
Michael Lynch
Dardanelle, AR


Re: 7854 with strange intensity/focus problem (to me)

 

On Sat, Jun 8, 2019 at 10:09 PM, unclebanjoman wrote:


My suspect is toward the HV multiplier (152-0716-00). I don't think a damaged
(or exhausted) CRT can be the cause. Or maybe yes?
- Did you check the (low) voltage supplies *at A20* (the HV board)?
- Do all intensity pots have equal influence on focus in all areas (trace/readout/digital) combined?
- I would not exclude leakage in the HV (focus, DC restorer) chains. I got the impression that the external focus pots in my 7854's have a bit less influence than in some other 'scopes.
- The focus and Z-axis circuits in the 7854 are more complicated than in many other 'scopes, with all kinds of circuits meant to improve focus tracking. You may have an issue there somewhere. To get an indication, you may want to check if playing a bit with CRT bias (affecting overall beam intensity) at higher Intensity settings has the same (detrimental) effect as turning Intensity up further. The CRT bias adjustment sits after most of the (possibly problematic) Z-axis circuits. It's easy to interactively re-adjust CRT bias later and it doesn't influence calibration status.
- It's not unthinkable that someone before you has made incorrect adjustments in the Z-axis/focus circuits. Easily done: have a look at D4 (Z-axis level) on dwg 4 (A14, mainframe logic) and where that comes from (HV multiplier) as an example...
- The HV multiplier voltage, as long as it outputs a reasonable HV has little dynamic influence on focusing so I wouldn't initially suspect it in this case. You may temporarily disconnect PDA voltage and check (carefully, both to protect yourself and the circuits); you'll still have an image but darker, probably larger and less focused but the dependency on the intensity pots can be judged.

Raymond


7854 with strange intensity/focus problem (to me)

unclebanjoman
 

I got another 7854 scope to check and eventually re-calibrate.
The scope is in very nice conditions, with options 03 and 2D installed. Fully functional. Serial No. B063304.
Its interior shows no signs of tampering or repairs. Completely virgin.

It exhibits a poor intensity and focus control. I try to explain better.
The display shows up with normal intensity with the intensity control approx. 10-11 o'clock, as usually should be.
Slowly turning the intensity control more CW the trace's intensity increases but not enough, and the focus becomes quite poor. Same symptom happens to the readout display.
The focus control has little effect.

Quickly turning the intensity from zero (fully CCW) to the max (fully clockwise), the trace first increases in intensity and then quickly darkens and becomes very blurred. As if the multiplier (or some HV voltage) sat down.

All the voltages are in range. I checked the cathode voltage also, reading -2957 V., with no change turning the intensity pot from one extreme to the other.

My suspect is toward the HV multiplier (152-0716-00). I don't think a damaged (or exhausted) CRT can be the cause. Or maybe yes?

Any ideas?

Thanks in advance for your suggestions.
Max


Re: PG506 ISSUES Need some experienced minds!

Albert Otten
 

Michael,

We all make mistakes. Nice of this forum is that nobody hesitates to confess this. Good that 2 functions are working now. (You will love the PG506 once it's fully operational.)
Now about the bad High Amp output. I think most likely the fault is in the "-72V" regulation. You verified 72 V in the Stand Amp mode, but in High Amp mode the actual supply voltage depends on the Amp knob setting. I would check the actual voltage with a scope since there could be oscillations in the feedback circuit.
I'd better not speculate what a next step could be if the actual voltage is weird. There are so many possible faults. Let's see what your findings are.

Albert

On Sat, Jun 8, 2019 at 06:11 PM, Mlynch001 wrote:


Albert,

ROFL, you are absolutely correct. Switch was actually coming apart, the metal
top retainer was partially installed, I tightened that up and now it works.
The full height wave that I was seeing was evidently me mis-using my TDS 460A
monitor scope. I hooked up my trusty 465B this AM, with a 50Ohm termination,
DC coupled and confirmed that I was full of crap when I wrote the previous
post. The fast rise works EXACTLY as you said it should. My mistake: So. .
. We have some serious progress now that you have backed me off the edge of
the cliff. I did find that the High Amplitude setting does indeed respond to
the Period control and the Variable knob . Just a really ugly semi square
wave with lots of what I would call “noise” over top. Thanks for the
lesson! Now to get this other stuff corrected.

--
Michael Lynch
Dardanelle, AR


Re: PG506 ISSUES Need some experienced minds!

Mlynch001
 

Albert,

ROFL, you are absolutely correct. Switch was actually coming apart, the metal top retainer was partially installed, I tightened that up and now it works. The full height wave that I was seeing was evidently me mis-using my TDS 460A monitor scope. I hooked up my trusty 465B this AM, with a 50Ohm termination, DC coupled and confirmed that I was full of crap when I wrote the previous post. The fast rise works EXACTLY as you said it should. My mistake: So. . . We have some serious progress now that you have backed me off the edge of the cliff. I did find that the High Amplitude setting does indeed respond to the Period control and the Variable knob . Just a really ugly semi square wave with lots of what I would call “noise” over top. Thanks for the lesson! Now to get this other stuff corrected.

--
Michael Lynch
Dardanelle, AR


Re: PG506 ISSUES Need some experienced minds!

Albert Otten
 

Let me first address these problems (from your much longer message).


Now the Negative part. My Fast Rise board now shows a full height square wave;
instead of a negative or positive going signal starting at the zero volt line,
as would be normal. Both outputs show the same, full sized square wave.
Perfect shape, but basically both halves of the signal combined at either
output.
In my opinion it's impossible that you get a "full height" square wave in the sense that both outputs jump between some positive value and the opposite negative value. The outputs are clamped by diodes which prevents them to be driven in the wrong direction from ground. Moreover, the output transistors can only pull to their own supply, positive for one and negative for the other.
I guess that you judged this with the scope AC coupled (so you have no zero reference) and forgot to use a 50R termination?


Also, my DC switch quit working
That can only be due to a dirty switch S660 or U610A not listinging to its clear input, isn't it?

Albert

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