Topics

My 2465B has arrived + A5 Board leaky caps cleanup

 

On Sat, Nov 24, 2018 at 06:15 PM, Roger Evans wrote:


If you add 30 - 50cms of 50 ohm coax between the avalanche transistor
collector and ground you will get a nice flat top pulse
Yes, if you make sure that impedances match. With your 'scope, you'll have no way to check that (overshoot, undershoot, ringing) but what you'll "measure" very likely will be closer to a rise time than without the so-called "charge line" and as roger describes it, it's very easy to do.

Raymond

Roger Evans
 

If you add 30 - 50cms of 50 ohm coax between the avalanche transistor collector and ground you will get a nice flat top pulse with duration twice the transit time of the coax. It does make the avalanche generator a little clumsy and you can find designs that etch a 50 ohm serpentine transmission line onto the pulse generator PCB.

Roger

 

On Fri, Nov 23, 2018 at 01:59 PM, <tekscopegroup@...> wrote:


Added 4 pictures to my photo album showing rise time measurements of the 2465B
(o.57nS) and also my 2247A (~2.0nS). BTW the 0.57nS rise time was confirmed
with the corresponding parametric measurement, the result was exactly 0.57nS
as well.
That's not rise time you're seeing or "measuring", it's more like slew rate and what looks like the amplitude of the pulse really isn't.
Rise time is measured between two *stable levels* (usually, between 10% and 90% levels of it), whereas your generator generates a pulse with a duration that is relatively short as compared against the 'scope's rise time. On a faster 'scope you'll see a larger amplitude than on your 2465B, more towards the actual pulse amplitude. The parametric measurement assumes you're providing a step voltage; it cannot see the shortness of your pulse.
A pulse generator is not suitable to measure rise time, unless the pulse stays on its steady levels long enough, i.e. at least 2 ns or so for the 2465B.
A realistic rise time with an infinitely fast step applied would be more like 0.8 ns for the 2465B.
Assuming a theoretical rise time of your pulse generator of 0 ns (!), your 2465B's BW would be over 600 MHz. Even with Tek's usual conservative specs, 600 MHz + is not realistic.

Likewise, 2 ns for your 100 MHz-specified 2247A is not realistic. It would imply a BW of 175 MHz.

Just for fun, compare the amplitude as shown on both 'scopes. Don't forget to put both 'scope's vertical sensitivity settings out of "variable" for that.

What you *can* conclude is that the pulse slews faster than both your 'scopes.

Raymond

Harvey White
 

On Fri, 23 Nov 2018 04:26:56 -0800, you wrote:


For measuring AC ripple at 120 Hz, I'd look at the ripple, but
triggered on line. Measure anything that stands still....

Ought to get you close.

Harvey



On Tue, Nov 6, 2018 at 08:03 AM, Chuck Harris wrote:
Hey! Don't muck with the DAC adjustment, unless you are prepared
to do a full calibration!

It is not supposed to be +1.25 and -1.25 volts, but rather a 2.500V span.

Sure, if you are a perfectionist, and diddle with the 10K reference
resistor values, and put in perfect opamps, it can achieve those values,
but that is not a necessary goal: 2.500V span when doing the calibration
routine is the necessary goal. -1.25 and +1.36V references that are *stable*
is the goal, as any errors in them get stored in the calibration constants,
and as such calibrated out, when the scope is calibrated.

Any tweaking, or replacement of DAC parts that you do will require a
full calibration of your scope. Why? Because you have no idea what they
were like when it was last calibrated.

If they were on the low (or high) side of spec when last calibrated, and
you adjust them to be right on, with a DVM that was on the high (low) side
of spec), they errors could add up to be wrong enough to perform poorly.

-Chuck Harris
OK understood. I have not touched the adjustment at R2010. Only replaced both 10K 0.1% resistors (the original ones where both open). Also replaced R2016 1K 1% because I pulled it out by mistake and one of the contacts looked a bit iffy, so that one was also needing replacement anyway. The original value of this last resistor checked on my HP3478A was 1.00248K and the substitute measured 1.00302K, so only a 0.0539% difference between them. The voltages from the +1.36 and -1.25 references did not vary very much from what the where while still using the temporary 5% resistors. I initially had +1.3848 and now it is 1.3836v. And -1.2688 went to -1.2681v. Not much of a difference.

I was looking at the procedure to check the 2.5V DAC voltage span in the service manual (page 5-3) and plan on verifying it at pin 13 of J119. But I will not be making any adjustments to it, since as explained above this might actually be detrimental and worsen the calibration state of the scope. So for now I will only record the voltage range, and they will stay as is.

I have received my new GQ-4X4 programmer, and the DS1225 from Mouser, but before I pull out my original NVRAM still need the machined 28-DIP socket which I had to reorder as I messed up the PN, and also ordered a FW16W08 FRAM to play with and an Aries SOIC to DIP converter board.

After getting the cal data rewritten on a fresh D1225 I am assuming I will have to tackle the power supply caps next. Sometimes see a very small almost unnoticeable horizontal jitter on a displayed waveform, so this is probably ripple in one or more power supplies. I last time the scope was open also took a glance into the power supply board and noticed I do have the infamous RIFA exploding caps and at least the one that sits closer to the angle I was able to peer onto the board shows the typical small cracks. I'm on 120V so I understand the risk of them exploding is less than on 220v mains, but I will replace them asap once I have all the other PS caps on hand as well. Already have the replacements for those, but since pulling out the PS boards as a pair its not exactly easy, will probably wait until I have all the required elco caps on hand as well and get it done once.

BTW can someone please explain how does one take the power supply ripple reading for 120Hz only, as opposed to the total ripple reading? By using the HF reject triggering option?

Thanks.


tekscopegroup@...
 

Link above is only for one picture. Full album is really here:

https://groups.io/g/TekScopes/album?id=76874&p=Name,,,20,1,0,0

tekscopegroup@...
 

Added 4 pictures to my photo album showing rise time measurements of the 2465B (o.57nS) and also my 2247A (~2.0nS). BTW the 0.57nS rise time was confirmed with the corresponding parametric measurement, the result was exactly 0.57nS as well. Also included a close up of the 2N2369A avalanche pulse generator I build (last picture), and that requires around 90V to work, but I just use my Heathkit IG-4505 with DC output set to the 100V scale, and it works just fine. Much easier that having to build that cumbersome DC-DC converter used in the original pulser article.

https://groups.io/g/TekScopes/photo/76874/1?p=Name,,,20,1,0,0

BTW is it possible to reorder the pictures? I could not find a way to do it through the web interface.

tekscopegroup@...
 

On Tue, Nov 6, 2018 at 08:03 AM, Chuck Harris wrote:
Hey! Don't muck with the DAC adjustment, unless you are prepared
to do a full calibration!

It is not supposed to be +1.25 and -1.25 volts, but rather a 2.500V span.

Sure, if you are a perfectionist, and diddle with the 10K reference
resistor values, and put in perfect opamps, it can achieve those values,
but that is not a necessary goal: 2.500V span when doing the calibration
routine is the necessary goal. -1.25 and +1.36V references that are *stable*
is the goal, as any errors in them get stored in the calibration constants,
and as such calibrated out, when the scope is calibrated.

Any tweaking, or replacement of DAC parts that you do will require a
full calibration of your scope. Why? Because you have no idea what they
were like when it was last calibrated.

If they were on the low (or high) side of spec when last calibrated, and
you adjust them to be right on, with a DVM that was on the high (low) side
of spec), they errors could add up to be wrong enough to perform poorly.

-Chuck Harris
OK understood. I have not touched the adjustment at R2010. Only replaced both 10K 0.1% resistors (the original ones where both open). Also replaced R2016 1K 1% because I pulled it out by mistake and one of the contacts looked a bit iffy, so that one was also needing replacement anyway. The original value of this last resistor checked on my HP3478A was 1.00248K and the substitute measured 1.00302K, so only a 0.0539% difference between them. The voltages from the +1.36 and -1.25 references did not vary very much from what the where while still using the temporary 5% resistors. I initially had +1.3848 and now it is 1.3836v. And -1.2688 went to -1.2681v. Not much of a difference.

I was looking at the procedure to check the 2.5V DAC voltage span in the service manual (page 5-3) and plan on verifying it at pin 13 of J119. But I will not be making any adjustments to it, since as explained above this might actually be detrimental and worsen the calibration state of the scope. So for now I will only record the voltage range, and they will stay as is.

I have received my new GQ-4X4 programmer, and the DS1225 from Mouser, but before I pull out my original NVRAM still need the machined 28-DIP socket which I had to reorder as I messed up the PN, and also ordered a FW16W08 FRAM to play with and an Aries SOIC to DIP converter board.

After getting the cal data rewritten on a fresh D1225 I am assuming I will have to tackle the power supply caps next. Sometimes see a very small almost unnoticeable horizontal jitter on a displayed waveform, so this is probably ripple in one or more power supplies. I last time the scope was open also took a glance into the power supply board and noticed I do have the infamous RIFA exploding caps and at least the one that sits closer to the angle I was able to peer onto the board shows the typical small cracks. I'm on 120V so I understand the risk of them exploding is less than on 220v mains, but I will replace them asap once I have all the other PS caps on hand as well. Already have the replacements for those, but since pulling out the PS boards as a pair its not exactly easy, will probably wait until I have all the required elco caps on hand as well and get it done once.

BTW can someone please explain how does one take the power supply ripple reading for 120Hz only, as opposed to the total ripple reading? By using the HF reject triggering option?

Thanks.

Chuck Harris
 

Noise is endemic in electronics. It is related to the
temperature. The resistors, transistors, etc.. All make
a contribution to the noise.

The noise of a receiver is set by the noise of the front
end of the receiver. Once established, any further
amplification simply amplifies the noise... the signal to
noise ratio stays basically the same.... well, until overload.

When you have the scope in the higher gain positions, the
noise is being amplified, and is displayed as more fuzz.

Noise of this sort is called white noise. Its distribution
is fairly uniform across the frequency band of the scope.

If you run the scope at its full 350MHz bandwidth, it is
slurping in all of the front end's noise from DC to 350MHz,
and adding it to the trace, everywhere...

If you reduce the bandwidth of the scope, to say: 20MHz, there
is less overall noise to add into the trace, because there is
less overall bandwidth... the noise from 20MHz through 350MHz is
mostly blocked.

About the blink: Sorry, it has always been there with the
2465A and B models. It is not as apparent with the plain
model, mostly because the LED's are dimmer.

Wnen the LED's registers are loaded with the state of the
LED's on the panel, they all go into an LED ON state for
the duration of the load. It is a feature of the register
used.

CAL 05 is the routine that can read/set/reset the counters.
Its default position is to reset the counters. You can
set them to whatever you want... the technique requires
you to select the increment using the X10 button, and to
rotate the Delta Ref, and the Delta controls to make the
appropriate counter change... I know of nobody that does
this.

There is no specific manual for this option, but rather
there is the main instrument manual, and the GPIB options
manual.

GPIB on the 2465B is a complete waste for the usual user.
It only allows you to set the front panel controls, and
display some text on the screen. It does *not* allow you
to read anything that is derived from the CH1-4 inputs.

It's purpose is for use with the rack panel version of the
scope, when using the scope to do mindless calibration
and repair routines of military equipment. Basically, it
replaces the calibration manual with a computer as the
source of calibration information.

-Chuck Harris

tekscopegroup@... wrote:

Chuck as usual your explanations are outstanding. After reading them, just a few short extra questions/comments, bellow.

On Wed, Oct 31, 2018 at 09:49 PM, Chuck Harris wrote:
The design of the front panel is such that all of
the displays states are in registers that get strobed
whenever anything is changed on the front panel. That
shows up as a brief flash of all lights.

The 2465B uses 74F logic for those registers, the older
2465 used 74LS logic, and fairly dim LED's. The blink
is scarcely noticeable with the older 2465. The 2465B
uses much brighter LED's, and the blink is quite apparent.
I assumed that it was normal, but I was surprised to see the effect as it was never evident on any of the videos I'd seen before.

With 350MHz bandwidth comes a lot of ambient noise. Cut
the bandwidth, and you will cut the noise. That is why
the scope has the 20MHz bandwidth limit switch on the
front panel.
So it is normal to see some fuzziness on the traces at full bandwidth? I really have to go through this again, as I seem to remember the amount of fuzziness varied somewhat depending on the time/div setting, not sure that would be normal. I am still awaiting for the Mouser parts for the A5 board to arrive, and will confirm that once I have to put the scope back on the bench to work on replacing those parts.

The 2465B is not a frequency counter, and the A5 board's
10MHz reference has nothing to do with sweep or frequency
accuracy.

The way the 2465 family creates its sweep is by using a
miller integrator, and precision integration capacitors.
...snip...

Very nice explanation of the principle used to make the measurements, now I have much better understanding of the process.

It is standard practice of most sellers to remove all
calibration stickers, and stickers showing previous
ownership before the sale. Although I don't sell a lot
of scopes, when I do, I blow out the dust from the inside,
clean the outside, and the CRT, make any repairs, and
calibrate the scope, complete with zeroing the counters.
If I may ask, how do those hour and power cycle counters get zeroed out? I don't think I have seen the reset procedure explained in the service manual.

According to Manuel Maseda, Option 46 is the military
version of the scope (OS-288/G) that includes option 10
(IEEE-488), and 2 probes.
Is there a more specific service manual for this variant I should look for?
If you happen to know, are there any differences in the military version from the regular version?
Perhaps a sturdier build? or what where the military requirements?

Thanks again Chuck.

Alex



Chuck Harris
 

Hey! Don't muck with the DAC adjustment, unless you are prepared
to do a full calibration!

It is not supposed to be +1.25 and -1.25 volts, but rather a 2.500V span.

Sure, if you are a perfectionist, and diddle with the 10K reference
resistor values, and put in perfect opamps, it can achieve those values,
but that is not a necessary goal: 2.500V span when doing the calibration
routine is the necessary goal. -1.25 and +1.36V references that are *stable*
is the goal, as any errors in them get stored in the calibration constants,
and as such calibrated out, when the scope is calibrated.

Any tweaking, or replacement of DAC parts that you do will require a
full calibration of your scope. Why? Because you have no idea what they
were like when it was last calibrated.

If they were on the low (or high) side of spec when last calibrated, and
you adjust them to be right on, with a DVM that was on the high (low) side
of spec), they errors could add up to be wrong enough to perform poorly.

-Chuck Harris

tekscopegroup@... wrote:

Hi Tom, thanks very much for your input. Bellow just a quick follow up.

On Wed, Oct 31, 2018 at 04:08 PM, Tom Gardner wrote:
Highly unlikely the 10MHz is incorrect - but you can always measure it on your
other scope :)
Is there a test point designated on A5 to check on the 10MHz oscillator?
Just for fun and while I am at A5, might as well check that, although after reading Chuck's detailed explanation on how the scope actually performs the frequency measurements, the 10MHz is not used in the process, and I suspect that it will be within spec.

What's more likely is that the A5 voltages and/or calibration values are
invalid. Before tweaking anything, make sure the reference and DAC output
voltages are as specified in the service manual.
Yes, at the time of making those measurements both the positive and negative voltage reference values where/are still off. Did not want to touch the adjustment until the two 10.0K 0.1% resistors that where damaged by the leaking caps are replaced with the correct parts. They should arrive sometime this week, and once they are in, I will tweak R2010 to set the reference voltages to +1.36v and -1.25v.

Thanks again.

Alex

Dan Rae
 

On 11/6/2018 4:05 AM, toby@... wrote:
On 2018-11-06 7:36 a.m., tekscopegroup@... wrote:

Yes, I think Chuck (or someone else) pointed this out earlier in the
thread. The wider bandwidth the more noise in the trace, this is normal
on any scope afaik.
Particularly if you live in an area with nearby FM broadcast transmitters, the average scope probe will pick those up quite well :^)
dr

toby@...
 

On 2018-11-06 7:36 a.m., tekscopegroup@... wrote:
...
So it is normal to see some fuzziness on the traces at full bandwidth? I really have to go through this again, as I seem to remember the amount of fuzziness varied somewhat depending on the time/div setting, not sure that would be normal. I am still awaiting for the Mouser parts for the A5 board to arrive, and will confirm that once I have to put the scope back on the bench to work on replacing those parts.
Yes, I think Chuck (or someone else) pointed this out earlier in the
thread. The wider bandwidth the more noise in the trace, this is normal
on any scope afaik.

--Toby


...
Alex



tekscopegroup@...
 

On Thu, Nov 1, 2018 at 01:30 AM, Manuel Maseda wrote:


Alex,

If the scope has the optional CTT board then it is very simple with your
serial number scope to enable the external frequency input option (1E) by
simply moving the coax cable for rear BNC jack labeled Probe Out over 1
position on the CTT board connector.

Manuel
Hi Manuel,

Unfortunately my scope does not include the CT option. Also owning a 2247A, and routinely using the build-in counter timer, the CT variant was something that was desirable and high on my 2465 wish list, but ultimately when the right scope came along it was a straight B version only and I did not have much of a choice anymore. The only option included is 49, which as you and Chuck have pointed out means it is a military version. But as Chuck also very eloquently explained, the accuracy of the 10MHz internal oscillator does not play any role in the process of measuring frequency of a waveform (at least not without a CT option), so adding an external ref input is now a moot point.

Thanks for the input.
Alex

tekscopegroup@...
 

Hi Tom, thanks very much for your input. Bellow just a quick follow up.

On Wed, Oct 31, 2018 at 04:08 PM, Tom Gardner wrote:
Highly unlikely the 10MHz is incorrect - but you can always measure it on your
other scope :)
Is there a test point designated on A5 to check on the 10MHz oscillator?
Just for fun and while I am at A5, might as well check that, although after reading Chuck's detailed explanation on how the scope actually performs the frequency measurements, the 10MHz is not used in the process, and I suspect that it will be within spec.

What's more likely is that the A5 voltages and/or calibration values are
invalid. Before tweaking anything, make sure the reference and DAC output
voltages are as specified in the service manual.
Yes, at the time of making those measurements both the positive and negative voltage reference values where/are still off. Did not want to touch the adjustment until the two 10.0K 0.1% resistors that where damaged by the leaking caps are replaced with the correct parts. They should arrive sometime this week, and once they are in, I will tweak R2010 to set the reference voltages to +1.36v and -1.25v.

Thanks again.

Alex

tekscopegroup@...
 

Chuck as usual your explanations are outstanding. After reading them, just a few short extra questions/comments, bellow.

On Wed, Oct 31, 2018 at 09:49 PM, Chuck Harris wrote:
The design of the front panel is such that all of
the displays states are in registers that get strobed
whenever anything is changed on the front panel. That
shows up as a brief flash of all lights.

The 2465B uses 74F logic for those registers, the older
2465 used 74LS logic, and fairly dim LED's. The blink
is scarcely noticeable with the older 2465. The 2465B
uses much brighter LED's, and the blink is quite apparent.
I assumed that it was normal, but I was surprised to see the effect as it was never evident on any of the videos I'd seen before.

With 350MHz bandwidth comes a lot of ambient noise. Cut
the bandwidth, and you will cut the noise. That is why
the scope has the 20MHz bandwidth limit switch on the
front panel.
So it is normal to see some fuzziness on the traces at full bandwidth? I really have to go through this again, as I seem to remember the amount of fuzziness varied somewhat depending on the time/div setting, not sure that would be normal. I am still awaiting for the Mouser parts for the A5 board to arrive, and will confirm that once I have to put the scope back on the bench to work on replacing those parts.

The 2465B is not a frequency counter, and the A5 board's
10MHz reference has nothing to do with sweep or frequency
accuracy.

The way the 2465 family creates its sweep is by using a
miller integrator, and precision integration capacitors.
...snip...

Very nice explanation of the principle used to make the measurements, now I have much better understanding of the process.

It is standard practice of most sellers to remove all
calibration stickers, and stickers showing previous
ownership before the sale. Although I don't sell a lot
of scopes, when I do, I blow out the dust from the inside,
clean the outside, and the CRT, make any repairs, and
calibrate the scope, complete with zeroing the counters.
If I may ask, how do those hour and power cycle counters get zeroed out? I don't think I have seen the reset procedure explained in the service manual.

According to Manuel Maseda, Option 46 is the military
version of the scope (OS-288/G) that includes option 10
(IEEE-488), and 2 probes.
Is there a more specific service manual for this variant I should look for?
If you happen to know, are there any differences in the military version from the regular version?
Perhaps a sturdier build? or what where the military requirements?

Thanks again Chuck.

Alex

 

Alex,

Correction: the BNC jack is labled Word Recog Out.

Manuel

 

Alex,

If the scope has the optional CTT board then it is very simple with your serial number scope to enable the external frequency input option (1E) by simply moving the coax cable for rear BNC jack labeled Probe Out over 1 position on the CTT board connector.

Manuel

Chuck Harris
 

Hi Alex,

The design of the front panel is such that all of
the displays states are in registers that get strobed
whenever anything is changed on the front panel. That
shows up as a brief flash of all lights.

The 2465B uses 74F logic for those registers, the older
2465 used 74LS logic, and fairly dim LED's. The blink
is scarcely noticeable with the older 2465. The 2465B
uses much brighter LED's, and the blink is quite apparent.

With 350MHz bandwidth comes a lot of ambient noise. Cut
the bandwidth, and you will cut the noise. That is why
the scope has the 20MHz bandwidth limit switch on the
front panel.

Working amounts of power supply ripple are not generally
noticeable. Large amounts, usually cause erratic operation.
An example of erratic operation would be trigger jitter.

The 2465B is not a frequency counter, and the A5 board's
10MHz reference has nothing to do with sweep or frequency
accuracy.

The way the 2465 family creates its sweep is by using a
miller integrator, and precision integration capacitors.

The way it measures frequency is rather convoluted, but
depends entirely on the sweep accuracy.

Think of it this way, the sweep is generated by charging
a capacitor with a constant current. It is correlated
to both the graticules, and the cursors during calibration.

The frequency measuring method uses the trigger hybrid
and a DAC to measure the zero crossing points of the
waveform, and uses the delay sweep to measure the time
between the zero crossing points. The CPU then performs
the inversion, and the display shows that number as the
frequency. It is not a frequency counter!

It is standard practice of most sellers to remove all
calibration stickers, and stickers showing previous
ownership before the sale. Although I don't sell a lot
of scopes, when I do, I blow out the dust from the inside,
clean the outside, and the CRT, make any repairs, and
calibrate the scope, complete with zeroing the counters.

It would look as you are describing your scope, regardless
of how old it really is. If I cannot repair it, and clean
it up to that degree, it becomes a parts source.

According to Manuel Maseda, Option 46 is the military
version of the scope (OS-288/G) that includes option 10
(IEEE-488), and 2 probes.

-Chuck

tekscopegroup@... wrote:

On Tue, Oct 30, 2018 at 01:11 PM, Chuck Harris wrote:

For what it's worth, the power cycle counter, and on time counter
are meant to be reset after every calibration. They are there to
let the technician know how long it has really been since the last
calibration... as opposed to whatever the customer says..

They don't mean much to a customer. If you see really low numbers,
it simply means the scope saw little use since its last calibration.

-Chuck Harris
Hi Chuck, this certainly makes a lot of sense. Thanks for clarifying it, never heard this simple and logical explanation from anyone else, other that people being very happy when they see low numbers on those counters on a newly acquired scope. This one does not have any past cal stickers at all, so wonder if it ever was calibrated after being purchased.

Since I am new to this model, I noticed that when pressing any front panel switch, all the other indicators seem to very briefly flash in unison before the requested change is executed. Is this normal? Also, under certain conditions, specially when using the x10 horizontal magnifier and on the lower vertical v/div ranges (10mV and bellow), the traces seem somewhat blurry. But without changing the v/div range they clear up nicely and look very sharp when I engage the 20MHz BW limit, tough. Would this possibly mean HF power supply noise or power line ripple creeping into the circuits? (aging filter caps that need to be replaced?). I have not yet gotten to checking all the power rails at J119, will do so when the Mouser parts order arrives and the cover needs to come off again.

The other issue I've seen is that the automatic frequency measurement (press the measure button and then select 1 for frequency) is off usually by at least 10% or so, sometimes even more. Accuracy of the internal 10MHz reference oscillator not really being that accurate? If so wish there was a way to retrofit an external 10MHz ref input, which I understand is one of the standard options. I read somewhere that it is fairly easy to do it, but found no detailed information. As a comparison, my 2247A will always read the frequency very accurately, and its off by just 71Hz tested against a freshly calibrated rubidium oscillator.

Lastly, I figure you're probably the best person to ask this. On the installed options sticker on the back, the only field marked (punched out) is 46 (between the 22 and 1E fields) on this rear aluminum sticker. So far I have not been able to find any reference at all for an Option 46 on these scopes, and nobody that I asked so far seems to know. Are you by any chance familiarized with what this option 46 entails?

Thanks much.
-Alex



Tom Gardner
 

On 31/10/18 21:48, tekscopegroup@... wrote:
On Tue, Oct 30, 2018 at 01:11 PM, Chuck Harris wrote:
For what it's worth, the power cycle counter, and on time counter
are meant to be reset after every calibration. They are there to
let the technician know how long it has really been since the last
calibration... as opposed to whatever the customer says..

They don't mean much to a customer. If you see really low numbers,
it simply means the scope saw little use since its last calibration.

-Chuck Harris
Hi Chuck, this certainly makes a lot of sense. Thanks for clarifying it, never heard this simple and logical explanation from anyone else, other that people being very happy when they see low numbers on those counters on a newly acquired scope. This one does not have any past cal stickers at all, so wonder if it ever was calibrated after being purchased.

Since I am new to this model, I noticed that when pressing any front panel switch, all the other indicators seem to very briefly flash in unison before the requested change is executed. Is this normal?
Yes. IIRC all the indicators are driven by a shift register; one changes and all stages of the shift register have to be loaded serially.

Also, under certain conditions, specially when using the x10 horizontal magnifier and on the lower vertical v/div ranges (10mV and bellow), the traces seem somewhat blurry. But without changing the v/div range they clear up nicely and look very sharp when I engage the 20MHz BW limit, tough. Would this possibly mean HF power supply noise or power line ripple creeping into the circuits? (aging filter caps that need to be replaced?). I have not yet gotten to checking all the power rails at J119, will do so when the Mouser parts order arrives and the cover needs to come off again.
Measure the ripple and replace the capacitors where beneficial. Replace them one at a time; in some manuals two caps are swapped compared to the actual boards. That is well documented elsewhere.

Don't forget that there is a lot more thermal noise in a 350MHz bandwidth than a 20MHz bandwidth - you may simply be seeing that thermal noise.


The other issue I've seen is that the automatic frequency measurement (press the measure button and then select 1 for frequency) is off usually by at least 10% or so, sometimes even more. Accuracy of the internal 10MHz reference oscillator not really being that accurate? If so wish there was a way to retrofit an external 10MHz ref input, which I understand is one of the standard options. I read somewhere that it is fairly easy to do it, but found no detailed information. As a comparison, my 2247A will always read the frequency very accurately, and its off by just 71Hz tested against a freshly calibrated rubidium oscillator.
Highly unlikely the 10MHz is incorrect - but you can always measure it on your other scope :)

What's more likely is that the A5 voltages and/or calibration values are invalid. Before tweaking anything, make sure the reference and DAC output voltages are as specified in the service manual.

tekscopegroup@...
 

On Tue, Oct 30, 2018 at 01:11 PM, Chuck Harris wrote:

For what it's worth, the power cycle counter, and on time counter
are meant to be reset after every calibration. They are there to
let the technician know how long it has really been since the last
calibration... as opposed to whatever the customer says..

They don't mean much to a customer. If you see really low numbers,
it simply means the scope saw little use since its last calibration.

-Chuck Harris
Hi Chuck, this certainly makes a lot of sense. Thanks for clarifying it, never heard this simple and logical explanation from anyone else, other that people being very happy when they see low numbers on those counters on a newly acquired scope. This one does not have any past cal stickers at all, so wonder if it ever was calibrated after being purchased.

Since I am new to this model, I noticed that when pressing any front panel switch, all the other indicators seem to very briefly flash in unison before the requested change is executed. Is this normal? Also, under certain conditions, specially when using the x10 horizontal magnifier and on the lower vertical v/div ranges (10mV and bellow), the traces seem somewhat blurry. But without changing the v/div range they clear up nicely and look very sharp when I engage the 20MHz BW limit, tough. Would this possibly mean HF power supply noise or power line ripple creeping into the circuits? (aging filter caps that need to be replaced?). I have not yet gotten to checking all the power rails at J119, will do so when the Mouser parts order arrives and the cover needs to come off again.

The other issue I've seen is that the automatic frequency measurement (press the measure button and then select 1 for frequency) is off usually by at least 10% or so, sometimes even more. Accuracy of the internal 10MHz reference oscillator not really being that accurate? If so wish there was a way to retrofit an external 10MHz ref input, which I understand is one of the standard options. I read somewhere that it is fairly easy to do it, but found no detailed information. As a comparison, my 2247A will always read the frequency very accurately, and its off by just 71Hz tested against a freshly calibrated rubidium oscillator.

Lastly, I figure you're probably the best person to ask this. On the installed options sticker on the back, the only field marked (punched out) is 46 (between the 22 and 1E fields) on this rear aluminum sticker. So far I have not been able to find any reference at all for an Option 46 on these scopes, and nobody that I asked so far seems to know. Are you by any chance familiarized with what this option 46 entails?

Thanks much.
-Alex

Chuck Harris
 

For what it's worth, the power cycle counter, and on time counter
are meant to be reset after every calibration. They are there to
let the technician know how long it has really been since the last
calibration... as opposed to whatever the customer says..

They don't mean much to a customer. If you see really low numbers,
it simply means the scope saw little use since its last calibration.

-Chuck Harris

tekscopegroup@... wrote:
... EXER 05 indicates this scope has only seen 360 hours of On time, and 125 power
cycles (those last 25 are probably mine). From the writings and labels on the front
cover and one side of the scope it looks like this was a designated field instrument
that probably did not go out that much. The insides are pristine, and cosmetically
the outside and front panel controls are in very good shape. Maybe the A/B timebase
Sec/Div concentric knobs feel a bit wiggly, maybe a nut or something will have to be
tightened inside? I am also glad the so very important front panel cover was
included, and the always good to have pouch. No probes unfortunately.


Once the parts order arrives, and I get a chance to throw them on the board, will update this thread again.
Any comments/suggestions always appreciated.

Alex