Date   
Re: Repairability of SD-24, SD-30 & SD-32 sampling heads

Dave Brown
 

Far as I know he still works at a university in Portugal -he's been there for some years and is well known in scientific and amateur (especially EME) circles.
73
Dave, ZL3FJ

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Bob Koller via Groups.Io
Sent: Tuesday, March 26, 2019 13:05
To: TekScopes@groups.io
Subject: Re: [TekScopes] Repairability of SD-24, SD-30 & SD-32 sampling heads

Yes, Luis has done great work! He is in South America I think. Ascertaining and sourcing the correct parts can be difficult.

Re: 11801 is reassembled, up and running :-)

 

On Mon, Mar 25, 2019 at 10:52 PM, Reginald Beardsley wrote:

I tried to copy the A5-U300 ROM but I'm not sure that succeeded. The TNM5000
said it failed to identify it. Can anyone tell me what type of EPROMs are used
in the scope?
27C010 and 27C512

/Håkan

Re: 11801 is reassembled, up and running :-)

 

On Tue, Mar 26, 2019 at 10:49 AM, zenith5106 wrote:



I tried to copy the A5-U300 ROM but I'm not sure that succeeded. The
TNM5000
said it failed to identify it. Can anyone tell me what type of EPROMs are
used
in the scope?
27C010 and 27C512
I may have to take part of that back.
In my F/W EPROM collection I don't have 11801 but there is a note saying that 11801 can also use 11801A F/W
which I have and it uses both types. I now begin to think that is wrong and if so 11801, just like 11802 no letter,
use only 27C512.

/Håkan

Re: 11801 is reassembled, up and running :-)

Reginald Beardsley
 

Thanks. It will be a while before I take it apart again, but I'll make a note in my service manual.

Fortunately, most of my HP gear lists the parts in the manuals, so those will be easier to do.

I've attached a photo showing the calibrator output trace. The measured rise time is shown in the lower left at 32 ps. I've got smoothing on.



--------------------------------------------

On Tue, 3/26/19, zenith5106 <hahi@...> wrote:

Subject: Re: [TekScopes] 11801 is reassembled, up and running :-)
To: TekScopes@groups.io
Date: Tuesday, March 26, 2019, 7:01 AM

On Tue, Mar 26, 2019 at 10:49 AM,
zenith5106 wrote:

>
> >
> > I tried to
copy the A5-U300 ROM but I'm not sure that succeeded.
The
> > TNM5000
>
> said it failed to identify it. Can anyone tell me what
type of EPROMs are
> > used
> > in the scope?
>

> 27C010 and 27C512
>
I may have to take part of
that back.
In my F/W EPROM collection I
don't have 11801 but there is a note saying that 11801
can also use 11801A F/W
which I have and it
uses both types. I now begin to think that is wrong and if
so 11801, just like 11802 no letter,
use
only 27C512.

/Håkan

Re: Impedance matching question

David Berlind
 

That was a decent video, thank you. It doesn't seem like he had problems
with the terminators themselves. In fact, he uses them to address
mismatches. I'd be curious to know (from anyone who knows) why maximum
power (matched impedance) is ideal in some situations, but a low-Z to
high-Z arrangement is the ideal in other situations (ie: guitar to
amplifier or microphone to PA). I realize the outcome in the latter
situation; you preserve the audio highs and lows. But need some schooling
on why to maximize voltage at the load (vs. maximizing transfer power) in
those situations and why the mismatch isn't destructive to the signal. And
correspondingly, why the same isn't true of the impedance match between
output tubes and the primary of an output transformer since its a similar
audio application. Again, I understand the requirements and outcomes... but
am confused about the underlying physics.

Thanks in advance for this help.

On Mon, Mar 25, 2019 at 8:09 PM Roy Thistle <roy.thistle@...>
wrote:

Hi:
If you haven't watched EEVblog #652, he demonstrates a couple of problems
that can arise when using coax, terminators, and Ts, to connect a sig gen
to a scope.
Cheers.



Re: 11801 is reassembled, up and running :-)

Albert Otten
 

Attachments are not allowed here Reg. Via the website you can create a new Album in the Photos section and put your picture(s) there. If you do so, it's handy for "us" if you insert a link to the album in your messages.
Albert

On Tue, Mar 26, 2019 at 02:06 PM, Reginald Beardsley wrote:


I've attached a photo showing the calibrator output trace. The measured rise
time is shown in the lower left at 32 ps. I've got smoothing on.

Re: Impedance matching question

Craig Sawyers
 

That was a decent video, thank you. It doesn't seem like he had problems with the terminators
themselves. In fact, he uses them to address mismatches. I'd be curious to know (from anyone who
knows) why maximum power (matched impedance) is ideal in some situations, but a low-Z to high-Z
arrangement is the ideal in other situations (ie: guitar to amplifier or microphone to PA). I
realize the
outcome in the latter situation; you preserve the audio highs and lows. But need some schooling on
why to maximize voltage at the load (vs. maximizing transfer power) in those situations and why the
mismatch isn't destructive to the signal. And correspondingly, why the same isn't true of the
impedance match between output tubes and the primary of an output transformer since its a similar
audio application. Again, I understand the requirements and outcomes... but am confused about the
underlying physics.
It is to do with the frequency range. As soon as the length of the cable becomes a significant
fraction of the electrical wavelength in the cable, you need to impedance match. That is because
energy is reflected at an impedance discontinuity, so you end up with standing waves along the length
of the cable. For a 1 metre long coax the wavelength becomes a significant fraction of the cable
length by about 10MHz, so you need to impedance match.

With audio, the wavelength is so long (at 20kHz it is about 10km in a typical coax cable) you
absolutely do not need to match. Hence you guitar example.

Going way back long distance telegraph and telephone lines were significant fractions of an audio
wavelength in the cables, and they needed to impedance match.

Craig

Re: 11801 is reassembled, up and running :-)

Bob Koller
 

They must have changed the cal output circuitry on the later models.

Re: Impedance matching question

David Berlind
 

Thanks Craig... so, if I were to summarize what you wrote, at such short
distances, there's really no opportunity for a reflected signal to go out
of phase with the incident signal?

In watching the EEVblog videos, he's clearly using pretty high frequencies
(well out of the audio spectrum). So, your explanation is consistent with
that.

So, two questions remain.

1. why is an impedance match between output tubes and the output
transformer primary so important given the short physical differences. Or,
maybe the tube specs are not showing the actual impedance, but rather the
recommend Hi-Z on the load end to offer the optimal Low-Z to Hi-Z ratio?

2. Why is a Low-Z to Hi-Z ratio desired in audio applications vs. an
impedance match? I understand your point that it doesn't matter at low
distances, but Low-Z to Hi-Z appears to be an objective (iow, the objective
is to avoid a match, by orders of magnitude). Does the higher resultant
voltage (amplitude) at the load spread the signal out in a way that give
the amp more to work with from a fidelity POV?

On Tue, Mar 26, 2019 at 9:59 AM Craig Sawyers <c.sawyers@...>
wrote:

That was a decent video, thank you. It doesn't seem like he had problems
with the terminators
themselves. In fact, he uses them to address mismatches. I'd be curious
to know (from anyone who
knows) why maximum power (matched impedance) is ideal in some
situations, but a low-Z to high-Z
arrangement is the ideal in other situations (ie: guitar to amplifier or
microphone to PA). I
realize the
outcome in the latter situation; you preserve the audio highs and lows.
But need some schooling on
why to maximize voltage at the load (vs. maximizing transfer power) in
those situations and why the
mismatch isn't destructive to the signal. And correspondingly, why the
same isn't true of the
impedance match between output tubes and the primary of an output
transformer since its a similar
audio application. Again, I understand the requirements and outcomes...
but am confused about the
underlying physics.
It is to do with the frequency range. As soon as the length of the cable
becomes a significant
fraction of the electrical wavelength in the cable, you need to impedance
match. That is because
energy is reflected at an impedance discontinuity, so you end up with
standing waves along the length
of the cable. For a 1 metre long coax the wavelength becomes a significant
fraction of the cable
length by about 10MHz, so you need to impedance match.

With audio, the wavelength is so long (at 20kHz it is about 10km in a
typical coax cable) you
absolutely do not need to match. Hence you guitar example.

Going way back long distance telegraph and telephone lines were
significant fractions of an audio
wavelength in the cables, and they needed to impedance match.

Craig





Re: 11801 is reassembled, up and running :-)

Reginald Beardsley
 

The user manual I quoted has a revision date of May 1989. The August 1988 service manual states the calibrator is < 35 ps. The February 1989 revision page states the same rise time.

As I noted previously. I also got a 300 ps rise time from the calibrator due to something not being set properly. This persisted when I used autoset, but eventually went away after I power cycled it a couple of times and used the autoset again. The behavior suggested an off by 10x error in the timebase generator strobe line. But I have far too little experience with the instrument to be sure of anything.

Re: Impedance matching question

Dale H. Cook
 

At 09:58 AM 3/26/2019, Craig Sawyers wrote:

Going way back long distance telegraph and telephone lines were significant fractions of an audio wavelength in the cables, and they needed to impedance match.
Through the tube era and the discrete solid state era professional balanced audio lines in radio and recording studios were also impedance matched at 600 ohms (earlier 500 ohms) because they were transformer coupled and power sourced. The constant impedance was implemented for maximum power transfer. It was not until the advent of high quality op amps that voltage sourced balanced audio lines became the norm in studios.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html

Re: 11801 is reassembled, up and running :-)

Albert Otten
 

On Tue, Mar 26, 2019 at 03:28 PM, Reginald Beardsley wrote:


The user manual I quoted has a revision date of May 1989. The August 1988
service manual states the calibrator is < 35 ps. The February 1989 revision
page states the same rise time.

As I noted previously. I also got a 300 ps rise time from the calibrator due
to something not being set properly. This persisted when I used autoset, but
eventually went away after I power cycled it a couple of times and used the
autoset again. The behavior suggested an off by 10x error in the timebase
generator strobe line. But I have far too little experience with the
instrument to be sure of anything.


Re: Impedance matching question

Craig Sawyers
 

1. why is an impedance match between output tubes and the output transformer primary so
important given the short physical differences. Or, maybe the tube specs are not showing the actual
impedance, but rather the recommend Hi-Z on the load end to offer the optimal Low-Z to Hi-Z ratio?
Because there is a mismatch between the high plate resistance of the output pentodes or tetrodes
(about 4.5k-ohms in push pull) and the loudspeaker. The impedance transformation goes as the square
root of the turns ratio. So to match 4.5kk to 8 ohms needs a turns ratio of root(4500/8) = 24:1 turns
ratio. To deliver 30W into 8 ohms (typical for 6550's in push pull) needs 21V peak, times 24 = 500V.
The anode/plate voltage will be 560V - which is consistent with a 500V signal peak.

The details are of course more complicated than that - so you'll just have to read around.

2. Why is a Low-Z to Hi-Z ratio desired in audio applications vs. an impedance match?
Because if you do an impedance match at audio you lose half the signal. So your signal to noise ratio
goes down by 6dB. Which is why no-one does it - there is absolutely no upside.

We're kind of off-topic here. If you want to discuss audio, try
https://www.diyaudio.com/forums/index.php or https://www.stevehoffman.tv/ . There are lots more out
there.

Craig

Re: Repairability of SD-24, SD-30 & SD-32 sampling heads

Egge Siert
 

Hi Reginald,

It is in the archives:

https://groups.io/g/TekScopes/topic/7659008#141241

Enjoy.

Egge Siert

Switching power supplies

Brendan
 

I have a few questions about power supplies and would like some opinions. Are switching powers supplies inherently harder on components than linear power supplies? If you picked up a 70's-80's vintage scope with a SMPS would you replace power supply components before using it as a daily driver? Or do you treat all power supplies the same and visually inspect, check for ripple and call it good? From my reading it seems that when a SMPS melts down the chain reaction damage has the possibility of being bad.


Brendan

Re: Switching power supplies

Chuck Harris
 

Tough question.

Yes, switching supplies are inherently harder on
components than linear, but they also use much better
parts. And they are more likely to be designed using
math, rather than rules of thumb. And they are more
likely to have extensive protection devices to prevent
catastrophic failures from occurring.

Linear supplies are heavy, are more likely to break your
toes, and make copious amounts of heat. That heat soaks
into everything around them, and causes component failure.

Tektronix used some really uber parts in their 70's vintage
supplies. In some cases, I cannot find modern parts that
were as good as what they used.

I would take it through calibration, testing the ripple
and voltages, and just use it. If it fails, fix the failure.

Odds are very, very, good that in prophylactically replacing
parts you are going to introduce failures, now and in the
future. Replacing a 10,000 hour rated part with a 1000 hour
part, isn't going to improve reliability.

-Chuck Harris

Brendan via Groups.Io wrote:

I have a few questions about power supplies and would like some opinions. Are switching powers supplies inherently harder on components than linear power supplies? If you picked up a 70's-80's vintage scope with a SMPS would you replace power supply components before using it as a daily driver? Or do you treat all power supplies the same and visually inspect, check for ripple and call it good? From my reading it seems that when a SMPS melts down the chain reaction damage has the possibility of being bad.


Brendan

Re: Switching power supplies

Tom Gardner
 

On 26/03/19 20:37, Brendan via Groups.Io wrote:
I have a few questions about power supplies and would like some opinions. Are switching powers supplies inherently harder on components than linear power supplies? If you picked up a 70's-80's vintage scope with a SMPS would you replace power supply components before using it as a daily driver? Or do you treat all power supplies the same and visually inspect, check for ripple and call it good? From my reading it seems that when a SMPS melts down the chain reaction damage has the possibility of being bad.
Replace Rifa mains interference suppression delayed action smoke generators on sight; if there is any sign of cracking in the transparent case, don't even turn it on.

Where there are tantalum beads that are operating near their rated voltage (e.g. a 15V tant on a 13V rail), replace those with a higher voltage.

Visually inspect, measure, replace if there's a problem.

Otherwise, if it ain't broke, don't fix it.

11801 calibrator rise time

Reginald Beardsley
 

I think I figured out why the calibrator rise time measurement doesn't read to spec. I warmed up the 11810 for about 40 minutes to do the Enhanced Accuracy adjustments. That seemed to go fine except afterwards when I measured the rise time I was getting >400 ps. The 11801 will remember the incorrect settings through a power cycle.

If you do the Loop Gain adjustment in the Enhanced Accuracy menu it resets something which results in incorrect values. If you go to the Utility menu and press Initialize you should now be able to set the Trigger to Internal, press Autoset, adjust the time base, turn on Hardware measurement and get <35 ps rise time.

Unfortunately, it does not appear to be possible to measure the rise time on more than one one channel.

I think a bunch of the Chinese DSO designers must have spent a lot of time using an 11801 and thought that was what a scope UI should look like. Even after reading all the way through the User manual the UI is still confusing because of the strange locations of various settings.

The tip off came from this line on p 82 of the User manual:

"Whenever you begin a new task using the 11801. you should initialize the system so that all the settings are at "factory default" . That way you do not get unexpected results because of settings remaining from the last use of the 11801."

BTW I have a 2 port divider feeding the upper channel of my SD-22s and the waveforms look to be exactly the same. The pieces of hardline from the divider to the heads are different lengths and I have not been able to shift one relative to the other to see how closely they overlay as there is a 340 ps delay between the two. The divider increases the rise time to 42 ps. It's an MBC Technology unit. No frequency rating specified.

I just discovered that it reset the time base readings when I removed the splitter and turned off one channel to take a look at how much of the 7% overshoot was the splitter which it turns out is about 5% of the total.

There's a little bit of ringing on the calibrator step at 12.2 GHz which is probably the result of reflections where the semi-rigid SMA cable connects to the 3.5 mm calibrator and sampling head connectors.

I am quite agog at how precise this thing is. Getting the full performance out of it will take some serious skill.

Re: Switching power supplies

Glenn Little
 

My take on this after replacing thousands of surface mount electrolytic capacitors is replace them all when you get a new to you device that is more than ten or so years old.

Switchers are harder on electrolytics because they run at a higher frequency than a linear supply and the bean counters usually required the least expensive part to be installed to get the instrument out of warranty.

My take on surface mounted electrolytics is that the fail for two reasons. The seal where the positive lead exits the case was violated during the reflow process. Or the capacitors was not properly selected for the task at hand.

When I replace power supply capacitors in switchers, I select the highest temperature capacitors available with the highest ripple current rating that will fit into the available space. I do not use 85 degree C capacitors unless they are all that is made in that value and voltage.

When doing repair work on cameras and tape decks in TV stations, I never saw a failure of a capacitor that I replaced with the above guidelines. I may have not waited long enough or may have been lucky.

Large computer grade electrolytics are the exception. Do not replace unless needed. These do not usually cause board damage that cannot be repaired.

See: https://www.eetimes.com/author.asp?section_id=183&doc_id=1279791#

Hope this helps.

Glenn

On 3/26/2019 4:37 PM, Brendan via Groups.Io wrote:
I have a few questions about power supplies and would like some opinions. Are switching powers supplies inherently harder on components than linear power supplies? If you picked up a 70's-80's vintage scope with a SMPS would you replace power supply components before using it as a daily driver? Or do you treat all power supplies the same and visually inspect, check for ripple and call it good? From my reading it seems that when a SMPS melts down the chain reaction damage has the possibility of being bad.


Brendan


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Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"

Re: Repairability of SD-24, SD-30 & SD-32 sampling heads

Jim Ford
 

Hmmm...  Did he die-bond, wire-bond, and package the FPGA or just solder it onto the board?  Not so impressive if it's the latter.  Still, the link to the website shows microwave devices being bonded in hybrid packages to repair mixers in spectrum analyzers - now that's impressive!Jim FordSent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Craig Sawyers <c.sawyers@...> Date: 3/25/19 5:07 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Repairability of SD-24, SD-30 & SD-32 sampling heads He clearly knows what he is doing. You don't knock up something with an Altera FPGA unless you have a major development lab at your disposal https://www.qsl.net/ct1dmk/gw_04.jpgCraig> -----Original Message-----> From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jose Luu> Sent: 25 March 2019 23:29> To: TekScopes@groups.io> Subject: Re: [TekScopes] Repairability of SD-24, SD-30 & SD-32 sampling heads>> https://www.qsl.net/ct1dmk/wbond_ex.html>> This guy seem to have made a home hybrid lab and repairs. Could former professionals comment ?>> Best> Jose>>> On Mon, Mar 25, 2019 at 9:30 PM Bob Koller via Groups.Io <testtech= yahoo.com@groups.io> wrote:>> > How well I know. My last job in the hybrid business was at Teledyne> > Microelectronics. Space Qual parts had reams of paperwork, x-rays,> > PIND test,photographs, etc...> > Tek, Keysight, and many other still , out of necessity, use hybrid> > technology with custom parts, in the front ends, and other places, of> > very high frequency instruments. But, commercial hybrid production> > has, I think, largely been supplanted by ASIC, FPGA, and more modern,> > more reliable, less expensive technology.> >> >> >> >>>