Date   

FS: Tektronix Scope-Mobile 200C

ppppenguin
 

For sale: Tektronix Scope-Mobile 200C . Suits many 400 series and 2xxx series instruments.

Good condition.

https://w140.com/tekwiki/images/e/ea/062-1533-04.pdf

Best collected but might be possible to dismantle and ship at cost. Location is London N12, UK.

Donation to BECG (registered charity) please: https://becg.org.uk/


Re: 2nd life for a 575 after resting for 30+ years in the attic #photo-notice

 

Hi Joe,

this tale reminds me of my 575, that was sitting together with a 576 for a number of years.... in an attic.

I took down the 576 and it behaved like the proverbial old lady... bad HV transformer, recently a bunch of bad transistors...

Eventually I took a look at the 575. Having the habit of first trying out what happens when rising the variac, thermal cam at hand, well... it worked flawlessly!! Did some realignment, not much was needed. It still has all its original caps, bumble bees, selenium stuff and whatnot that might fail one day. Now its sitting in a (dry) basement, on a shelf connected to the power line where I can switch it on from time to time. So fare no issues.

On the other hand, the old lady... the 576 is sitting on my bench now, in regular use, and the step generator begins acting up (again), doing steps only if well warmed up ;-)
Probably the IC that enables/disables the step counter has an issue...

cheers
Martin


Re: How to troubleshoot a faulty 7B92A?

Mark Vincent
 

Thierry,

I am glad you are making progress. The schematic shows that when the div. knob is pushed (usual operation), that grounds the 74112 through the 68 ohm resistor (R861) J & K inputs making the Q outputs static as you see. When it is pulled, the 74112 oscillates. The function table shows the states of the inputs and outputs. From the table, this IC appears to be working correct.

See if you have the 400mV pulses at the collector of Q358. This is waveform 7 on <3>. You can pull and reinsert the short coax between J260 and J270. The inner contact could be dirty. The trig. sens. pot may need to be adjusted. The TD bias pots may also need adjusting a bit. There should be a pulse at DA at ,5V d-c.

Now back to the other side of the plug-in on the interface board. Check the waveforms 1, 2, 3 and 5-11 on page <5>. See if you have them there. Also check the transistors there with the number mentioned earlier if you have not already done so. The leakage in these will be from collector to emitter as a diode check. An analogue meter will have the needle vertical on the Rx1 scale. Usually the same number that has a leakage of the 0367 in something, the others likely will be leaky as well. The manual will tell you the Q numbers.

Mark


OT: recommendation for a VGA and USB KVM switch?

Jim Ford
 

Hi, everybody.   At the risk of TMA (Too Many Acronyms), I ask for a recommendation for a reliable 2-port KVM switch that does VGA video and keyboard and mouse over USB. I've not had issues with the video, but the USB interface is a real PITA!  Just got a new work laptop computer, and I think that was the last straw for my existing Belkin KVM switch.  Now it doesn't work at all, after being flaky with the keyboard and/or mouse for many years.  Why is the USB part so hard to get right?!         TIA, Jim Ford Sent from my Verizon, Samsung Galaxy smartphone


Re: TEK 2215A info

Brian Cockburn
 

Thanks for the pictures of the various boards. Could we please have a picture of the back showing connectors and especially the label showing options (Like https://w140.com/tekwiki/wiki/465#/media/File:Tek-465-back.jpg or https://w140.com/tekwiki/wiki/File:Tek_2467_rear.jpg) ?


Re: 2nd life for a 575 after resting for 30+ years in the attic #photo-notice

 

My understanding of the paper tubes over the metal can capacitors is that this was done when the can was not at ground potential. The cardboard tube is meant to insulate the metal can, either to prevent shorting to nearby components, or to prevent people from touching the non-grounded cans and getting a shock.

-- Jeff Dutky


2nd life for a 575 after resting for 30+ years in the attic #photo-notice

Joe
 

Hi,
four months ago really by chance I was able to add a Tek 575 to my little collection. As it has got serial # 1818 it is a pretty early one and the cabinet has a definitely different texture than later instruments. It had been resting for more than 30 years now in an attic after serving a Siemens Munich lab engineer.
So I asked here and there for advice how to bring it back to life safely (so many thanks Dennis T. !) and I learned that my method to reform electrolytics - practised on many tube radios before - seemed to be more than rude. I promised to give it much more time!
Another thing that I learned is that selenium rectifiers do have a very limited life expectation, "the question is not if but when they will fail". So I decided to do the Mod M5272 to upgrade to silicon rectifiers first of all.
And well, recapping is a must. I selected all of the HV caps and these "bumble bee" called caps and some "Good-all" caps to be replaced. Most of them proved to be more or less leaky!
Today was the day: After several hours of gradually reforming electrolytics I dared to try if I could get a trace on the screen. Finally rising the variac to 90% of normal line voltage rewarded me not only with a bright and sharp trace but with a family of curves when a BF 259 transistor was to act as a guinea pig! I am happy now that I took the long way to save that instrument.
Now it is time for some tuning, checking the tubes (most of all original but some German "Siemens" tubes), cleaning the faceplate and doing longer tests before recalibration will be attempted.
I have just started a photo album "Tek 575". Again many thanks for all of the advice!

Joe


Re: How to explain how negative feedback lowers noise?

Mike Merigliano
 

What's wrong with mentioning the IEEE? I know a little bit about it (a good friend of mine is a past president, and we talk about it sometimes). Just curious, as a non-EE person.

This is already off-topic, so if the answer is long and complicated, there's not much sense in gumming things up further.

Thanks.

On 3/29/2021 10:34 AM, Roy Thistle wrote:
On Sun, Mar 28, 2021 at 04:12 PM, Jeff Dutky wrote:

The trouble with having all the world's knowledge at our fingertips is that so
much of what so many know is wrong.
There's all sorts of things problematic with that statement; but, there is... I would claim... a core of truth to it.
One consequence is that it takes more than an opinion... or more than an opinion and an advanced STEM degree to opine "truthfully" on the topics of, "Who discovered what," and "when and where it was discovered."
For instance, some once common tropes... now since revised... and being revised.
Robert Fulton didn't invent the steam engine... but, maybe the first steam powered boat?
Bell didn't invent the telephone.. but was the first to successfully patent it in the U.S?
Farnsworth didn't invent the television... but was maybe the first to display a transmitted image?
That is not to say all of these people were not very important contributors.
As for the "truth" of the genesis of of any particular invention... I'd say, leave discovering it to the professionals: they are sometimes found, hibernating under piles of dusty books, in a tiny closet of an office... sequestered off from the mostly un-traveled corridors of the department of Medieval Studies... or the like. Usually, such individuals have spent years, if not their whole career, trying to answer "who" invented some particular technology.
I know some people on this forum are incensed at the mention of the I.E.E.E. ;but, they do publish some well received monographs on topics concerning the history of science and technology.
Other literature is less accessible... and typically in journals, or university libraries.


Re: How to troubleshoot a faulty 7B92A?

Thierry Delaitre
 

Thanks Mark

an update

I have cleaned the time/div contacts.

I also verified S800 and S490 offline as well as using the scope.

AR only works when the time div knob is pulled.

When the time div knob is pushed
- AP remains low and BM remains high
- J & K of the 1st flip/flop are high and the flip/flop is meant to operate in toggle mode according to the 74LS112 data sheet
- the clock continues to operate at the input of the flip/flop
- is it expected that AP remains low and BM remains high ?

There is a nice sweep at TP450 and no sweep at TP550

I verified all transistors for the DLY'D sweep gen (5)

There does not appear to be a signal at AD (voltage is 0.2V).

I therefore checked TP355 on the delayed triggered board (3) and can see a signal at TP355.

Should I be searching why there is no signal at AD which may explain why there is no sweep at TP550?

Thanks

Thierry


Re: TEK 2215A info

Ozan
 

It is interesting to note that MOSTEK NVRAM has "PRE-QUAL" marking. Unless it means something else during that time, this looks like pre-production unit. It is common to give engineering samples to customers before the part is Qual'ed so that design can start early. However, for production these units are not suitable. This would suggest a prototype or demo unit.

ZN433CJ-10 datasheet shows 1Msps /10b ADC

Ozan


The newest date code I could spot was 1985, the Ferranti ZN433 ADC was
originally a 1MHz part but this ZN433CJ-10 might be faster. There is a
200nsec 2k x 8 NVRAM and no CPU visible on this board - maybe a second digital
board underneath, or does it manage to work with just the discrete logic on
the visible board? It would be very interesting to see how it works in live
mode, is it real time digitising only or does it cope with equivalent time
sampling at faster sweeps? The image in the photos library appears to show a
stored trace since there is nothing connected to the inputs, what happens when
you change the time/div for the stored image?

With an apparently limited storage capability it is difficult to imagine that
a customer would be willing to pay the development cost - any visible
inventory marks?

The ZN433CJ-10 is probably worth more than a standard 2215A , the only
reference I could I find was the avionics spares suppliers who charge enormous
prices for obsolete parts that are essential to keep the certification of
original kit.

A fascinating find!

Regards,

Roger


Photo 20210301_201121.jpg uploaded #photo-notice

TekScopes@groups.io Notification <noreply@...>
 

The following photos have been uploaded to the Tek 575 album of the TekScopes@groups.io group.

By: Joe <The-Lohrbach-Family@...>


Re: TEK 2215A info

 

Roger Evnas wrote:
There is a 200nsec 2k x 8 NVRAM and no CPU visible on this board - maybe a second
digital board underneath, or does it manage to work with just the discrete logic on the
visible board?
I think it's just the discrete logic. There are two ripple counters, one on the front side (74HC390) and one on the back side (74HC4040) that I think are used to generate memory addresses. There are a whole bunch of transparent latches (74HC573) two of which appear to be connected directly to the RAM. There's a differential amp on the front of the board, right behind the orange pin connector, that appears to be connected to the TRW chip, but I'd expect it to be feeding the Ferranti ADC (maybe those traces are on the back of the board, along with a bunch of traces for the memory address and data lines).

Not that I'm any kind of expert on any of this.

-- Jeff Dutky


Re: How to explain how negative feedback lowers noise?

Dave Peterson
 

FWIW, TTWIMC:

This topic, and other conversations relating to closed loop/feedback always take my mind back to the "Control Systems" class I took in school. Taught by Dr. Richard Dorf at UC Davis, textbook authored by same and R. Bishop. And actually lead by Dr. Dorf himself. No TAs.

I just found this on the UC Davis site:
https://engineering.ucdavis.edu/news/memoriam-professor-emeritus-richard-c-dick-dorf

There are a few educators that stood out in my education, and I count Dr. Dorf as one of them. I am saddened to find this news, but very honored to have had the opportunity to be taught by him. I wish I'd kept the textbook.

Dave


Re: How to explain how negative feedback lowers noise?

n4buq
 

Well, I hope no one tries to tell me that the Wright brothers didn't invent the airplane! ;-)

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Roy Thistle" <roy.thistle@mail.utoronto.ca>
To: TekScopes@groups.io
Sent: Monday, March 29, 2021 11:34:40 AM
Subject: Re: [TekScopes] How to explain how negative feedback lowers noise?

On Sun, Mar 28, 2021 at 04:12 PM, Jeff Dutky wrote:


The trouble with having all the world's knowledge at our fingertips is that
so
much of what so many know is wrong.
There's all sorts of things problematic with that statement; but, there is...
I would claim... a core of truth to it.
One consequence is that it takes more than an opinion... or more than an
opinion and an advanced STEM degree to opine "truthfully" on the topics of,
"Who discovered what," and "when and where it was discovered."
For instance, some once common tropes... now since revised... and being
revised.
Robert Fulton didn't invent the steam engine... but, maybe the first steam
powered boat?
Bell didn't invent the telephone.. but was the first to successfully patent
it in the U.S?
Farnsworth didn't invent the television... but was maybe the first to display
a transmitted image?
That is not to say all of these people were not very important contributors.
As for the "truth" of the genesis of of any particular invention... I'd say,
leave discovering it to the professionals: they are sometimes found,
hibernating under piles of dusty books, in a tiny closet of an office...
sequestered off from the mostly un-traveled corridors of the department of
Medieval Studies... or the like. Usually, such individuals have spent years,
if not their whole career, trying to answer "who" invented some particular
technology.
I know some people on this forum are incensed at the mention of the I.E.E.E.
;but, they do publish some well received monographs on topics concerning the
history of science and technology.
Other literature is less accessible... and typically in journals, or
university libraries.
--
Roy Thistle






Re: How to explain how negative feedback lowers noise?

Roy Thistle
 

On Sun, Mar 28, 2021 at 04:12 PM, Jeff Dutky wrote:


The trouble with having all the world's knowledge at our fingertips is that so
much of what so many know is wrong.
There's all sorts of things problematic with that statement; but, there is... I would claim... a core of truth to it.
One consequence is that it takes more than an opinion... or more than an opinion and an advanced STEM degree to opine "truthfully" on the topics of, "Who discovered what," and "when and where it was discovered."
For instance, some once common tropes... now since revised... and being revised.
Robert Fulton didn't invent the steam engine... but, maybe the first steam powered boat?
Bell didn't invent the telephone.. but was the first to successfully patent it in the U.S?
Farnsworth didn't invent the television... but was maybe the first to display a transmitted image?
That is not to say all of these people were not very important contributors.
As for the "truth" of the genesis of of any particular invention... I'd say, leave discovering it to the professionals: they are sometimes found, hibernating under piles of dusty books, in a tiny closet of an office... sequestered off from the mostly un-traveled corridors of the department of Medieval Studies... or the like. Usually, such individuals have spent years, if not their whole career, trying to answer "who" invented some particular technology.
I know some people on this forum are incensed at the mention of the I.E.E.E. ;but, they do publish some well received monographs on topics concerning the history of science and technology.
Other literature is less accessible... and typically in journals, or university libraries.
--
Roy Thistle


Re: TEK 2215A info

Ed Breya
 

I should mention that a clue to the timing and model line is the handle. That big fat ugly plastic handle on the lower end models provided a significant cost saving over the "classic" stainless steel one with plastic hubs found on other 2200s. I believe the pictures of the mystery scope discussed here show the classic handle, so it is more likely that it was a prototype or proof of concept model built on an actual 2215A carcass.

Ed


Re: TEK 2215A info

Ed Breya
 

The 2201 appears to be fairly close to this scope being discussed. Looks like several lower end analog/DSO models were developed. These would have appeared sometime after the 2230/2220 intro in 1985.

Ed


Re: TEK 2215A info

Roger Evans
 

The newest date code I could spot was 1985, the Ferranti ZN433 ADC was originally a 1MHz part but this ZN433CJ-10 might be faster. There is a 200nsec 2k x 8 NVRAM and no CPU visible on this board - maybe a second digital board underneath, or does it manage to work with just the discrete logic on the visible board? It would be very interesting to see how it works in live mode, is it real time digitising only or does it cope with equivalent time sampling at faster sweeps? The image in the photos library appears to show a stored trace since there is nothing connected to the inputs, what happens when you change the time/div for the stored image?

With an apparently limited storage capability it is difficult to imagine that a customer would be willing to pay the development cost - any visible inventory marks?

The ZN433CJ-10 is probably worth more than a standard 2215A , the only reference I could I find was the avionics spares suppliers who charge enormous prices for obsolete parts that are essential to keep the certification of original kit.

A fascinating find!

Regards,

Roger


Re: TEK 2215A info

Michael W. Lynch
 

Looking at the photographs of the boards it is apparent that this was a serious effort, not a hack job. The date codes on the IC's are all generally from 1984 -1985, so that is period correct. The construction quality is very good, looks like something TEK would do. As everyone states, there is no reference in the catalogs of such a scope. So this is one of those mysteries that comes along from time to time. Strange that someone would spend this much time, effort and money to modify a low end scope, but again, they built some T900 storage scopes as well. Indeed a very interesting piece of history. Needs to be investigated and preserved. Surely in the running for the rarest 22xx series scope?

--
Michael Lynch
Dardanelle, AR


Re: TEK 2215A info

 

Hi,
I agree with Ed, looks like a prototype or maybe a custom model for a customer. Could this be the only one of its type? Does the storage board look similar to any other 22xx boards?

Maurizio,
Where did you obtain the scope from, did the previous owner have any info on its history?

Regards,
John

3841 - 3860 of 184611