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Re: Odd 453A on ebay UK

John
 

Well, it's now listed for (minimum) third time.
Desciption states it's a "dual beam" scope, so I do hope someone can politely correct him on this: don't want it sold and then rejected as "not as described" , do we?
john


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

John
 

Joe:
congratulations, and I hope you enjoy using this wonderful piece of test equipment. I had a very simlar experience with a 575 which I bought "blind" on an auction site a couple of years ago (not Ebay). I've managed to retain the HV electrolytics, but changed all the black jobbies. On my unit, there were quite a few tired valves/tubes: in particular the triodes used as HT regulators. Oh, and the fan bearings were sticky with old green oil, so the fan would not run until things got hot. It took some effort to completely clean the oilite bearings.
John


Re: Tek 2430 Works Fine for 15mins Then Freezes

Siggi
 

On Tue, Mar 30, 2021 at 10:02 AM John Morris <k7rld@comcast.net> wrote:

Scopes are not my expertise so if anyone has an idea where to start
looking, I'd sure appreciate some guidance.
You'd generally start by looking at the power supplies which may simply
need recapping by now.


Re: FS: Tektronix Scope-Mobile 200C

Dave Seiter
 

Grin!  The 7704A probably isn't recommended, but I've had one on that cart for years.  Just last week I was thinking that my 465 would make more sense on it (and be safer!)

On Tuesday, March 30, 2021, 10:29:37 AM PDT, ppppenguin <tekscopes@borinsky.co.uk> wrote:

Hi Dave, I didn't realise that. But then I've never worked with 7000 series kit. I don't think it would take my 547:)


Re: FS: Tektronix Scope-Mobile 200C

ppppenguin
 

Hi Dave, I didn't realise that. But then I've never worked with 7000 series kit. I don't think it would take my 547:)


Re: FS: Tektronix Scope-Mobile 200C

Dave Seiter
 

Also works for 7704As, well strapped down, of course!

On Tuesday, March 30, 2021, 02:40:16 AM PDT, ppppenguin <tekscopes@borinsky.co.uk> wrote:

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/


5000 Series Scope Deflection Plate Driver Transistors

Jim Adney
 

Many years ago, in a former life and former employer, I was using a 5112 Dual Beam Scope that was perfect for my project. The 2 MHz bandwidth was plenty for what we were doing and, while the dual beam wasn't really necessary, it gave us confidence that what we were shown on the screen was actually coincident in time. This scope, however, had a problem. It would occasionally stop showing one half of one of the traces. The EEs with me on this project would "fix" this by removing the affected plugin and SLAMMING it back into place. The shock often cured the problem, but this "solution" annoyed me.

I managed to get the scope manual and noticed that there were 6 identical output transistors which drove the 6 deflection plates, 4 vertical and 2 horizontal. This scope had dual beams, but only one time base. Reading thru the circuit description I could see that each transistor drove its beam over half the screen. So I figured out which transistor seemed like it might be the problem and swapped it to a different location. This was easy because they were in sockets. Sure enough, the next time the problem occurred, it was in that new location, and I found that I could make the problem come and go by tapping that transistor.

The manual gave a Tek part number for that transistor and also a suitable replacement from some Japanese manufacturer. I ordered 2 or 3 of the Jap replacements, so I would have spares. I replaced the bad transistor and taped the spares inside the scope case, in a zip lock bag. A couple months/years later, another of the OE transistors failed and then another. I ordered more spares, and eventually used all of them. As far as I know, the replacements never failed.

So the question is, was this a well known problem with these transistors and were these common to all the 5000 series 2 MHz scopes? The scope was probably 10-15 years old by the time I started replacing transistors, but I'd never run into streaks of failing parts like this before. Sorry, but I don't remember the Tek part number or the Japanese replacement; this was circa 1985-1990.

Other than those problem transistors, I really liked that scope.


Re: Tek 2430 Works Fine for 15mins Then Freezes

 

Is the fan running? Is there a lot of dust on the heat sink fins?

On 3/20/2021 5:40 PM, John Morris wrote:
I've got a TEK 2430 that seems to work just fine for about 15 mins. Sometimes more. All tests PASS.
I've input a function generator and all different inputs look fine on both channels. Then after 15 mins and sometimes more, I'll look over at it and the screen is still showing a nice looking sine wave, for instance that I've input, but when I go to make a change, the scope is frozen with that image and no other controls seem to make a change.
Relays click when I make some control changes but the screen remains frozen with that sine wave image.
When I turn the scope off and wait 20-30 secs and then turn it back on, it will show the standard horizontal line but will not detect an input.
I can turn the scope completely off and after a few hours it will again come up and work just fine but eventually the same thing happens.
Scopes are not my expertise so if anyone has an idea where to start looking, I'd sure appreciate some guidance.
Thank you. John / K7RLD



--
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Re: FS: Tek 206-0104-00 Straight Tips for 6-32 Probes

Jim Adney
 

5 of these have now been sold. I'd like to keep 5 for myself, so that leaves 10 still available.


Re: Repair of Set Screw Attachment for Tek-made VAR Pots

Jim Adney
 

On Fri, Mar 26, 2021 at 09:39 PM, Dave Wise wrote:

You ought to upload the article to TekWiki at w140.com .
Okay, done. Took me awhile to figure out where and how to do this, but I think I (pretty much) managed.

https://w140.com/tekwiki/wiki/Potentiometers/Repairs


TEK 2430 Works Fine and then Freezes

John Morris
 

I have a 2430 that PASSES all tests and works fine on both channels using a function generator. After a minimum of 30 mins, sometimes longer, the screen will freeze and no controls will change it. The last curve will be frozen on the screen.
If I turn it off and then back on after waiting 30 secs or so, it will not boot up at all sometimes and sometimes it will go to a horizontal trace but no input will show on the screen.
If I turn it off for several hours and then back on, everything is fine again for another 30 mins or so and sometimes up to several hours. Then the screen with a trace will freeze up again. I can hear the relays clicking as i change the timebase but it changes nothing on the trace. The curve screen position controls change nothing either.
If anyone has seen this before and can point me in the right direction, it would be very much appreciated.

John / K7RLD


Tek 2430 Works Fine for 15mins Then Freezes

John Morris
 

I've got a TEK 2430 that seems to work just fine for about 15 mins. Sometimes more. All tests PASS.
I've input a function generator and all different inputs look fine on both channels. Then after 15 mins and sometimes more, I'll look over at it and the screen is still showing a nice looking sine wave, for instance that I've input, but when I go to make a change, the scope is frozen with that image and no other controls seem to make a change.
Relays click when I make some control changes but the screen remains frozen with that sine wave image.
When I turn the scope off and wait 20-30 secs and then turn it back on, it will show the standard horizontal line but will not detect an input.
I can turn the scope completely off and after a few hours it will again come up and work just fine but eventually the same thing happens.
Scopes are not my expertise so if anyone has an idea where to start looking, I'd sure appreciate some guidance.
Thank you. John / K7RLD


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.

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