Date   

Re: New member and owner of a dead 2225

phillip.lyne.barrett
 

After a marathon session at distributor's web sites, I found a number of perfect fit replacement caps but still missing a few.

What is glaring is the absence of axial cap selection. It looks like these are disappearing fast. Not that I blame the manufacturers - I hate bending leads and would rather use SMDs any day. I was wrong about the axial caps' value - 15 uF, not 10. I wasn't able to find anything at mouser or digikey that matched except for some tant caps that were like $100. Since I need 7 of those, that ain't happening. These aren't in the power supply section so I don't HAVE to replace them. What are people doing in this situation? accepting worse tolerance? Significantly higher voltage (like 100+ for 10V caps), if that's even available?


There is a wonderful selection of SMD caps with tight tolerances for well less than a buck. I could imagine making a tiny little carrier board that would convert the SMD to the right pitch and size to replace an axial cap. Anything wrong with that idea?


Phil


Re: DIY TD Pulser

Eino Väänänen
 

I have also Tektronix 067-0513-00 with broken original tunnel diode. I have installed tunnel diode 1N3718 to GR-874 connector. Rise time is now 800 ps.


Eino


Re: are the 500 series scopes still usefull

Carl Hallberg
 

Hi Dave,
I had a 502. Bought it from work for $400 about 1967. Very sensitive input (100uV to 100KHz) and max B.W. of 1MHz on higher ranges. Limited use for me and ended up giving it away some years later. 502 had tubes for input and 502A was solid state input.
Carl
--------------------------------------------

On Sun, 11/12/17, Dave Seiter d.seiter@att.net [TekScopes] <TekScopes@yahoogroups.com> wrote:

Subject: Re: [TekScopes] are the 500 series scopes still usefull
To: "TekScopes@yahoogroups.com" <TekScopes@yahoogroups.com>
Date: Sunday, November 12, 2017, 9:30 PM

As were the 502 and 503.

-Dave



From: "Carl Hallberg n9ess@yahoo.com [TekScopes]"
<TekScopes@yahoogroups.com>

To: TekScopes@yahoogroups.com

Sent: Sunday, November 12, 2017 4:41 AM

Subject: Re: [TekScopes] are the 500 series scopes still
usefull


  Hi Bob,

The 547 is a single beam scope. It can be dual trace, 4
trace, etc, depending on plug-in. 555, 556 were dual beam.

Carl



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

On Fri, 11/10/17, Bob Albert bob91343@yahoo.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:

Subject: Re: [TekScopes] are the 500 series scopes still
usefull

To: TekScopes@yahoogroups.com

Date: Friday, November 10, 2017, 11:06 AM



The 530 series went to 15 MHz and the 540 series to 30 or
33

MHz.  The 580 to 80 MHz.  Plus, sampling units were

available to go a lot higher.  The high gain
differential

plug in and the calibrated offset plugin were really
nice,

and today's units don't have that.  My favorite
was

the 547 dual beam.

Bob


Re: New member and owner of a dead 2225

phillip.lyne.barrett
 

Thanks. I went through Mouser looking for the caps. 300 mil pitch doesn't seem to exist anymore. Will try Digi. On higher voltage caps, it's it the case the higher V often means higher ESR?

I am planning on pulling all the switcher electrolytic caps out and am hoping to find what went bad to help with the general diagnosis. Right now, my bet is on either C915 or C971. Hopefully the series regulator and inverter are ok as I don't have a scope to debug my scope with...


As to Dave, it's not his Aussie accent and turn of phrase, rather his high pitched voice and geeky mannerisms that bug my Wife. It sometimes gets a bit wearing to me too. Plus it can be hard to figure out if he thinks something is good or bad. I went to school with a bunch of Aussies - great group of friends.


Re: New member and owner of a dead 2225

 

On 14 Nov 2017 07:18:45 +0000, you wrote:

I've seen those videos. Dave's tear down is really good though my wife makes me wear headphones for any of his videos - she's a non-fan. I kind of get her point...
Crikey! Dave's Australian speech makes for entertaining listening but
I can understand how it would get old after a while. The same thing
happens to me if I binge watch Doctor Who episodes.

After following the circuits on the schematic, I think the 38V/67.5V feeds are probably OK because there doesn't seem to be anything particularly sensitive there. Two 100n 50V ceramics are worth looking at, one on the X-Axis Amp and one in the vertical output amp. Everything else feeds though resistors. Though the lowest is 330 so bears looking at a bit more.
Damage to the vertical CRT amplifier transistors is possible.
Depending on the bias conditions which are not real clear with the
power supply malfunctioning, the 2N3866s could have a specified
maximum breakdown voltage between Vceo of 30 volts and Vcbo of 55
volts. Luckily they should be easy to replace if damaged.

I am surprised that the switching preregulator did not include an SCR
crowbar circuit to protect against a shorted switching transistor but
maybe Tektronix determined that it was not necessary.

On the caps, I've found what look like decent replacements - reasonably low ESR, same or better tolerance and all are 105C. However, not a single lead pitch matches. I can make them fit by bending the leads in an L to make them fit the original pitch. I assume that there is no issue with that. So, not worried except for C900 - the big 2200 uF 80V on the mains input board. The only matches are snap-in caps with fat, stiff, stubby leads and the wrong terminal pitch. (10mm vs a measured 12mm on the one that's there now). I guess I can make a little adapter but it will be a bit ugly. If I was industrious, I'd 3D print a foot for it to keep it from moving around - though it will probably be hot glued instead.
Usually capacitors with the correct lead pitch can be found. Higher
voltage parts can be selected if necessary and this may even be
desirable for improved reliability and operating life.

The big bulk input capacitor is one of the aluminum electrolytics
which is likely to last the longest so maybe leaving it in place would
be best unless testing shows that it has failed. The reason for this
is that it was originally selected based on capacitance instead of ESR
or ripple current rating which will be more than enough and it is the
last one which impacts operating life.

Another question. There are at least 9 10 uF axial electrolytics in various places. I should replace them as well? I'm not wild about removing the attenuator/timebase board, though it's probably easier than it looks.
They will not have caused the failure but replacing them may lead to
better performance and perhaps less noise in the displayed trace. On
the other hand, replacing parts unnecessarily risks causing damage.

Once I get my ESR meter (due this Friday), I'll hopefully find a smoking gun.
Unfortunately an ESR meter will consider a shorted capacitor good.
They are useful and convenient for in-circuit measurements but not
always easy to interpret.

Soon your 2225 will be operating with peak efficiency and Bob's your
uncle!

You should hear some of the San Dimas slang I picked up when I worked
there which was not featured in the Bill and Ted movies.


Re: A fool and his money ...OR ... moneywell spent

 

On 13 Nov 2017 18:11:41 +0000, you wrote:

I got the Agilent probes and they seem to be performing well with the Tek 2465 CTS but I really can't check the upper part of the bandwidth. I looked at getting a Tektronix 067-0681-01 (Calibration fixture / tunnel diode pulser) and was quite shocked on the availability and cost - more than I paid for the scope, shipping, and three of the four probes. Guess I'll be on the lookout for one of these. Not going to pay $250 that some folks want for these.
Oh, and I forgot to mention that this is not something I would worry a
great deal about. Even without adjustment, the Agilent probes will be
close and you are unlikely to be measuring any signals with high
impedance passive probes that will reveal a problem because of the
relatively high probe loading at 300 MHz and higher.


Re: DIY TD Pulser

Craig Sawyers <c.sawyers@...>
 

Alternatively, the UKP50 pulser we discussed a month or two back that does <40ps.

http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=124&products_id=295&zenid=e90df0d242b960a20cbff2cb95ed16f3

The calibration data that came with mine was ~31ps. Although technically there are some aberrations
probably as a result of the BNC connector, they would possibly only be visible if pushing the limits
of an S4 or S6 sampling head. For a 7104 the rise is exceptionally clean and verifies a system rise
time of 350ps with 7A29's.

Unless the idea is to try and make a Tek TD pulser as a technical challenge. Which is absolutely fine
of course - I totally understand that!

Craig

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com]
Sent: 14 November 2017 04:19
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: DIY TD Pulser

Pardon, two of the 067-0513-00 pulse generators that David
mentioned wanting to see the inside of.

Which can be arranged, as I have two of them.

-Chuck Harris

Jeff Davis n0dyjeff@hotmail.com [TekScopes] wrote:
Not sure what exactly you have two of... ??


I've posted some test results from two samples of the build I did following the notes from Sergey
Kubushyn. The test was conducted over the noon hour on an 8 GHz digital Tektronix scope at work -
didn't catch the exact model number.

I posted captures of the rise time photos under "DIY TD Pulser" in the Photos section. Got 159 pS
on
the first build. Was a little more careful with the output construction on the second and got down
to
119 pS with it.


Jeff


________________________________
From: TekScopes@yahoogroups.com <TekScopes@yahoogroups.com> on behalf of Chuck Harris
cfharris@erols.com [TekScopes] <TekScopes@yahoogroups.com>
Sent: Monday, November 13, 2017 6:46 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: DIY TD Pulser



I have two of them. One has a bad TD, the other works, but
is easily 10 times slower than the spec's say it should be.

I had heard that when tektronix made them they had no real
way of measuring the pulse risetime, so they guessed.

-Chuck Harris

David davidwhess@gmail.com [TekScopes] wrote:
Why can't you use the random sampling capability on the 7T11? Then at
least no delay line should be required. A power divider might still
be desirable to separate the sampling kickout from the trigger.

Tektronix had a slightly more complex tunnel diode pulse generator
which generated a pretrigger:

<http://w140.com/tekwiki/wiki/067-0513-00>

It would be interesting to see the inside to see how it was
constructed.

------------------------------------
Posted by: Chuck Harris <cfharris@erols.com>
------------------------------------


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

Yahoo Groups Links



Re: New member and owner of a dead 2225

phillip.lyne.barrett
 

Thanks, David, Tom, Tom and Glen.

I've seen those videos. Dave's tear down is really good though my wife makes me wear headphones for any of his videos - she's a non-fan. I kind of get her point...

After following the circuits on the schematic, I think the 38V/67.5V feeds are probably OK because there doesn't seem to be anything particularly sensitive there. Two 100n 50V ceramics are worth looking at, one on the X-Axis Amp and one in the vertical output amp. Everything else feeds though resistors. Though the lowest is 330 so bears looking at a bit more.


It looks like Q912 is not blown, at least a resistance check across the collector and base sees a cap charging up - probably C909 though the 2.2K resistor on the base. Not sure how to determine if either TL594 is dead. I've got the datasheet but haven't looked yet. Will probably order a few just in case, they're cheap.


On the caps, I've found what look like decent replacements - reasonably low ESR, same or better tolerance and all are 105C. However, not a single lead pitch matches. I can make them fit by bending the leads in an L to make them fit the original pitch. I assume that there is no issue with that. So, not worried except for C900 - the big 2200 uF 80V on the mains input board. The only matches are snap-in caps with fat, stiff, stubby leads and the wrong terminal pitch. (10mm vs a measured 12mm on the one that's there now). I guess I can make a little adapter but it will be a bit ugly. If I was industrious, I'd 3D print a foot for it to keep it from moving around - though it will probably be hot glued instead.


Another question. There are at least 9 10 uF axial electrolytics in various places. I should replace them as well? I'm not wild about removing the attenuator/timebase board, though it's probably easier than it looks.


Once I get my ESR meter (due this Friday), I'll hopefully find a smoking gun.


Anyway, again, thanks for all the help. I really do appreciate all your efforts.


Phil


Re: DIY TD Pulser

Chuck Harris <cfharris@...>
 

Pardon, two of the 067-0513-00 pulse generators that David
mentioned wanting to see the inside of.

Which can be arranged, as I have two of them.

-Chuck Harris

Jeff Davis n0dyjeff@hotmail.com [TekScopes] wrote:

Not sure what exactly you have two of... 😊


I've posted some test results from two samples of the build I did following the notes from Sergey Kubushyn. The test was conducted over the noon hour on an 8 GHz digital Tektronix scope at work - didn't catch the exact model number.

I posted captures of the rise time photos under "DIY TD Pulser" in the Photos section. Got 159 pS on the first build. Was a little more careful with the output construction on the second and got down to 119 pS with it.


Jeff


________________________________
From: TekScopes@yahoogroups.com <TekScopes@yahoogroups.com> on behalf of Chuck Harris cfharris@erols.com [TekScopes] <TekScopes@yahoogroups.com>
Sent: Monday, November 13, 2017 6:46 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: DIY TD Pulser



I have two of them. One has a bad TD, the other works, but
is easily 10 times slower than the spec's say it should be.

I had heard that when tektronix made them they had no real
way of measuring the pulse risetime, so they guessed.

-Chuck Harris

David davidwhess@gmail.com [TekScopes] wrote:
Why can't you use the random sampling capability on the 7T11? Then at
least no delay line should be required. A power divider might still
be desirable to separate the sampling kickout from the trigger.

Tektronix had a slightly more complex tunnel diode pulse generator
which generated a pretrigger:

<http://w140.com/tekwiki/wiki/067-0513-00>

It would be interesting to see the inside to see how it was
constructed.


Re: DIY TD Pulser

Jeff Davis
 

Not sure what exactly you have two of... 😊


I've posted some test results from two samples of the build I did following the notes from Sergey Kubushyn. The test was conducted over the noon hour on an 8 GHz digital Tektronix scope at work - didn't catch the exact model number.

I posted captures of the rise time photos under "DIY TD Pulser" in the Photos section. Got 159 pS on the first build. Was a little more careful with the output construction on the second and got down to 119 pS with it.


Jeff


________________________________
From: TekScopes@yahoogroups.com <TekScopes@yahoogroups.com> on behalf of Chuck Harris cfharris@erols.com [TekScopes] <TekScopes@yahoogroups.com>
Sent: Monday, November 13, 2017 6:46 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: DIY TD Pulser



I have two of them. One has a bad TD, the other works, but
is easily 10 times slower than the spec's say it should be.

I had heard that when tektronix made them they had no real
way of measuring the pulse risetime, so they guessed.

-Chuck Harris

David davidwhess@gmail.com [TekScopes] wrote:
Why can't you use the random sampling capability on the 7T11? Then at
least no delay line should be required. A power divider might still
be desirable to separate the sampling kickout from the trigger.

Tektronix had a slightly more complex tunnel diode pulse generator
which generated a pretrigger:

<http://w140.com/tekwiki/wiki/067-0513-00>

It would be interesting to see the inside to see how it was
constructed.

On Mon, 13 Nov 2017 23:53:05 +0000, you wrote:

Hey Joseph,

I built one of those, and the complexity/value is not in the circuit. It's
mostly in the characterization of the behavior of the physical construction
of the circuit. Mine has a rise time of ~200ps, as determined by my TDS
784D and some maths. Plenty good to calibrate the transient response of my
485 and 2467, though I do worry about the pre-shoot and overshoot I see on
the TDS.
I'll need to look closer one day, now that I have a 7834, 7S11/7T11 - just
need a decent power splitter and a delay line, and a few more little things
:).

Siggi

------------------------------------
Posted by: David <davidwhess@gmail.com>
------------------------------------


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

Yahoo Groups Links




Engine Analyzer Plug-In Modification

Gary Robert Bosworth
 

Does anyone know the specific modification that was done to the 2B67 horizontal sweep plug-in to make it work with the Engine Analyzer that Tektronix offered back in the 1960's and 1970's? Physically, does it show on the outside of the plug-in?


Re: DIY TD Pulser

Chuck Harris <cfharris@...>
 

I have two of them. One has a bad TD, the other works, but
is easily 10 times slower than the spec's say it should be.

I had heard that when tektronix made them they had no real
way of measuring the pulse risetime, so they guessed.

-Chuck Harris

David davidwhess@gmail.com [TekScopes] wrote:

Why can't you use the random sampling capability on the 7T11? Then at
least no delay line should be required. A power divider might still
be desirable to separate the sampling kickout from the trigger.

Tektronix had a slightly more complex tunnel diode pulse generator
which generated a pretrigger:

<http://w140.com/tekwiki/wiki/067-0513-00>

It would be interesting to see the inside to see how it was
constructed.

On Mon, 13 Nov 2017 23:53:05 +0000, you wrote:

Hey Joseph,

I built one of those, and the complexity/value is not in the circuit. It's
mostly in the characterization of the behavior of the physical construction
of the circuit. Mine has a rise time of ~200ps, as determined by my TDS
784D and some maths. Plenty good to calibrate the transient response of my
485 and 2467, though I do worry about the pre-shoot and overshoot I see on
the TDS.
I'll need to look closer one day, now that I have a 7834, 7S11/7T11 - just
need a decent power splitter and a delay line, and a few more little things
:).

Siggi

------------------------------------
Posted by: David <davidwhess@gmail.com>
------------------------------------


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

Yahoo Groups Links




317 in Lyons, Colorado

Kurt Rosenfeld
 


Re: A fool and his money ...OR ... moneywell spent

 

On 13 Nov 2017 18:11:41 +0000, you wrote:

The test is to coaxially connect the probe tip through a 50 ohm feedthrough termination (Tektronix made this as a special adapter) to
a fast reference level pulse generator like a PG506 (not quite fast enough) or tunnel diode pulser like the Tektronix 067-0681-01 which is what was actually recommended for the 2465 calibration. Then the transient response can be compared with and without the probe on the oscilloscope itself.
I got the Agilent probes and they seem to be performing well with the Tek 2465 CTS but I really can't check the upper part of the bandwidth. I looked at getting a Tektronix 067-0681-01 (Calibration fixture / tunnel diode pulser) and was quite shocked on the availability and cost - more than I paid for the scope, shipping, and three of the four probes. Guess I'll be on the lookout for one of these. Not going to pay $250 that some folks want for these.
The Tektronix 067-0681-01 in particular is pretty expensive but I
think that is because there is high demand from those who do not know
of alternatives.

The Tektronix 067-0513-00 and Type 284 tunnel diode pulse generators
could also be used with a GR874 adapter. Tektronix even made GR874
feedthrough termination to coaxial probe tip adapters which are
intended for exactly this application; the part numbers are
017-0088-00 for miniature probe tips and 017-0520-00 for subminiature
probe tips. They were intended for low-z and active probes much
faster than 300 MHz so would be overkill for your application.

There are some other hobby level fast edge pulse generators available
which could be used. Some are avalanche transistor based and others
use the output signal from a CML or ECL gate.

<https://www.eevblog.com/forum/projects/yet-another-fast-edge-pulse-generator/>
<http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=124&products_id=295>


Tektronix 485s for sale

Dave Daniel
 

All,

Due to mounting pressures to sell my property I need to unload a few test equipment items.

I have two Tektronix 485s that I think I need to sell. I have powered them up and performed very basic testing. I have limited time and don't plan to do any exhaustive testing on either of them. They are not in calibration.

Below are descriptions:

1. Tektronix 485. It has serial number B192687. It has Option 78 - P11 phosphor. It is in good cosmetic shape. Channel 1 is rock-solid while channel 2 is a bit jittery; I suspect the front panel controls need cleaning. It has the rare front panel snap-on plastic cover. $300.

2. Tektronix 485. It has serial number B155872. Some of the button legends are worn off; I placed white label-printer labels with the legends on most of the buttons where the legends were missing. The mode buttons on this 'scope are in serious need of electrical cleaning. They operate stiffly and do not fully switch between modes (for instance, when the mode is set to CH1 or CH2, there is a second trace on the screen, as if the mode is really "sort of" ALT or "sort of" CHOP; putting additional pressure on the CH1/CH2 mode button eliminates the second trace). It also has the rare front panel snap-on plastic cover. I think I might have a few button caps that could be used to replace the ones on this 'scope where the legends are worn off; I will need to check. If so, I will include whatever I have with the 'scope. If not, Walter at Sphere or Qservice (or someplace else) may have them. $250.

I would like to sell these for the prices listed above plus the cost of shipping (and maybe for packaging materials if I have to buy them), more or less. The prices are negotiable; we'll see what responses I get. I will endeavor to pack them well so that they are not damaged in transit (I've shipped several largish Tektronix products around the globe and have not had any complaints, and received one compliment). I would use either USPS or UPS (not FedEx) at the buyer's discretion. Local pickup in the Lyons, Colorado (front range) area would be preferable. Payment would be by PayPal or cleared personal check.

I have one original manual which I would include for $10 with one of the 485s. I believe I have a printed copy of a PDF of the manual and, if I can find it, I would include that with the other 485. If not, then the other 485 would come without a manual.

If you are interested PLEASE CONTACT ME PRIVATELY using "kc0wjn at gmail dot com". Please do not reply to the list (I will ignore any such replies).

I am not at all pleased about having to sell these, as I had a 485 as one of my two "personal" 'scopes for many years at StorageTek many years ago and these 'scopes are old friends. But I think this is probably the right thing to do.

I also have a partially-working HP 8558B/853A spec an combo that I also need to sell, if anyone is interested in that.

Thanks for the bandwidth.

DaveD


Re: New member and owner of a dead 2225

n4mf_sc
 

I have the 1982 version I think and one from a website that is no longer there called Tek-cross-ref-free. It has a sig in the pdf of www.aa4df.com http://www.aa4df.com which is available for someone to purchase but no longer online. I can't post either because they are way past the limit on upload sizes. Transistors and IC's are in both..

Mitch
N4MF


Re: New member and owner of a dead 2225

Tom Jobe <tomjobe@...>
 

Hi Phillip.
I see you are getting some very good help on this problem, and when you
combine that with the fact that your voltages are only down by half, I'd
say the 2225 is only lightly wounded and that you will have it working
perfectly very soon. In order for the low voltages to be half there,
most of the power supply must be fundamentally sound.
The 2225 needs all of the aluminum electrolytic capacitors 10 uF and
larger changed anyway to regain that sharp trace you once had, and the
new ones might possibly help with your current problem as well. Get
brand new high quality 105 degree caps from a major electronics parts
supplier if you can.
There are several variations of the architecture of the small 22xx power
supplies but there are not many problems with the 2225 type of power
supply that ever show up on the Tekscopes Group .
When I read your original post about your 2225 problem, I looked on
YouTube to see what kinds of videos were available about the 2225.
Take a look at these two when you have time. This 2225 Dave Jones bought
worked just as it was received, and he gives you quite a nice lesson on
its use and claibration, as well as a tour of much of it's inner
workings (less the power supply unfortunately). He also gives you some
good common sense tips about working around the high voltages present in
the oscilloscope.

EEVBlog #196 operational review of the 2225
https://www.youtube.com/watch?v=8GR_6QH3uZk

EEVBlog #208 teardown and calibration of the 2225
https://www.youtube.com/watch?v=mHODWDBcQDg

Best of luck!
tom jobe...




On 11/12/2017 3:29 PM, phillip.lyne.barrett@gmail.com [TekScopes] wrote:

Long term electronics hobbyist. I've had a Tek 2225 for about 15 years
and used it a lot. The other day I turned it on to test a circuit I'm
prototyping and nothing. Dead. Check outlet, fuse, power cord. Nope.
The only sign of life is a little blip on the power and leds - maybe
half a second. I'm guessing it's the power supply. This scope has been
an old friend.


I got the service manual and pulled the chassis out of the case. Found
a loose torx screw inside though It didn't appear to be shorting
anything and after removing it the symptoms persist. The scope had
been sitting on the bench in the same spot for a couple of years so I
doubt the screw was the problem. Inspection didn't show anything
obvious - burnt components, bulging caps, blue smoke. In fact, it was
surprisingly clean for 30 year old scope.


Anyway, I took some test point measurements on the bottom of the main
baord and all the voltage levels were around half what they were
supposed to be. More confident it's the PS. Looked at the mains input
board. rectifiers (CR901-CR904) are ok. Pulled the board and pulled
the big @ss 2200 uF cap (C900). It tested out ok (2270 uF).


Next step is to look at the preregulator section after I put the mains
input board back.


I'm just following a fairly logical path here but thought there might
be smarter people than me here that could help short cut the process.
Any suggestions of where to look would be greatly appreciated.


Phil

[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Re: DIY TD Pulser

 

Why can't you use the random sampling capability on the 7T11? Then at
least no delay line should be required. A power divider might still
be desirable to separate the sampling kickout from the trigger.

Tektronix had a slightly more complex tunnel diode pulse generator
which generated a pretrigger:

<http://w140.com/tekwiki/wiki/067-0513-00>

It would be interesting to see the inside to see how it was
constructed.

On Mon, 13 Nov 2017 23:53:05 +0000, you wrote:

Hey Joseph,

I built one of those, and the complexity/value is not in the circuit. It's
mostly in the characterization of the behavior of the physical construction
of the circuit. Mine has a rise time of ~200ps, as determined by my TDS
784D and some maths. Plenty good to calibrate the transient response of my
485 and 2467, though I do worry about the pre-shoot and overshoot I see on
the TDS.
I'll need to look closer one day, now that I have a 7834, 7S11/7T11 - just
need a decent power splitter and a delay line, and a few more little things
:).

Siggi


Re: New member and owner of a dead 2225

 

I think U940 would have been overvoltaged. Max is 41 volts. It would have seen 67 - 15 or 52 volts. But those are very cheap and available. C972, 470/50v could have survived a 17 volt overvoltage. But they are cheap and available. I agree Q912 is probably ok as long as the stressor didn't get it before 913 shorted.

Hell, I would sure try to bring it back to life.

Tom

----- Original Message -----
From: David davidwhess@gmail.com [TekScopes]
To: TekScopes@yahoogroups.com
Sent: Monday, November 13, 2017 6:12 PM
Subject: Re: [TekScopes] New member and owner of a dead 2225



A shorted Q913 should have protected driver Q912. Q911 should have
protected TL594 U910.

The linear series regulator would have tried to control the output
voltages until Q923 overheated and likely failed shorted. Switching
regulator controller U940, another TL594, operates open loop to drive
the inverter but uses one of its error amplifiers to detect the supply
voltage to the inverter and if it rises above 42.5 volts, it shuts
down so the rest of the oscilloscope circuits should be protected.

I am not sure about how the +40 volt supply rising to +67.5 volts is
going to affect the sweep circuit on schematic 5 and the vertical CRT
amplifier on schematic 5. Normally both circuits should be able to
protect themselves until they overheat but when the low voltage
outputs shut off, they may not be able to. I am inclined to believe
Tektronix took this into account but the theory section says nothing
about Q913 failing as a short.

On Mon, 13 Nov 2017 01:01:56 -0500, you wrote:

>That's not good. The Q913 is a TIP30C and is available pretty cheap. The analog pass xistor Q923 is also on ebay. You should also check the driver to Q913, Q912. Probably pull Q913 to double check it and follow up with some other measurements.
>
>The switching regulator is a TL594. They are common. Two are used. probably both are now toast.
>
>You will need to check everything that is supplied the pre-regulated voltage (38 volts) as it would have exceeded many ratings. Besides the power supply schematic #7, check schematics 2 and 5 as this overvoltage goes to those sections.
>
>Good luck,
>Tom M


Re: DIY TD Pulser

Siggi
 

Hey Joseph,

I built one of those, and the complexity/value is not in the circuit. It's
mostly in the characterization of the behavior of the physical construction
of the circuit. Mine has a rise time of ~200ps, as determined by my TDS
784D and some maths. Plenty good to calibrate the transient response of my
485 and 2467, though I do worry about the pre-shoot and overshoot I see on
the TDS.
I'll need to look closer one day, now that I have a 7834, 7S11/7T11 - just
need a decent power splitter and a delay line, and a few more little things
:).

Siggi

On Mon, 13 Nov 2017 at 18:14 joseph@danyabutter.com [TekScopes] <
TekScopes@yahoogroups.com> wrote:



Sergey - thanks for the information. I looked at the schematic from the
data sheet and you are correct, this is not a very complex circuit. Not
sure why folks want over $200 for it. Guess they are hard to come by - law
of supply and demand.

40301 - 40320 of 182078