Author Topic: Tektronix 2901 Time Mark Generator Tear Down & Inspection  (Read 37205 times)

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Online BravoVTopic starter

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #25 on: April 18, 2014, 02:11:44 am »
Thanks for the bump, this thread is quite old that I almost forgot that I created it.

Btw, this gadget since it was bought, its frequently borrowed among friends used it as comb generator to check their analog spectrum analyzers.  ::)

Offline marcuswilson

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #26 on: October 31, 2014, 01:17:17 am »

Why used two different wires type instead of just using the copper enameled for both ?

Because the silver or nickel one solders in instantly and the enamelled one needs to have it's ends cleaned, so it's only used where insulation is required.
 

Online Alex Eisenhut

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #27 on: October 31, 2014, 12:34:55 pm »
Just be careful with that diode in the clip in the 500MHz section. I lost mine and it's impossible to find a substitute.
Hoarder of 8-bit Commodore relics and 1960s Tektronix 500-series stuff. Unconventional interior decorator.
 

Offline TerraHertz

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #28 on: November 07, 2014, 07:09:29 am »
Just be careful with that diode in the clip in the 500MHz section. I lost mine and it's impossible to find a substitute.

I was wondering about that. While admiring the photos I noticed that tiny little thing positively glowing with essence of gold-plated unobtainium.

What is it, a tunnel diode as the active element in that stripline oscillator?

Now I'm all envious and want to buy one of these things. Too bad the current ebay crop is quite high priced.
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Online Alex Eisenhut

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #29 on: November 07, 2014, 03:40:38 pm »
Just be careful with that diode in the clip in the 500MHz section. I lost mine and it's impossible to find a substitute.

I was wondering about that. While admiring the photos I noticed that tiny little thing positively glowing with essence of gold-plated unobtainium.

What is it, a tunnel diode as the active element in that stripline oscillator?

Now I'm all envious and want to buy one of these things. Too bad the current ebay crop is quite high priced.

It's a varactor used in the frequency multiplier. I don't know how it works so I don't know what modern part you could shove in there.

The OCXO in my 2901 is not great, you can see the frequency shift up and down as the oven turns on and off. It's quite crude.
Hoarder of 8-bit Commodore relics and 1960s Tektronix 500-series stuff. Unconventional interior decorator.
 

Offline Chipguy

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #30 on: November 07, 2014, 06:54:03 pm »
Awesome!

IC's with datecodes starting with 69  :-+
You don't see that very often  :)
Where is that smoke coming from?
 

Offline TerraHertz

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #31 on: November 08, 2014, 12:27:36 pm »
Do the videos here http://www.vintagetek.org/video-gallery/   work for you?
The page source has them as Flash things, and none are working for me.  Not sure if due to my browser, or their server.

Alternatively, does anyone know of copies hosted anywhere else in a normal video format, that can be downloaded and saved locally?

Edit: Nevermind the 2nd, I found:
  https://www.eevblog.com/forum/testgear/historic-tektronix-videos-back-online-neat-stuff-for-test-equipment-geeks!/
  ft p://www.helpedia.com/pub/mirrors/www.vintagetek.org/video-gallery/   (remove space)
« Last Edit: November 08, 2014, 12:35:27 pm by TerraHertz »
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Offline David Hess

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #32 on: November 08, 2014, 05:25:07 pm »
Great pictures. I wonder why the sockets for small signal transistors. Was this a holdover from the tube days which would have to replaced regularly? I remember that some manuals mention that it's not recommended to periodically remove and check semiconductors, suggesting that it is recommended for some equipment. It may also be because they considered semiconductors expensive, just like how people often used sockets for expensive DIP parts. Not much choice now most expensive parts are BGA, however.

I think the sockets cause more issues due to bad connections than they solve by making part replacement easier.

In the past transistors were less reliable and relatively more expensive so the extra cost of using sockets was small.  Eventually reliability become high enough that the sockets themselves caused more failures than bad transistors so they stopped using them.

This also happened with ICs and IC sockets although in this case it may have been helped along by those cheap edge wipe sockets Texas Instruments made which were unusually unreliable.

Just be careful with that diode in the clip in the 500MHz section. I lost mine and it's impossible to find a substitute.

I was wondering about that. While admiring the photos I noticed that tiny little thing positively glowing with essence of gold-plated unobtainium.

What is it, a tunnel diode as the active element in that stripline oscillator?

Now I'm all envious and want to buy one of these things. Too bad the current ebay crop is quite high priced.

It's a varactor used in the frequency multiplier. I don't know how it works so I don't know what modern part you could shove in there.

Varactor multipliers rely on non-linear change in reactance whereas normal diode multipliers rely on non-linear change in resistance.  Varactor multipliers are higher efficiency but have much narrower bandwidths and are more difficult to tune.  In the schematic you can see where they used a pair of tuned circuits (idlers) to short out two of the harmonics; probably the 2nd and 3rd.  (I just now looked in the theory section and it was indeed the 2nd and 3rd.)

The specifications for the diode Tektronix used are available and it would not be difficult to find a suitable surface mount varactor diode to replace it.  They are not expensive so a bunch of different diodes could be evaluated to find the best one.

Quote
The OCXO in my 2901 is not great, you can see the frequency shift up and down as the oven turns on and off. It's quite crude.

The earlier type 184 time mark generator uses the same OCXO with the on-off oven.  I never understood what application Tektronix had in mind for these which would require an OCXO.  Analog sweep calibration does not require this kind of accuracy.
 

Offline TerraHertz

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #33 on: December 09, 2014, 08:52:31 am »
Yay! Got one! Ebay 151502733003. Seems in nice condition, and cheap enough.
Will be a while before it gets here, and fingers crossed it works. From seller's description that's not guaranteed.
Just so long as that tiny gold plated unobtainium varactor is OK.


This also happened with ICs and IC sockets although in this case it may have been helped along by those cheap edge wipe sockets Texas Instruments made which were unusually unreliable.

Arrgh! Those damned TI sockets... how I hated them. How did TI manage to make anything so flakey? I never could decide if it was mainly due to the very weak and stretchy spring contacts, or the plating which seemed to become non-conductive.
Before learning about those, I once made the mistake of constructing a fairly complex prototype board with them, and point to point soldered kynar wire. Urrrgh...
After that I always used Augat machined pin sockets. Expensive, but they never failed.
« Last Edit: December 09, 2014, 09:03:14 am by TerraHertz »
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Offline David Hess

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #34 on: December 13, 2014, 01:42:00 pm »
Yay! Got one! Ebay 151502733003. Seems in nice condition, and cheap enough.
Will be a while before it gets here, and fingers crossed it works. From seller's description that's not guaranteed.
Just so long as that tiny gold plated unobtainium varactor is OK.

With some diagnostic work, the varactor can be replaced with a modern surface mount one.

Quote
This also happened with ICs and IC sockets although in this case it may have been helped along by those cheap edge wipe sockets Texas Instruments made which were unusually unreliable.

Arrgh! Those damned TI sockets... how I hated them. How did TI manage to make anything so flakey?

TI has a history of making mistakes like this and then ignoring or covering them up.  I try to avoid their products.

Quote
Before learning about those, I once made the mistake of constructing a fairly complex prototype board with them, and point to point soldered kynar wire. Urrrgh...
After that I always used Augat machined pin sockets. Expensive, but they never failed.

I like the machined pin sockets for repair work because if I am expending that much effort, then I only want to do it once.  I like cutting the pins out of the socket and mounting them individually as shown in the attached photo.
 

Offline TerraHertz

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #35 on: December 14, 2014, 09:40:29 am »
Yes, looks nice and you can see the tracks. I did the same thing a few times, I recall.
Needs something plugged into them to hold them in line for soldering.
Those other sockets are the offending items, aren't they? Are you replacing them all?

Ha ha, and the same people that chose those sockets for that board thought it was OK to alternate the orientation of ICs.

I spy tantalums. Together with *those* sockets I bet that board was soooo reliable.

Edit: PS I should have the 2901 in about 3 days.
« Last Edit: December 14, 2014, 09:44:00 am by TerraHertz »
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Online BravoVTopic starter

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #36 on: December 14, 2014, 09:55:20 am »
Edit: PS I should have the 2901 in about 3 days.

Please, it its not too troublesome, do a detail macro shots as well, especially if you spotted there are differences vs mine, thanks in advance.  :-+

Offline TerraHertz

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #37 on: December 14, 2014, 10:06:43 am »
Please, it its not too troublesome, do a detail macro shots as well, especially if you spotted there are differences vs mine, thanks in advance.  :-+

Sure, I was intending to. Though, just yesterday my camera lens (Canon) developed a problem. So now I have two Canon bodies (EOS 20D & EOS 40D) but no fully functional lens. Not sure how long that will take to fix.

The http://w140.com/tekwiki/wiki/2901  page could do with a lot better info.
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Offline David Hess

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #38 on: December 20, 2014, 12:47:04 am »
Yes, looks nice and you can see the tracks. I did the same thing a few times, I recall.
Needs something plugged into them to hold them in line for soldering.

No, I just friction fit them and solder from the top if necessary.  You have to be very careful about plugging something in to hold them because if it is tin plated, the tin will melt during soldering and fuse it into the socket.

Quote
Those other sockets are the offending items, aren't they? Are you replacing them all?

They are but the ones I replaced were used for ceramic packaged 723 regulators which ran hot and the heat caused the sockets to become loose.  There was not an actual failure but I did not like it.

Quote
Ha ha, and the same people that chose those sockets for that board thought it was OK to alternate the orientation of ICs.

That does not bother me.  I am sure they did that to make the layout easier.

Quote
I spy tantalums. Together with *those* sockets I bet that board was soooo reliable.

It is a Tektronix DC505 universal counter.  It had some bad transistors and a design flaw but none of the solid tantalum capacitors failed.
 

Offline TerraHertz

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #39 on: December 20, 2014, 03:16:39 pm »
Here's the teardown and repair of my Tek 2901.
  http://everist.org/NobLog/20141220_Tek_2901_teardown.htm
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Offline robrenz

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Offline extide

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #41 on: December 23, 2014, 06:55:34 pm »
Can someone point out what pic this rare diode is in and where it is located? I am trying to find what you guys are talking about...
 

Offline SeanB

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #42 on: December 23, 2014, 07:22:22 pm »
http://everist.org/NobLog/pics/20141220/05_9163_top_close.jpg

See the little clip between the 3 open core inductors at the bottom. That is the clip and the tiny gold button under it is the varactor in question.

At least is is possible to replace that, try getting a tunnel diode or even worse a backwards diode. Noone dopes a zener diode that heavily any more, you would have to use pieces of zone refining ends to get silicon that heavily doped.
 

Offline extide

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #43 on: December 23, 2014, 08:15:46 pm »
Ah, ok, I had seen that but didn't think it was it, heh. Thanks!
 

Online BravoVTopic starter

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #44 on: December 24, 2014, 03:56:24 am »
Here's the teardown and repair of my Tek 2901.
  http://everist.org/NobLog/20141220_Tek_2901_teardown.htm

Very nice  :-+

+1  :-+ :clap: , thanks, looking forward to see you fix the other problems as well.

Online BravoVTopic starter

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #45 on: December 24, 2014, 03:57:56 am »
Ah, ok, I had seen that but didn't think it was it, heh. Thanks!
This one has better view as in one of my photoshoot.

« Last Edit: December 24, 2014, 04:07:43 am by BravoV »
 

Online Alex Eisenhut

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #46 on: December 24, 2014, 04:32:09 am »
It's so small you'd hardly miss it if you put it in an envelope and mail it to me.
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Offline SeanB

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #47 on: December 24, 2014, 05:27:27 am »
It would probably fall out of the envelope though, unless you tape it to a card.
 

Offline Docholiday

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #48 on: February 26, 2015, 09:20:35 pm »
I was fortunate to come across one today. But there are two issues, one is the power switch and then the power indicator which I guess is incandesent? Anyway is it possible to replace both by just removing bottom cover?

Thanks,

Nicholas
 

Offline SAUL BRITTO

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Re: Tektronix 2901 Time Mark Generator Tear Down & Inspection
« Reply #49 on: March 08, 2016, 06:04:18 am »
I am a new owner of a 2901, hope it correspond to specs.There are some people are having problems with
A heater and a crystal inside it,do you see any problem in your unit around this?
Thank You, for all earth.
 


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