Author Topic: Tektronix 2465B oscilloscope teardown  (Read 475460 times)

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Offline David Hess

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1375 on: December 31, 2018, 04:08:13 pm »
What I do not understand is why they did not put a thermally conductive spacer under U800 before soldering it down.  Was it too much trouble on an otherwise automated manufacturing processed?
 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1376 on: December 31, 2018, 04:13:26 pm »
What I do not understand is why they did not put a thermally conductive spacer under U800 before soldering it down.  Was it too much trouble on an otherwise automated manufacturing processed?

Back at those era, did non metallic thermal pad was still not very good ?  :-//

Also the gap is quite large.
« Last Edit: December 31, 2018, 04:52:58 pm by BravoV »
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1377 on: December 31, 2018, 05:46:10 pm »
What I do not understand is why they did not put a thermally conductive spacer under U800 before soldering it down.  Was it too much trouble on an otherwise automated manufacturing processed?

From the TekIO group message I posted a few posts ago should clarify your question:

===========================================================
START PARTIAL QUOTE FROM https://groups.io/g/TekScopes/message/152372
===========================================================

...

"The engineer that designed U800 was excessively cautious,
and overestimated the heat that would be generated by his
new IC. When it came back from fab, he found that it did
*NOT* need any heat sinking to meet the full +50C design
temperature rating of the brand new 2465 scopes. So, the
heat sink was left off of the board."

...

===========================================================
END PARTIAL QUOTE FROM https://groups.io/g/TekScopes/message/152372
===========================================================
 

Offline David Hess

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1378 on: December 31, 2018, 05:50:29 pm »
But he underestimated the strain placed on the package by the mounting solution he ended up using.

What I do not understand is why they did not put a thermally conductive spacer under U800 before soldering it down.  Was it too much trouble on an otherwise automated manufacturing processed?

Back at those era, did non metallic thermal pad was still not very good ?  :-//

Also the gap is quite large.

Alumina and Kapton were readily available.  I have alumina spacers which are older than the 2465 series.
« Last Edit: December 31, 2018, 05:52:21 pm by David Hess »
 

Online med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1379 on: December 31, 2018, 05:55:21 pm »
Related to the U800 discussion. I conducted some experiments with the 24XX cooling system with these results and observations...

https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1215559/#msg1215559

And....ALL 24XX scopes should have the black heatsink bonded to the front bottom of the case. If it's missing you could have issues.   
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Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1380 on: December 31, 2018, 05:57:21 pm »
(Thought experiment: when was the last time you operated
your 2465 at 50C?)

Other than us Australian's without aircon.  :P

It is NOT very fun working on electronics (or electrical) stuff with sweat dripping down your arms and everywhere else into your tools and whatever you are working on. I know very well from working on boat electronics in the Caribbean when in the summer sometimes the inside temp in the cheapo customer sailing boats temps rise to the 35-40 deg C range with +90% humidity, specially if in a yard and out of the water. If I don't happen to have AC power to run my work fan the sweat taps really open big time!

 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1381 on: December 31, 2018, 05:58:30 pm »
But he underestimated the strain placed on the package by the mounting solution he ended up using.

+1 , thats the main problem that I see.

Even the two nuts were mildly fastened enough, there is no guarantee those two star washers will be the exact height to fill the gap underneath the chip, without stressing the embedded metal tab inside the chip, which is also will create the another strain vs the soldered pins.

Wonder if the stressed metal tab will affect the attached silicon die inside the chip, as the whole chip body + washers + nuts + soldered pins went thru so many thermal cycles and thermal expansion and contraction physically.  :-//

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1382 on: December 31, 2018, 06:05:51 pm »
Related to the U800 discussion. I conducted some experiments with the 24XX cooling system with these results and observations...

https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1215559/#msg1215559

And....ALL 24XX scopes should have the black heatsink bonded to the front bottom of the case. If it's missing you could have issues.

Hi med,

Do you by any chance have pics of that heatsink you mention? Did not see any pics of it on your post, not 100% sure where to exactly look for so as usual always would be nice to have one or two pics if you happen to have them. Thanks!
 

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1383 on: December 31, 2018, 06:17:35 pm »
But he underestimated the strain placed on the package by the mounting solution he ended up using.

+1 , thats the main problem that I see.

Even the two nuts were mildly fastened enough, there is no guarantee those two star washers will be the exact height to fill the gap underneath the chip, without stressing the embedded metal tab inside the chip, which is also will create the another strain vs the soldered pins.

Wonder if the stressed metal tab will affect the attached silicon die inside the chip, as the whole chip body + washers + nuts + soldered pins went thru so many thermal cycles and thermal expansion and contraction physically.  :-//

Also definitively a valid but again with all due respect <secondary> point unless one plans to mess with the mounting studs/nuts of U800. I thought we where mainly discussing the temperature issue of a <undisturbed> U800, which is what user DC1MC was initially inquiring about.
 

Offline David Hess

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1384 on: December 31, 2018, 06:22:46 pm »
Wonder if the stressed metal tab will affect the attached silicon die inside the chip, as the whole chip body + washers + nuts + soldered pins went thru so many thermal cycles and thermal expansion and contraction physically.  :-//

Strain in the lead frame absolutely affects reliability of the die attachment and it gets worse at higher temperatures and with more temperature cycles.  This is why the correct mounting of power packages is so important.  Motorola has a great application note discussing the issue.
« Last Edit: December 31, 2018, 06:27:15 pm by David Hess »
 
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Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1385 on: December 31, 2018, 06:26:49 pm »
Also definitively a valid but again with all due respect <secondary> point unless one plans to mess with the mounting studs/nuts of U800. I thought we where mainly discussing the temperature issue of a <undisturbed> U800, which is what user DC1MC was initially inquiring about.

Ok, fair enough, thanks for reminding, its just this issue pop out again in my head when every time this U800 discussion surfaced.

Also the two nuts of mine are gone, not used anymore when I realized while ago, the U800's of course.  :P

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1386 on: December 31, 2018, 06:29:38 pm »
Wonder if the stressed metal tab will affect the attached silicon die inside the chip, as the whole chip body + washers + nuts + soldered pins went thru so many thermal cycles and thermal expansion and contraction physically.  :-//

Strain in the lead frame absolutely affects reliability of the die attachment and it gets worse at higher temperatures and with more temperature cycles.  This is why the correct mounting of power packages is so important.  Motorola has a great application note discussing the issue.

Hi David, but just to be clear do you imply that there might be some mechanical strain already in place from the initial install/mounting of the U800 chip at the factory?
 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1387 on: December 31, 2018, 06:30:36 pm »
Wonder if the stressed metal tab will affect the attached silicon die inside the chip, as the whole chip body + washers + nuts + soldered pins went thru so many thermal cycles and thermal expansion and contraction physically.  :-//

Strain in the metal tab absolutely affects reliability of the die attachment and it gets worse at higher temperatures and with more temperature cycles.  This is why the correct mounting of power packages is so important.

Wonder this is related with the service of fixing the U800 chip provided years ago by 3rd party, which they sent the chip to a special shop in Japan to be re-heated if I'm not mistaken, and they claimed this fixed the common problem that was affecting this particular chip.

Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1388 on: December 31, 2018, 06:39:57 pm »
Also definitively a valid but again with all due respect <secondary> point unless one plans to mess with the mounting studs/nuts of U800. I thought we where mainly discussing the temperature issue of a <undisturbed> U800, which is what user DC1MC was initially inquiring about.

Ok, fair enough, thanks for reminding, its just this issue pop out again in my head when every time this U800 discussion surfaced.

Also the two nuts of mine are gone, not used anymore when I realized while ago, the U800's of course.  :P

All useful input in my view should always be more than welcomed, and definitively coming from this thread's originator. But I was just thinking in terms of keeping a proper sequence of QA's. Again, all relevant information to our 2465 scopes should always be posted specially taken into account the highly regarded reference status that this thread has achieved in the 2465 realm.

HAPPY -ALMOST- NEW YEAR!
 

Online med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1389 on: December 31, 2018, 08:24:02 pm »
Related to the U800 discussion. I conducted some experiments with the 24XX cooling system with these results and observations...

https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1215559/#msg1215559

And....ALL 24XX scopes should have the black heatsink bonded to the front bottom of the case. If it's missing you could have issues.

Hi med,

Do you by any chance have pics of that heatsink you mention? Did not see any pics of it on your post, not 100% sure where to exactly look for so as usual always would be nice to have one or two pics if you happen to have them. Thanks!

Here it is. But upon closer examination it's made of plastic. So now I'm not sure what it's intended function is.  :-// Both my 2465's have one.
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Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1390 on: December 31, 2018, 08:53:12 pm »
Never seen this on another 2465/x, and definitively not on my "B". Anyone else have input on this? Looks a bit weird being on the outside of the case, my two cents.
« Last Edit: December 31, 2018, 08:55:04 pm by AMR Labs »
 

Offline tggzzz

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1391 on: December 31, 2018, 09:41:26 pm »
Both my 2465s have it, my 2445B does not.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Satbeginner

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1392 on: December 31, 2018, 09:48:26 pm »
I have an 2465, a 2465A, a 2465ADM and two 2465B's.
None of them have such a thing....
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Offline AMR Labs

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1393 on: December 31, 2018, 09:55:10 pm »
If this "heatsink" is made out of plastic, can help but feel this is not something that came from the factory, specially being on the outside of the case seems outrageous for tek ------------------------------ ????

EDIT: I am really enjoying this fast pace posting back and forth!!


« Last Edit: December 31, 2018, 09:57:35 pm by AMR Labs »
 

Online med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1394 on: December 31, 2018, 10:21:08 pm »
I propose that the piece is there to insure airflow to the vents just behind it when the scope is down on it's feet. That's where U800 is located. That's the only thing that makes sense to me.

It's definitely a factory piece and I also suspect it's easily damaged and knocked off.
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Offline David Hess

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1395 on: January 01, 2019, 03:32:33 am »
Hi David, but just to be clear do you imply that there might be some mechanical strain already in place from the initial install/mounting of the U800 chip at the factory?

I am sure of it and that it was made worse by the high operating temperature and thermal cycling.  Those ICs (aren't they actually hybrids?) had poor reliability even before people started messing with them.  Maybe things could have been improved with a different die attachment material.

DIP package lead frames are pretty bad about this because all of the short pin connections leave very little mechanical compliance.  Some power DIPs had wide lead spacing or were used with a socket but more commonly the heat sink tabs were attached to the heat sink and not the board.

Wonder this is related with the service of fixing the U800 chip provided years ago by 3rd party, which they sent the chip to a special shop in Japan to be re-heated if I'm not mistaken, and they claimed this fixed the common problem that was affecting this particular chip.

Reheating melted the die attachment material reattaching the chip to the lead frame.
 

Offline tggzzz

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1396 on: January 01, 2019, 10:14:53 am »
I propose that the piece is there to insure airflow to the vents just behind it when the scope is down on it's feet. That's where U800 is located. That's the only thing that makes sense to me.

I've wondered that, and am partially convinced.

It isn't beneficial on a flat surface, but if there is paper underneath, it may ensure that the paper is not sucked upwards to block the vent. Another failure mode might be perching the scope on top of something that is narrower than the distance between the feet.

« Last Edit: January 01, 2019, 10:18:32 am by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1397 on: January 02, 2019, 07:13:30 am »
Wonder this is related with the service of fixing the U800 chip provided years ago by 3rd party, which they sent the chip to a special shop in Japan to be re-heated if I'm not mistaken, and they claimed this fixed the common problem that was affecting this particular chip.

Reheating melted the die attachment material reattaching the chip to the lead frame.

If that is the case, looking at the way U800 mounted here below at the IC front metal tab that is secured by a nut + two washers.



If thermal expansions or contractions happened at the two star washers and the fastened nut, and/or also the embedded bolt at the pcb. I guess this will stress out the whole IC's bottom metal tab, against the whole chip black plastic body, that is being held so firmly by the 24 soldered pins.

Not sure if this is the right terms, its like the metal tab is being peel off downward from the body.

Again, I'm just guessing and imagining this, as it may not be a problem at all.  :-//

Btw, the two nuts that are holding the U800 basically have minimal purpose as heat dissipation is not optimal thru the bolt, its not like the chip is going to fall down and detached from the PCB as its firmly held by 24 pins soldered at the PCB.
« Last Edit: January 02, 2019, 07:21:22 am by BravoV »
 

Offline mnementh

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1398 on: January 06, 2019, 02:25:11 am »
   

Latest from Tek on this issue (still ages ago, of course) is that U800 is not supposed to have two nuts on it; there was a TSB on it I remember from when I first started messing with them decades ago. After a certain Ser# they shipped with only one nut on the metal tab, and earlier models sent in for service would have the one not on the metal tab removed. They were also supposed to have the one nut on the tab retorqued to a lower tension in an effort to reduce this failure mode.

The above image is of a preventive maintenance mod based on that TSB, in which the IC is desoldered, socketed, and then reinstalled with a small heat sink/load spreader on the tab. IIRC, that is one of a number of mods performed by well-known eBay vendor 2465b on all his "Refurbished/Guaranteed" 24xx scopes.

I'm not exactly certain I believe that is a better approach than simply ensuring good thermal contact with the large copper fill directly under the IC, though all evidence I've seen on the subject indicates Tek deliberately placed these two star washers under the chip which clearly defeats any such heat sinking to that fill, and never reversed that design. My own gut reaction is that if I ever have reason to attempt such a service, I'll put some silicone thermal pads underneath the IC and shim the tab to eliminate any preload stress.

FWIW, none of the 3 2465s I own have that ribbed plastic/rubber/vinyl what-the-fuggever-it-is on the bottom front, though the suggestion that it serves to prevent occlusion of that most important vent over the U800 certainly sounds plausible. Possibly some vendor-added spacer for a 2465 that was assembled into/made part of a larger, special-purpose test gear?

mnem
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« Last Edit: January 06, 2019, 02:37:22 am by mnementh »
 

Online med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #1399 on: January 06, 2019, 08:02:56 am »
If there was a TSB for U800 and it's mounting it apparently wasn't known outside Tektronix. And as a side light how come no one, other than that one individual, produced one with that mod?

One of my 2465's was owned by IBM. IBM was very diligent about insuring their test equipment was up to snuff and had it's own instrument labs who's sole responsibility was repair/calibration. Only "tuff nuts" or unable to fix equipment was sent back to Tek which didn't happen very often. The U800 in this 2465 is untouched and the scope would have been back to the instrument lab on a yearly basis for a minimum a calibration. So I'm questioning the validity of this "TSB". IBM has bought literally thousands of instruments from Tek over the past 60 years so my thought in the interest of customer support this "TSB" would have been published and available.

And as another side light the last IBM internal instrument lab was disbanded about 2006 or so and all instrument repairs/calibrations are now contracted to outside cal labs.
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