Author Topic: Tektronix 2465B oscilloscope teardown  (Read 224841 times)

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Offline BravoV

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U800 chips and A1 board layers view
« Reply #925 on: May 20, 2017, 04:07:59 AM »
Mined some gems lately ....  :-DD

I just leave these few close up shots here, hopefully will aid someone, someday that who want to desolder, replace or do some surgery at their U800 gem chip or A1 board repair.

Minor notes, from the cut view, A1 board is clearly a 4 layers board.
« Last Edit: May 20, 2017, 04:32:12 AM by BravoV »
 

Offline med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #926 on: May 20, 2017, 04:45:32 AM »
Obviously you have some junk units laying around. By any chance do you have a 2465 Buffer board with Option 01 (DMM) and any combo of options 06, 09, 10? Tek P/N 670-7830-05 or 670-7830-09. I'd salvage the EAROM off it to try to fix a checksum error on mine.

Probably not...it's not very common but I figured I'd ask.  :-+ 
« Last Edit: May 20, 2017, 04:49:22 AM by med6753 »
 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #927 on: May 20, 2017, 10:06:42 PM »
Obviously you have some junk units laying around. By any chance do you have a 2465 Buffer board with Option 01 (DMM) and any combo of options 06, 09, 10? Tek P/N 670-7830-05 or 670-7830-09. I'd salvage the EAROM off it to try to fix a checksum error on mine.

Probably not...it's not very common but I figured I'd ask.  :-+

Wish I have that, sorry.  :-//

No, I'm not the one who butchered those A1 boards, no way in hell I would do that.  :'(

Actually they're sort of "souvenir" gift from a friend who visited abroad, and brought me these as he aware of the U800 obsession, at least me as a 2465B owner.  :palm:

Offline med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #928 on: May 21, 2017, 03:05:45 AM »
Obviously you have some junk units laying around. By any chance do you have a 2465 Buffer board with Option 01 (DMM) and any combo of options 06, 09, 10? Tek P/N 670-7830-05 or 670-7830-09. I'd salvage the EAROM off it to try to fix a checksum error on mine.

Probably not...it's not very common but I figured I'd ask.  :-+

Wish I have that, sorry.  :-//

No, I'm not the one who butchered those A1 boards, no way in hell I would do that.  :'(

Actually they're sort of "souvenir" gift from a friend who visited abroad, and brought me these as he aware of the U800 obsession, at least me as a 2465B owner.  :palm:

No problem, appreciate the response. I've been experimenting with different schemes in an attempt to fix the checksum error. One experiment was to provide standby power to the EAROM when the scope is powered off. It was partially successful in that I was able to get the scope to pass all tests consistently upwards of 6 hours rather than for approx 10 minutes after performing the DC balance check which clears the checksum in both the A5 board and the Buffer board. But it was inconsistent. Sometimes it wouldn't clear at all.

As I've mentioned in prior entries in this thread I've noticed no negative effects with the checksum problem on the Buffer board. It clears when I press the A/B/Menu switch. And the DMM and Counter options calibrated with no issues. It's just a minor annoyance.

I keep an eye on E-bay but so far nothing has shown up.     
 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #929 on: May 21, 2017, 03:13:59 AM »
Yeah, those option boards alone are rare as hen's teeth as Dave said, wish you good luck.  :-+

Online SeanB

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Re: Tektronix 2465B oscilloscope teardown
« Reply #930 on: May 22, 2017, 05:32:55 AM »
At least with the sawn board you can be sure the U800 is not a fake chip with more certainty, but the bigger question is if they work still, and if not if they are repairable with new package and leadwires after they are decapped.
 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #931 on: May 22, 2017, 06:49:40 PM »
At least with the sawn board you can be sure the U800 is not a fake chip with more certainty, but the bigger question is if they work still, and if not if they are repairable with new package and leadwires after they are decapped.

Yep, I'm curious too, its just my current U800 is working fine.

Offline BravoV

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Tektronix U800 Pads
« Reply #932 on: May 22, 2017, 06:53:55 PM »
More on the U800 pads and traces as references.

Beware these two photos are in original size, and managed to manually adjust their compression level up to the forum limitation while still have enough details (1 MB each and 2MB total max per post).  >:D

PS : Pardon for few lints as I was running out of lint free wiper.   :P
« Last Edit: May 22, 2017, 07:25:44 PM by BravoV »
 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #933 on: May 22, 2017, 06:59:15 PM »
Another proof that the U800 cooling design is sort of half baked  ::), the two star rings basically lift the whole IC from the big cooling pad below it, and the only cooling path only thru the other rings at the tab (not pictured here).  :palm:

Second shot is the close up of U800 ( Tektronix 155 0241 02 ) bottom (this is Maxim's one) , the chip die location is obvious.
« Last Edit: May 22, 2017, 07:38:02 PM by BravoV »
 

Offline David Hess

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Re: Tektronix 2465B oscilloscope teardown
« Reply #934 on: May 22, 2017, 09:21:01 PM »
When I saw how Tektronix mounted these parts, I concluded that somewhere they screwed up the engineering.  The shoulder of the pins prevents the DIPs from sitting flush and even if they did not, DIP leads do not allow enough strain relief for good reliability.  DIP packages designed for heat sink attachment have a very different configuration.  What I think might have worked is a thermally conductive spacer between the package and the board and the right kind of low profile collet socket.

Maybe what they did was sufficient though.  What was the failure rate for these parts while under warranty?
 

Online grumpydoc

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Re: Tektronix 2465B oscilloscope teardown
« Reply #935 on: May 22, 2017, 09:28:39 PM »
When I saw how Tektronix mounted these parts, I concluded that somewhere they screwed up the engineering.  The shoulder of the pins prevents the DIPs from sitting flush and even if they did not, DIP leads do not allow enough strain relief for good reliability.  DIP packages designed for heat sink attachment have a very different configuration.  What I think might have worked is a thermally conductive spacer between the package and the board and the right kind of low profile collet socket.

Maybe what they did was sufficient though.  What was the failure rate for these parts while under warranty?
I read somewhere that the original intent was to have the tab in contact with the PCB to provide heatsinking but this didn't work given the stand-off provided by the DIP leads.

Has anyone tried thermal pads under U800?
 

Offline David Hess

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Re: Tektronix 2465B oscilloscope teardown
« Reply #936 on: May 22, 2017, 09:48:03 PM »
When I saw how Tektronix mounted these parts, I concluded that somewhere they screwed up the engineering.  The shoulder of the pins prevents the DIPs from sitting flush and even if they did not, DIP leads do not allow enough strain relief for good reliability.  DIP packages designed for heat sink attachment have a very different configuration.  What I think might have worked is a thermally conductive spacer between the package and the board and the right kind of low profile collet socket.

Maybe what they did was sufficient though.  What was the failure rate for these parts while under warranty?

I read somewhere that the original intent was to have the tab in contact with the PCB to provide heatsinking but this didn't work given the stand-off provided by the DIP leads.

Has anyone tried thermal pads under U800?

The funny part though is that they did not even try this.  Using lockwashers as spacers is the last thing I would have considered.

One of the common problems with flange mounted packages is that the base gets bent with the ends being pulled down and any thermal compound pushing up in the center which breaks the die attachment.  This would go double for a narrow DIP package with the fasteners at the ends and its relatively thin base.

The solution is to use a clip which pushes down on the center of the package but that would have worked poorly in this case because of the soldered DIP leads holding the package rigidly in place.  Still, I think it would have been better than the lockwashers although they would have needed to find another way to electrically attach the tabs.
 

Offline med6753

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Re: Tektronix 2465B oscilloscope teardown
« Reply #937 on: May 23, 2017, 02:55:09 PM »
While I agree that the U800 is an unorthodox and possibly flawed design I suspect that the root cause of many failures is improper maintenance of the cooling system. I've done several checks and experiments on the 2465 cooling system design to understand how it functions for reasons that I'll explain later. Here is some of what I've found:

It is important that the ventilation slots on the bottom of the case be kept clear. Those slots are more or less directly below U800. I performed an experiment with smoke to gauge the amount of air drawn into those slots by the cooling fan and it is considerable. For maximum effectiveness I would recommend that the scope always be up on the tilt bail rather than down on it's feet. And certainly not stacked with other hot equipment below it.

Directly in front of the bottom ventilation slots there is a large black heatsink bonded to the outside of the case. This may be a feature of only fully optioned 2465's with the DMM and Counter. I'm not sure. You guys who have non-optioned 2465's would have to chime in. But I did see a 2465 DMS for sale on E-bay where the heatsink was missing and you could clearly see that it was once there.

I wanted to get an idea of how warm the rear metal panel got after several hours operation. So I attached a thermocouple to the panel just opposite the power supply. I applied a 1ns rise time 1Mhz square wave to channel 1 to give the sweep circuits a good workout. The results in the following picture. After 2 hours the temperature rose from 72 degrees F ambient to 97 degrees F and stabilized and rose no higher. Not bad.



The most important part of the cooling system is the fan itself. The 2465 uses a Siemens hall effect sensor motor with a squirrel cage impeller (See pix).  The 2465A and B use a more conventional computer type fan which is easy to service.       

Rear plastic panel removed to show impeller


The Siemens motor is prone to develop screeches and rattles over time. There is a rebuild procedure to install new bushings that is ridiculously complex due to the design of the motor. And replacement motors are unobtainium. See this link for the rebuild procedure.

http://antiqueradios.com/forums/viewtopic.php?f=8&t=235478

My Siemens motor does have a loud rattle. But luckily only for about 20 minutes after power on then it settles down and is whisper quiet. For now it's going to remain in place but I'm sure one of these days it's going to crap out. So I have designed and built a replacement fan assembly ready to install should that happen. It uses a conventional 80 x 80 fan and will totally replace the Siemens assembly. This is the reason for performing the above measurements. It's a set of baseline data that I can use to make appropriate adjustments if I have to install the new fan.

If anyone is interested in seeing the replacement fan design let me know and I'll post it. 
« Last Edit: July 18, 2017, 12:44:39 PM by med6753 »
 

Offline Ed Bray

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Re: Tektronix 2465B oscilloscope teardown
« Reply #938 on: July 18, 2017, 05:58:55 AM »
I bought a 2455B today on ebay, it will arrive tomorrow, there does not seem to be a lot about this model, loads about the 2445B and 2465B.

Got it for a good price (£124 delivered) so hopefully it is not a anchor, the seller states he will take returns so if it does turn out to be bad I'll only lose the shipping costs.
 

Offline BravoV

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Re: Tektronix 2465B oscilloscope teardown
« Reply #939 on: July 18, 2017, 10:06:37 AM »
Welcome aboard and also to the forum Ed.

Yeah, that model is rarely seen in the wild, please share few of it's internal photo shoots during your inspection teardown.

Offline Ed Bray

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Re: Tektronix 2465B oscilloscope teardown
« Reply #940 on: July 19, 2017, 01:47:43 AM »
Thanks for the welcome.

The 2455B arrived this afternoon and although it powers up and seems to go through a startup regime there is nothing on the CRT. No trace, no display, nada!

So it's already back in its packaging waiting to be collected for it's journey back. Ah well, back to my IWATSU.
 


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