Tektronix 2465B oscilloscope teardown

[BravoV]

Mined some gems lately .... 

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.

[med6753]

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.   

[BravoV]

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. 

[med6753]

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. 

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.     

[BravoV]

Yeah, those option boards alone are rare as hen's teeth as Dave said, wish you good luck. 

[SeanB]

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.

[BravoV]

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.

[BravoV]

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). 

PS : Pardon for few lints as I was running out of lint free wiper.   

[BravoV]

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). 

Second shot is the close up of U800 ( Tektronix 155 0241 02 ) bottom (this is Maxim's one) , the chip die location is obvious.

[David Hess]

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?

[grumpydoc]

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?

[David Hess]

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.

[med6753]

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. 

[Ed Bray]

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.

[BravoV]

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.

[Ed Bray]

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.

[USMC_Spike]

My 2465a is not so pristine.
I will be reading intently for some time.

Thank you.

USMC_Spike

[cvavr]

Hello

It is my first post on this forum.
Just bought an old 2467 on ebay and now I am thinking on upgrading it with option 06 CTT.
I have found an A20 670-7830-13 buffer board and an A27 670-7997-01 CTT board.
The problem is that the 2467 requires an A27 670-7997-07 or A27 670-7997-09 CTT board.
The 670-7997-01 is for the 2465. The 2467 is similar to the 2465A.
Looking at the schematics of both -01 and -07 I've notticed that they are identical.
So most likely the difference is the firmware in the U5930 EPROM.
Maybe somebody has the binary image of the U5930 for the CTT boards A27 670-7997-07 or A27 670-7997-09.
Many thanks in advance.

[WastelandTek]

Whelp, I just got gifted a vanilla 2445, thankfully in relatively good working order.  There does seem to be something a little wonky in the input coupling relays.  looks like I have some work ahead of me curating this.  Only just started reading but just with a cursory assay of the literature;

>electrolytic and some film caps

>some resistors

>heatsink U800

>construct interface and read out cal data

>develop strategy for eventual memory replacement and reprogramming

>keep eye out for later model rear panel to facilitate eventual fan replacement

have I missed anything obvious?

[tggzzz]

Whelp, I just got gifted a vanilla 2445, thankfully in relatively good working order.  There does seem to be something a little wonky in the input coupling relays.  looks like I have some work ahead of me curating this.  Only just started reading but just with a cursory assay of the literature;

>electrolytic and some film caps

The mains input filter caps, definitely. http://www.condoraudio.com/wp-content/uploads/Projects/Tektronix-2465B-Oscilloscope-Restoration-Repair.pdf

Otherwise I suggest only as necessary (i.e. short circuit tants or too much ripple on voltage rails). Depending on whether you have a 2445/2445a/2445b, it may be beneficial to replace some SMD electrolytics on the control board.

>heatsink U800

Opinions vary. Be aware some say that it is easy to mechanically damage the IC when fitting a heatsink. I suggest not touching it until necessary.

>construct interface and read out cal data
>develop strategy for eventual memory replacement and reprogramming

My technique is to make a video of the screen while using the screen controls to step through the memory. Make sure you can read all the values, and store the video safely.

If/when a problem occurs, transcribe the memory contents. My plan with my 2465 or 2455B is then to create a replacement for whatever memory has become deceased, probably using an arduino-class MCU and programming to with bit-banged i/o simulating the real memory. Obviously I haven't done that, so the feasibility is unproven.

Don't forget to run the self-tests detailed in the manual.

[Knack]

I have just pulled my 2465B out of storage to use it after almost 30 years. I had forgotten that I even had it. As I was the original purchaser and the only user, I know when I last used it, it worked flawlessly.

So I am in the process of getting her cleaned up a bit before hitting the on button. I have 4 of the original probes, 2 of which are still in the factory sealed pouches. Plus the ops manual, the Polaroid camera shroud, and the added reticules.

I'll love getting her back to operating condition. Thanks for starting this thread, it will come in handy.

[med6753]

I have just pulled my 2465B out of storage to use it after almost 30 years. I had forgotten that I even had it. As I was the original purchaser and the only user, I know when I last used it, it worked flawlessly.

So I am in the process of getting her cleaned up a bit before hitting the on button. I have 4 of the original probes, 2 of which are still in the factory sealed pouches. Plus the ops manual, the Polaroid camera shroud, and the added reticules.

I'll love getting her back to operating condition. Thanks for starting this thread, it will come in handy.

Looking forward to see it awake from it's long Rip Van Winkle slumber. Post pictures! 

And welcome to the forum! 

[Knack]

Thanks med, will do. 

[tazdog]

All:
This has been a very informative thread with lots of good information and I was wondering if anyone has had this issue...

I purchased my 2465B from eBay with a known issue thinking that it could be fixed with the "known issue fixes" in this thread but not yet. 
I received it with Tektronix cal stickers in place so I thought "BONUS! no one has tinkered with it". So I went through the normal procedures and replaced PS caps and A5 board caps and carefully cleaned the electrolytic mess made by those. I also replaced the cal RAM. Then I noticed that the CAL/NO CAL jumper was in the CAL position?? Being a noob with the 2465 I didn't realize that the bottom row displayed "..." between settings. Why was it in the CAL position?? The only explanation is that someone sent the scope to TEK for repair and for one reason or another the customer didn't want it fixed. So TEK sent the scope back with CAL in place that way it could still be used albeit in a limited fashion.

So, what is the issue I hear you say??...

The scope will not DC balance on ch 1 & 2. Auto DC BAL routine (pressing both upper coupling buttons of CHs 1 & 2 simultaneously) does not balance the channels. You can flip through the input level settings and the trace moves all over the place.

Things that I have looked at...

1. After initiating the procedure and it completes there are no LIMIT errors.
2. Checking the Trigger pick-off of both ch. 1 and 2 during the procedure I see the scope has initiated +/- voltage switching of various potentials and i believe then the processor checks the TSO for when the Display Sequencer detects a trigger and I do see activity on this line. TLA of U500 goes to a high level but TLB shows a ramp so I think the processor is using this to detect the trigger level for the procedure.
3. If I use some of the the CAL data files uploaded to this thread and burn them to my RAM, the DC balance is close to what it needs to be but as soon as I run the DC balance procedure it goes right back to being bad.

Maybe I'm just 

Any Thoughts???

[tazdog]

Ok in case anyone is still interested I found the issue. The unit has a bad A&B Trigger chip - 155-0239-02