Tektronix 2465B oscilloscope teardown

[tggzzz]

Since it is not mentioned, the question would of course be what was the highest frequency (or fastest pulse width) used as comparison between ch1 and ch2 performance. I bet it was not anywhere near to about 100MHz where you would  expect the leads of the resistors to start playing a part by adding inductance.

The pulse width and pulse frequency are irrelevant. The only parameter that matters is the transition time (i.e. risetime/falltime). The only advantage of a higher pulse frequency on a non-digitising scope is that the higher the pulse frequency the brighter a trace will appear. For simple theory and illustrative measurements, see https://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/

For a 2465B, the pulse risetime should be <1ns, and the pulse frequency can be anything above, say, 100kHz. Obviously the scope bandwidth shouldn't be 20MHz, and the internal 50ohm termination should be used

But we can make some wild guesses, from looking at the picture...

It appears that the 50ohm termination resistor (the one that fails if too high a voltage is applied in 50ohm mode) has been replaced by two 68ohm resistors in parallel, i.e. 34ohms. That would be a very poor termination; the VSWR would be very high.

That would be a very long SMD resistor, let's guess 10mm. The inductance of a 10*4*1mm wire is 4nH. https://chemandy.com/calculators/flat-wire-inductor-calculator.htm

The inductance of a 10mm long 0.5mm diameter wire is around 7.2nH (the rule of thumb is 0.8nH/mm) https://chemandy.com/calculators/round-wire-inductance-calculator.htm Since there are two in parallel, the inductance would be around 3.5nH. The inductance of the resistor body is dependent on the construction, especially if the resistance is defined by a helical cut into a metal film. Hence the inductance of the through-hole resistors vs SMD resistor might or might not be a problem.

[Gregory]

The original resistor was not 50 ohm. It was very close do 34 ohm. The amplitude response is right on the mV level and the rise time is near 800ps



 

[tggzzz]

The original resistor was not 50 ohm. It was very close do 34 ohm. The amplitude response is right on the mV level and the rise time is near 800ps



 

Good news about the resistor value!

You cannot tell anything about the risetime from an avalanche pulse, since the trace is the conclusion of the input pulse and the scope's response. To find the scope's response it would be necessary to know input pulses shape and then mathematically perform the deconvolution.

Without that information and processing, the easiest technique is to have a step waveform with a rise time much shorter than the scope's rise time.

One technique for generating a step is to take an avalanche generator and add a parallel transmission line which is shorted at the other end. The line length determines the pulse width.

[Gregory]

I can't see why the avalanche pulse is not useful for bandwidth estimation.

Obviously that the trace will be the convoluted response of the pulse and the scope front-end, but the rise-time needs to be preserved in the perspective of a first-order bandwidth estimation. If the test avalanche impulse is fast enough, the dominant pole will be from the scope itself.

Unfortunately this is the fastest rising edge I can generate here in the lab and it's rise time is not far from the 2465B bandwidth
I measured it with a 1Ghz scope and it still measures ~800ps


But what I really think that matters is that the 2465B fixed channel 1 and original channel 2 still show exactly the same waveform, so it seems that the parasitics of the modification are not so important in for the bandwidth of this Tek...

Well..  I'm happy with the results and the purpose of my latest posts was to show that a burned Tek 24XX input module is not the end of the world hehehe

[tggzzz]

I can't see why the avalanche pulse is not useful for bandwidth estimation.

Obviously that the trace will be the convoluted response of the pulse and the scope front-end....

Here's a simple example from one of my scopes, illustrating why you need to accurately know the input waveform. My apologies for the poor picture.

The timebase is 1ns/div. What's the scope's bandwidth?

[AMR Labs]

I can't see why the avalanche pulse is not useful for bandwidth estimation.

Obviously that the trace will be the convoluted response of the pulse and the scope front-end, but the rise-time needs to be preserved in the perspective of a first-order bandwidth estimation. If the test avalanche impulse is fast enough, the dominant pole will be from the scope itself.

Unfortunately this is the fastest rising edge I can generate here in the lab and it's rise time is not far from the 2465B bandwidth
I measured it with a 1Ghz scope and it still measures ~800ps


But what I really think that matters is that the 2465B fixed channel 1 and original channel 2 still show exactly the same waveform, so it seems that the parasitics of the modification are not so important in for the bandwidth of this Tek...

Well..  I'm happy with the results and the purpose of my latest posts was to show that a burned Tek 24XX input module is not the end of the world hehehe

Sometime ago I also fell into the same misconception about measuring rise time that way with just a pulse, and was quickly put on the right track by another member. See bellow quote from his response message to me when I published my own "pulse" rise time results, very similar to yours. Since this exact explanation applies to your scenario as well I though it would be relevant to re-quote this response.

You can not measure rise time with an impulse. It can only be done with a step. The impulse can only show you the slew rate. The reason is simple: you never see the true "top" of the impulse before it begins decreasing in amplitude causing the scope response to follow. Therefore you can't set the 90% to anything meaningful. This is where the step is used; the top of the step eventually becomes clearly visible, so you can set the 90% mark against this 100% reference. Put another way, knowing that the trace is increasing is meaningless unless you know what point it is increasing toward.

My 2465A (350MHz) had a rise time to a very fast step (<50 ps rise time) of dead on 1.0 ns, and I had also measured the actual -3 dB point at about 375 MHz (using a leveled sine generator). It follows that a 400 MHz 2465B should be about 8.7 ns or so. The apparently significantly shorter response to your impulse generator is misleading and not accurate.

With that said, you can fairly easily convert an avalanche impulse generator to a step generator by substituting the capacitor for a short piece of 50 ohm coax, acting as a charge line. It needs only store a few ns of charge, so with 1 ns per 20 cm, you don't need much at all. (don't go too long, nor pulse too frequently as it stresses the transistor). A follow up Jim Williams app note builds upon his avalanche pulse (impulse) generator to make a step generator using coax as a charge line (AN94).

[Gregory]

Really nice !!

I'm back with pictures using the coax charge line



channel 1 with the thruhole resistor on the input attenuator and original channel 2

[AMR Labs]

 

Good job updating your impulse gen. So there seems to be after all no difference between ch1 and ch2 response.
Perhaps the function of the resistor you replaced is somehow not critical to the input response characteristics.
Interesting indeed.

Edit1: However, given BW = 0.35/T, your scope seems to only have a calculated bandwidth of about 236MHz, and since you have an "A" version 2465 you should rather be seeing a 350+ MHz bandwidth result.

Edit2: by looking again at your pictures, I am now seeing that for the ch1 measurement the top of the step is not properly aligned to the 100% mark, so that is causing a measurement error. You should try again while making sure both the 0% and 100% marks correspond to the bottom and top of the step.

[Gregory]

Thanks !

Yep.. maybe the pulse gen is not fast enough. Also, the signal seems to have a slow ramp before the fast rise, it's difficult to align it precisely.

Sweeping with a RF synth shows me a 3db knee of 430Meg if I remember it correctly

I don't have an attenuator to measure the pulse with my 1gig scope, the max vertical scale is too low =/

[AMR Labs]

Check my previous post, I think you made a measurement error on the ch1 side, as the top of the step is not properly aligned to the 100% mark. It seems ok on the ch2 measurement, but there should definitively be a difference between both channels once you measure both by properly aligning the step between 0% and 100%.

Also make sure that you position as accurately as possible the two time markers between the 10% and 90% marks on the scale and then read off the time.

[Gregory]

You are right, I messed this up!

I will try again but I think the results will still be very close.

Thanks !

[tggzzz]

Good upgrade! It does look as if the two channels are pretty much identical.

What is the type of resistor you uses; at these frequencies the devil is in the details. I presume they aren't wirewound

Don't become too obsessed with the exact bandwidth. The only purpose of a scope is to show the waveform's shape, and that is a combination of frequency and phase response. The BW=0.35/tr is only an approximation, and 0.35 is sometimes replaced by 0.4.

Finally, there is a b*****d on fleabay that "upgrades" 2445B to 2465B. The results are "imperfect", but he takes precautions to avoid having to refund money. See the TekScopes groups.io group for further information.

[bdunham7]

Does anyone know offhand how many layers there are on the mainboard of these scopes?  I have an otherwise nice 2465 that was 'drilled' and I'm considering whether to attempt a bodge repair or part it out.  I actually have two of these boards that have been drilled in two slightly different spots.  Apparently some corporation out there decided to drill all of their test equipment before selling it to the surplus (scrap) market. 

[AMR Labs]

Quite a few layers for sure, not sure exactly how many. Long shot, but if you look at the board edgewise that might give you a general clue if you manage to visualize the actual layers. A good place to ask this question where you are most likely get a good accurate answer is at the Tekscopes group. My bet is that it will be very though to fix the damage done by the drilling, as there might be severed connections that do not even surface to any above board component. But if you feel adventurous by all means go for it, we will certainly root for your success.

TekScopes Group:
https://groups.io/g/TekScopes

[MarkL]

Does anyone know offhand how many layers there are on the mainboard of these scopes?  I have an otherwise nice 2465 that was 'drilled' and I'm considering whether to attempt a bodge repair or part it out.  I actually have two of these boards that have been drilled in two slightly different spots.  Apparently some corporation out there decided to drill all of their test equipment before selling it to the surplus (scrap) market. 

Wow, that's a shame.

BravoV has photos showing it is a 4-layer board:

  https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1212961/#msg1212961

Why not give it a try?  You can't make the board any worse.  You could carefully excavate more of the surface around the hole on the top and bottom and see if you can expose any additional layers.  You should find at least a ground plane, which might not need any repair.

Looking at a 2445A A1 board, I can see traces on a second layer from the top, and none from the bottom.  So it might be, top to bottom: signal/power, signal/power, ground, signal/power.

EDIT: Another idea is to use a shallow counter-sink bit on the hole from one or both sides.  This would cut the PCB at an angle and make the copper layers more obvious.

[Kartika]

so guys
I am just about to reassembly on my vanilla 2445 after a full recap and I wanted to show off my custom U800 heatsink solution.  I'm pretty proud of it.
It seems pretty clear to me that Tektronix, at some point in the design process, contemplated a heatsink here given the mounting screws they included.  So I tried to make something close to what I imagined they had in mind.

Hi people
I want to present you my first prototype heatsink cooler for U800 IC chip that you may have in the future?
made on a CNC machine and the material is aluminium EN AW 6061.
This is not the final look. it will be completed soon
if anyone is interested let me know
Thanks. greeting

[AMR Labs]

OK here we go again, guess I'll chip in for this one. Anyone is of course free to do whatever they feel is best for their scope but please read this first...

As said quite a few times before, both here on this thread and also repeated by some very knowledgeable people close to Tektronix on the TekScopes group: the heatsink on U800 is completely unnecessary, of course as long as the normal internal flow is unimpeded by anything blocking either the intake or exhaust, and of course that the inside of the scope is not covered in dust or any other stuff that could affect the heat dissipation of the critical components. BTW U800 is just one of several delicate chips temperature wise that fully depend of a healthy airflow which again is easily achieved as long as nothing is blocked and the scope has a good working fan.

Fact is that the U800 chip is totally fine as-is, and as a matter of fact Tektronix had initially designed the board in order to accommodate a heatsink thinking it would be necessary but then after initial testing was done they noticed that the chip temperature was keeping well within the limits without it, so the heatsink idea was abandoned. This is the reason that there are those two threaded studs which where already incorporated into the board production. And since the heatsink was going to go under the chip, they put washers between the IC and the PC board simply to make up for the correct spacing as the chip pins can only be inserted so far into the holes on the board before hitting the limits while the IC bottom is still not firmly seated against the board. This IC is also very sensitive to overtightening and can easily be damaged by delamination of the actual die from the substrate, something that will certainly ruin your day.

The odds are really not in anyone's favor when disturbing a perfectly working chip that has been operating for decades, and that will continue to do so, against the risk of causing damage if you accidentally over tighten those studs, or even if one side is slightly torqued down tighter than the other could cause enough unbalance to create internal stress to break something. It really does not take much to reach that breaking point, and there is also the expansion of the component that has to be accounted for once the die starts to heat up during normal operation. And yet another well known problem, but that specifically applies to the glue-on type heatsinks, is that they often will come loose and fall off. This might obviously short out something inside, perhaps some other "unobtanium" part. So absolutely not wort the risk. If I where you, just leave it alone and enjoy your scope. Hope that helps.

Nice looking design, though.

[med6753]

Agree with AMR Labs 100%

1. Keep bottom vents clear at all times.

2. Don't stack the scope on top of another instrument that generates heat.

3. Insure the fan is operational.

4. Leave U800 alone. 

[Kartika]

Tektronix had initially designed the board in order to accommodate a heatsink thinking it would be necessary but then after initial testing was done they noticed that the chip temperature was keeping well within the limits without it, so the heatsink idea was abandoned.

This IC is also very sensitive to over tightening and can easily be damaged by decontamination of the actual die from the substrate, something that will certainly ruin your day.

or even if one side is slightly torqued down tighter than the other could cause enough unbalance to create internal stress to break something.

4. Leave U800 alone.

  - unacceptable 

Hi nice observation but you do not take cost-effectiveness, investment, programmed obsolescence, etc. if the factory meant absolute quality, then it would not install or produce a maxim IC chip that is structural unstable, etc. very bad also RIFA madness @ all! and a complete minimum investment / performance calculation for maximum profit.
the goal is to stop the temperature oscillation in order to make us lucky. we should achieve absolutely better cooling, with higher air flow, I found a great replacement.
p.s.
why they do not tell us how to, or build, make new U800.... i believe on market we heave 1000 units still operate... because of this IC all unit become trash permanently......
I am indignant because of that .. and then I wonder what ecology and consciousness is ...

PMD1208PKB1-A 90m3/h
fan dimesion 80x80x20mm

https://www.tme.com/ca/en/katalog/dc12v-fans_112524/?visible_params=2%2C173%2C181%2C2699%2C174%2C98%2C179%2C183%2C259%2C120%2C117%2C184%2C68%2C74%2C176%2C536%2C77%2C32%2C175%2C23%2C177%2C1774%2C2546%2C178%2C2190%2C1605%2C82&mapped_params=2%3A391%3B174%3A1439649%3B

Tektronix SUCKS!!!!!
Tektronix is trying to manipulate the oscilloscope market. Today I learned from
my local dealership that they are required by contract to destroy every scope
which is traded in for a new Tektronix scope, regardless of age or condition. So
if you decide to trade in that old scope for a Tektronix, know ahead of time
that it is NOT going to end up in the hands of a ham, or of some kid learning
and experimenting in electronics on a tight budget like I was thir... er, twenty
years ago. No, Tektronix needs to raise their profits by destroying every used
scope they can get their greedy little hands on, regardless of who feels the
pinch!
https://groups.google.com/g/rec.radio.amateur.homebrew/c/FfNSJ6Ho50k?pli=1

[tautech]

p.s.
why they do not tell us how to, or build, make new U800.... i believe on market we heave 1000 units still operate... because of this IC all unit become trash permanently......
I am indignant because of that .. and then I wonder what ecology and consciousness is ...

Google says otherwise:
https://www.eevblog.com/forum/testgear/tek-2400-scopes-have-the-schematics-for-the-modules-been-released/
https://www.davmar.org/TE/Tek2465/lafay.html

[Kartika]

The “inventor” never proceeded with his design.

[tautech]

The “inventor” never proceeded with his design.

Check the video in this thread:
https://www.eevblog.com/forum/testgear/tektronix-2400-series-scope-u800-replacement/

[AMR Labs]

Hi nice observation but you do not take cost-effectiveness, investment, programmed obsolescence, etc. if the factory meant absolute quality, then it would not install or produce a maxim IC chip that is structural unstable, etc. very bad also RIFA madness @ all! and a complete minimum investment / performance calculation for maximum profit.
the goal is to stop the temperature oscillation in order to make us lucky. we should achieve absolutely better cooling, with higher air flow, I found a great replacement.
p.s.
why they do not tell us how to, or build, make new U800.... i believe on market we heave 1000 units still operate... because of this IC all unit become trash permanently......
I am indignant because of that .. and then I wonder what ecology and consciousness is ...

PMD1208PKB1-A 90m3/h
fan dimesion 80x80x20mm

Tektronix SUCKS!!!!!
Tektronix is trying to manipulate the oscilloscope market. Today I learned from
----[snip]-----

Are we talking about present day tektronix, or when the 2465 scope was still being produced in the late 1980s? I cannot speak for present day, but back when it was certainly a different company with different values, professionalism, and  philosophy. Ask anyone that worked there back then.

RIFA cap failure = normal component aging, and that is well beyond its expected service life. Back then good quality part, probably one of the best given the technology at the time. Nothing to do with Tektronix trying to cut corners with lower quality components to save a few pennies. 30+ year cap subjected to spikes and surges almost every time the scope is operating. Also, back then there was not so much "dirt" on the AC mains. Perhaps rating it at a bit higher voltage margin then 275VAC (I think it is the cap rating) might have helped a bit stave off some degradation to coming close to short out when the scope is operated on 240V mains, but back then Tek figured it would be enough. And again 275V cap on a 240V line still sounds quite ok (its definitively far from blowing up) even today with a new off the shelve good quality AC rated capacitor. And besides Tek never thought that any scope would still be in use after more than three decades, mainly due to mandatory obsolescence rules in most of the companies that where buying these scopes. They never figured the fan base would still keep them alive after so long.

Fan failure = same 30+ years of service life, spinning and spinning.... Also there are two different types of fan depending on the scope version.

MAXIM chip (initial) problems = nothing to do with Tektronix. They sold the chip foundry to Maxim, and it took them a while to get things right so the great majority of the problematic chips where usually related the first few batches. After some time they figured out all the problems and chip production of later samples reliability was comparable to original in house Tek chip. Unfortunately Maxim chip got a bad reputation as a whole due to those early issues.

With all due respect, I think you need to get  your facts straight. I am not anywhere near at the level of Tektronix experience of some of the older guys, but I have read a lot over time, and quietly hung around this thread and at the TekScopes group, so have learned a lot by listening to the knowledgeable people over the past few years since I have been involved with Tek scopes, specially since I got my own 2465B and managed to get it working thanks in a big way due to the information contained in this thread starting from page 1. Perhaps you should try doing the same before trowing out opinions like these that seem to be a bit unfounded, or that perhaps rather apply to more recent times and not directly related to the 2465 family of scopes and what this thread is mostly about.

And please don't feel like I am trying to suppress in any way your opinions and comments. I don't even consider myself to be one of the long time members here, very far from it, but in general I feel everyone here enjoys having these conversations from time to time and learning about other people's experiences and opinions about Tek scopes in general. But at the same time on the other hand we also try to educate people based on facts and hopefully give them some new knowledge and perspective. So please carry on and keep up this discussion alive for as long as you think it will be in your interest to do so.

EDIT: to correct spelling.

[mawyatt]

AMR,

Agree these 2465 scopes are living well beyond anyones expectations. I have 2 and repaired both, neither has a heatsink on U800, also replaced the electrolytic caps and infamous RIFA types.

How is a manufacture supposed to know a cap type will fail after 30~40 years, as all they can do is the classic high temperature "life test" within a reasonable time frame.

I've used Tektronix and HP equipment my entire career (retired now), and probably purchased over $1M total. Every instrument with the exception of 1 HP generator that was supposed to replace the HP3325, was well designed and constructed and no apparent cutting corners to save a few $, and performed well beyond the specs and the "Intended Spec Use". If anything, they all were well over-designed, and you could bet your career on the results they produced.

The ISU was a very important part of the older Tektronix and HP equipment DNA, they were designed to make complex and accurate measurements, and not just meet some specs for a Product Brochure. Others had equipment that they touted as Better than HP or Tek on some spec, but in actual use were often not up to the task because of inferior ISU..

To bash the older Tek and HP equipment is an insult to the best engineered equipment at the time, and the very foundation for all the nice equipment options we have today IMO.

My two old Tek 2465 scopes still perform (as do my old HP 34401As) and I just used one to verify the output of a new AWG squarewave and compared against my new SDS2102X Plus DSO, they both agree quite well, not bad for a 35 year old scope

Best,

[Kartika]

"dirt" on the AC mains. Perhaps rating it at a bit higher voltage margin then 275VAC (I think it is the cap rating) might have helped a bit stave off some degradation to coming close to short out when the scope is operated on 240V mains, but back then Tek figured it would be enough. And again 275V cap on a 240V line still sounds quite ok (its definitively far from blowing up) even today with a new off the shelve good quality AC rated capacitor.

then or now, it is desirable to have prevention EMI filter and Insulation trasfomator.

question
has any of you had a chance to see the military version .. i think it has a cooling u800

Alan thank you for expressing your opinion, peace
Regards