I wonder why they used such a complex fan instead of just putting a muffin fan in the panel like practically every other instrument out there.
One thing I am nervous about though - this removal of the fan/mandrel. Are there any other tips anyone can give apart from 'go gently and glue back up if you have to'? I've read elsewhere that you can also push a bit on the mandrel, after loosening the nut a little. I also wondered about making some sort of jug to apply pressure in the right place. Can anyone give me advice or reassurance here?
Thanks a lot from the UK
Jon N
Your concern about the fan assembly is certainly understandable. If you apply pressure incorrectly you could break the fan itself. That would be a difficult repair.
I haven't heard about pushing the assembly forward slightly and I'm not sure if it would help because the mandrel is tapered. And all those years assembled has resulted in the fan and the mandrel "cold fusing" together. That's where the deoxit or some other penetrating oil would help. A long thin pair of needle nose pliers against the rear hub and carefully pry forward seems to be the best method that I found. The point is....don't be afraid of it....just work carefully and chances are it will come apart.
I wonder why they used such a complex fan instead of just putting a muffin fan in the panel like practically every other instrument out there.
Apparently some over zealous Tek engineer thought that the 2465 required a complex variable speed fan as shown in this schematic. And apparently later on it was discovered that a standard $20 computer type fan would do the job just as effectively.
It is similar how a bicycle steer is fixed.
To loosen: undo the nut a few turns, before any pulling!!, slightly tap the nut inwards, this will loosen the collet and the fan from the shaft.
Now pull the fan from the shaft.
To tighten: place the fan on the shaft, carefully tighten the nut. (A bit)
Here's the best picture I have of the fan removed. I was mistaken when I said you could pry from the back hub. You can't. The hub of the fan extends internal to the case. But the thin needle nose can get between the case and the shaft piece and carefully pull forward. What you call a mandrel and I call a collet you can barely see extending slightly out from the end of the fan. When you tighten the nut it pulls forward and compresses against the motor shaft and also tightens it against the fan itself.
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I was mistaken when I said you could pry from the back hub. You can't. The hub of the fan extends internal to the case.
But the thin needle nose can get between the case and the shaft piece and carefully pull forward.
To loosen: undo the nut a few turns, before any pulling!!, slightly tap the nut inwards, this will loosen the collet and the fan from the shaft.
Now pull the fan from the shaft.
Update - managed it!
Well, more or less. I packed some cardboard between the rear of the fan and the chassis, then got a small-ish hanner and tapped the screw head of the collet.
It took a bit more force than I was expecting but then it loosened and I was able to remove the fan.
The collet was still holding inside the fan assembly; I wanted to get it out and may have made a slight error there. I turned the collet and it started coming out; however now that I have it out I see that it has a break in the middle, just where the metal screw stops. I am guessing this is a common place for it to break; it is not all the way through and I am pretty confident that a bit of epoxy resin will hold it OK once I have degreased the thing.
So now I am on with the next stage. I just have to puzzle out how to remove the black plastic mains shield. That should be easy, but...
Cheers, J^n
Apparently some over zealous Tek engineer thought that the 2465 required a complex variable speed fan as shown in this schematic. And apparently later on it was discovered that a standard $20 computer type fan would do the job just as effectively.
Apparently some over zealous Tek engineer thought that the 2465 required a complex variable speed fan as shown in this schematic. And apparently later on it was discovered that a standard $20 computer type fan would do the job just as effectively.
I replaced the "complex variable speed fan" with a "$20 computer type fan" in my 2465 because the bearings were worn and the motor squealed like <insert wounded animal here>. After suffering this abomination for a couple of months, I took the trouble to find a NOS motor to reverse the mod. I'm also fortunate enough to own a 2467, so I've had occasion to compare the two kinds of fans.
So, from experience, the 2465 is as near silent as makes no difference - as is my 485, which has the same kind of fan. The 2467, by comparison, while perhaps not as loud as a 747 at takeoff, is annoyingly loud enough that it's only turned on at need.
All this to say that I take umbrage at the "do the job just as effectively" statement, and I'd wager you haven't had the opportunity to compare the two.
I'd also guess the squirrel cage fan design goes back a ways (witness the 485, introduced in 1972), and so was inherited by the 2465 as a tested design. There was plenty of other innovation in that scope for its time, and perhaps the "$20 computer type fan" wasn't all that common or inexpensive back in 1984 when the 2465 was introduced.
Your umbrage is misplaced. I'm only speaking from a historical perspective and reality. When the 2465A was introduced the cage fan was dropped in favor of a conventional design. If the Tek engineers felt it wouldn't do the job they would have continued with the cage fan.
I have a 2465 DMS with the cage fan that does the same shenanigans for about 20 minutes to about a half hour after initial power on. Then it calms down but is never whisper quiet and it makes itself known but isn't annoying.
Your umbrage is misplaced.
The 2465BCT has Option 09, which is the Counter/Trigger. See attached. This is from the 1986 Product Catalog and it's the 2465 Option 09 but the 2465B is essentially the same. I have this option on my 2465 DMS and it comes in quite handy.
I have a copy of the 2465B Options Operating Manual in PDF if you want it. Send me an e-mail at seanfinn999@gmail.com. I don't have a copy of the 2465B Options Service Manual but Artek Manuals does have it for sale.
But from what I now read this option 09 just -increases- the accuracy of the frequency and time measurement of the displayed waveform by using crystal-controlled reference. So my question here is, how does the plain 2465B take time/freq measurements without option 09? What kind of reference does it use? Or is the plain B not capable of taking frequency readings and display them on screen? I'm probably wrong but cannot understand why a sophisticated instrument like a 2465B does not have an internal high precision crystal-controlled reference to begin with. I understand the frequency counter on the B version is good up to 150-200MHz, so if its not going to be very accurate it does not make much sense to display the measurement numerically on screen.
As a comparison, in my 2247A everything time/frequency measurement based is related to the 10MHz internal oscillator, with an option to connect an external high precision 10MHz (Rubidium, etc) signal to substitute the internal one. By doing just two button presses I get dead on frequency (or time) measurements shown numerically on screen with 6 decimal places from a displayed waveform even it is only maybe half a division in amplitude, and up to 100MHz. Granted the internal 10MHz is not a OCXO and takes about 30 min to fully stabilize, but will be rock solid after that.
Does the 2465B also do frequency measuring like this?
But from what I now read this option 09 just -increases- the accuracy of the frequency and time measurement of the displayed waveform by using crystal-controlled reference. So my question here is, how does the plain 2465B take time/freq measurements without option 09? What kind of reference does it use? Or is the plain B not capable of taking frequency readings and display them on screen? I'm probably wrong but cannot understand why a sophisticated instrument like a 2465B does not have an internal high precision crystal-controlled reference to begin with. I understand the frequency counter on the B version is good up to 150-200MHz, so if its not going to be very accurate it does not make much sense to display the measurement numerically on screen.
As a comparison, in my 2247A everything time/frequency measurement based is related to the 10MHz internal oscillator, with an option to connect an external high precision 10MHz (Rubidium, etc) signal to substitute the internal one. By doing just two button presses I get dead on frequency (or time) measurements shown numerically on screen with 6 decimal places from a displayed waveform even it is only maybe half a division in amplitude, and up to 100MHz. Granted the internal 10MHz is not a OCXO and takes about 30 min to fully stabilize, but will be rock solid after that.
Does the 2465B also do frequency measuring like this?
You are actually asking something I have wondered about but nobody has been able to answer. I have a 2247A and more recently acquired a 2445B so I can only answer part of your question.
The 2247A has the normal A and B triggers but also a C trigger and universal timer/counter IC which is used to make voltage and timing measurements continuously in real time. The 2445B does the same thing using its A or B trigger (so the display blanks during measurement) and some form of microprocessor control which results in equally good voltage measurements but much lower resolution timing measurements and measurements are *not* made in real time with continuous updates; it makes a single measurement and then displays it along with the sweep.
I have no idea how the timer/counter variants of the 2465B series operate other than providing higher resolution and I have never seen a video showing them in operation.
Thanks for the input David. Lets hope one of the Tek gurus on this post can answer our question.
BTW, don't you love your 2247A? I know I do! (Disclaimer: no intention on hijacking this thread, not that it would even be possible) ;-)But from what I now read this option 09 just -increases- the accuracy of the frequency and time measurement of the displayed waveform by using crystal-controlled reference. So my question here is, how does the plain 2465B take time/freq measurements without option 09? What kind of reference does it use? Or is the plain B not capable of taking frequency readings and display them on screen? I'm probably wrong but cannot understand why a sophisticated instrument like a 2465B does not have an internal high precision crystal-controlled reference to begin with. I understand the frequency counter on the B version is good up to 150-200MHz, so if its not going to be very accurate it does not make much sense to display the measurement numerically on screen.
As a comparison, in my 2247A everything time/frequency measurement based is related to the 10MHz internal oscillator, with an option to connect an external high precision 10MHz (Rubidium, etc) signal to substitute the internal one. By doing just two button presses I get dead on frequency (or time) measurements shown numerically on screen with 6 decimal places from a displayed waveform even it is only maybe half a division in amplitude, and up to 100MHz. Granted the internal 10MHz is not a OCXO and takes about 30 min to fully stabilize, but will be rock solid after that.
Does the 2465B also do frequency measuring like this?
You are actually asking something I have wondered about but nobody has been able to answer. I have a 2247A and more recently acquired a 2445B so I can only answer part of your question.
The 2247A has the normal A and B triggers but also a C trigger and universal timer/counter IC which is used to make voltage and timing measurements continuously in real time. The 2445B does the same thing using its A or B trigger (so the display blanks during measurement) and some form of microprocessor control which results in equally good voltage measurements but much lower resolution timing measurements and measurements are *not* made in real time with continuous updates; it makes a single measurement and then displays it along with the sweep.
I have no idea how the timer/counter variants of the 2465B series operate other than providing higher resolution and I have never seen a video showing them in operation.
The 2465 does not have the capability to tie in an external reference like your 2247A. And I doubt the 2465A & B have that capability either.
The 2465 does not have the capability to tie in an external reference like your 2247A. And I doubt the 2465A & B have that capability either.
Option 1E on an oscilloscope with timer/counter option 06 or 09 adds an external reference input which accepts any of 1.000000, 3.579545, 4.433185, 5.000000, or 10.000000 MHz as a reference.
Option 1E on an oscilloscope with timer/counter option 06 or 09 adds an external reference input which accepts any of 1.000000, 3.579545, 4.433185, 5.000000, or 10.000000 MHz as a reference.
OK, that must apply to the 2465A or B. I have the complete option list for the 2465 and Option 1E is not listed.
I see answers so far have been focusing on the external reference input BNC option 1E. But that still leaves the real question unanswered as to why a sophisticated instrument like the 2465 (inc A&B) did not come with a high precision internal reference to begin with (not to mention a standard external input), but instead the buyer had to add options 06 and or 10 to get a higher degree of accuracy.
I wonder if it is possible Tektronix was mainly focusing on developing a higher bandwidth scope, and not so much on other (useful in my opinion) features that could have been easily added? Which features? again, take a look at the 2247A real-time on-screen measurements (frequency, time, volts, etc).
If this is the case, I for one am disappointed. I only rarely push my scope bandwidth needs beyond 100MHz, but I was instead looking forward that getting a 2465B would be (or almost) like a 2247A on steroids with 400MHz bandwidth and a somewhat nicer updated front panel functionality and design. Seems now to me that this is not quite the case, so unless someone can maybe disprove this, and with all due respect to the 2465, but I think I rather stay with my 2247A for now. No dying NVRam, no Hot deflection hybrid, and virtually no unobtanium parts.