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Tektronix 2440 Oscilloscope Repaired- Part 3

By on September 30, 2015
Tektronix 2440 Oscilloscope Repaired







Here is the part 2 article:

Today I started with Calibrating the 500MS/s Tektronix 2440 Memory Oscilloscope. Something that was easier then I first anticipated. Mainly because it is a pleasure to work with this (and probably any other Tektronix Oscilloscope) really fine assembled Device. And the beautifull way in which every piece of hardware is documented, and can be found when any repair is neccessary.

I began reading in the Tek Service Manual thinking it would take a lot of work and time to Calibrate or even to understand the Diagnostic Messages of this 2440 Scope. But it wasn’t. But there are also several ways to do the Calibrating thing.

First there is the Automatic SELF CALIBRATION which is the easy way. And that requires no external test equipment. The Built-in computer firmware in this case is used for calculating the over 100 Voltages, that control Gain, Offset, and so on. Second there is the external calibration method. Jumper J156 has internally to be removed. And external equipment is needed to Calibrate all electronic circuits.

Of course I tried the easy method, and running SELF CAL showed up on screen. But to start this I had to press the Button MENU OFF/EXTENDED FUNCTIONS (once or twices depending what is presently displayed on screen). And after this Extended Functions Menu is displayed, I pressed the menu button CAL/DIAG.

Tektronix 2440 Oscilloscope Repair

On previous photo the first visible Screen was seen that presented itself after the Bad PMI DAC10/U250 horizontal deflection chip was replaced by a new chip. And the internal Built-in Diagnostic Start-up Test had finished after Powering Up.

It sadly showed not less then 6 FAIL messages. And every message can be viewed into deeper for more info. But the FAILS preventing me from using any of the normal Oscilloscope functions.

After with some playing around with the Screen Buttons I understood that SYS_RAM U664 (a Non volatile 32k x 8 RAM) probably was partly defect. Cost on Ebay about $30 dollar. Okay since it was not my Scope my friend has to decide it was worth the Gamble.

I also menaged to reduce the Fail count to 5 after a few Startups which was good.


I found out that SYS-RAM component U664 in the schematics was only partly bad (a DS1230 that is called a 2374 chip on the System Processor Board [A12 Board]). As can be seen on next photo. And on the following photo you can see deeper into which part of the U664 SRAM Failed in the test.

But I still wasn’t able to get into the Normal Scope Control Mode probably because of the too many FAIL messages.


After reading the Service Manual on how to startup the ‘Automated Self Cal’ it finally started running. And this display was shown every time I started up the Scope again.


And it got automatically the FAIL count down to only 4 FAILs left. See next Photo.

But probably FAIL line 3000 means that the Nonvolatile SRAM chip (28 pins) has to be replaced before the 3 following FAIL Messages will be dissolved. Or at least it is the best action without having to Re-Calibrate the Scope’s CCD-Modules etc. manually afterwards. And the 2440 oscilloscope probably sometimes Freezed in executing all its functions because of this bad SRAM. But that is not proven yet.

But as I found out further on in this article, the SELF CAL function really works in Helping to restore the Scope’s old functions.


And as can be seen on previous photo the AUTOSETUP is working which Helps to gain control over the front buttons on operating the Scope.

Not soon after the Scope Self Calibration began to showing its great work, the old Wave Signal became visible on the CRT screen. See photo below.


Next Photos show that the 2440 Memory Oscilloscope really is working after the Built-in Self Calibration function.





And last but not Least here is a photo of the 50 Hz Sinus picked up by the Probe. 2mV/div.

Tektronix 2440 Oscilloscope Repair

So probably all scopes on Ebay with 6 Fails or less can be repaired or Fixed. Especially since this repaired 2440 Oscilloscope was completely dead on arrival (DOA). And now is totally back to life!










Albert van Bemmelen, Weert, The Netherlands.

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  1. Paris Azis

    September 30, 2015 at 5:47 pm

    Hello Albert

    Very good job ideed!
    Thank you for sharing this experience.

    Best Regards

  2. Albert van Bemmelen

    September 30, 2015 at 7:56 pm

    Thanks Mr.Paris.
    The mentioned DS1230 SRam U664 are in fact later replaced by HM62256 SRams at Tektronix Manufacturing (without having the Lithium Memory conserving Backup as the DS1230 did have).
    That complicates copying the original Calibration Data inside. When I do need to replace the Bad HM62256 Ram by a new one I better copy the content first with a normal Eprom programmer. But because the U664 was mentioned in the Service Manual as being a DS1230 which it aint that is almost impossible. And External Calibration probably will be necessary afterwards.

  3. Robert Calk

    September 30, 2015 at 10:16 pm

    Good job, Albert. Thanks for sharing the repair with us.

    • Albert van Bemmelen

      October 1, 2015 at 12:17 am

      Glad you liked it Robert. Thanks to You I've become a complete Tektronix Fan. And since you made me aware of the affordable 2465A Tektronix 350 MHz oscilloscope, you are in a way my Tektronix Master.
      This Tektronix 2440 Memory Oscilloscope with 300 MHz and 500MS/s is no different and also perfectly designed and also a very friendly machine. (But sadly not mine). As you saw it even does work, and only has 4 FAILs left that needs some further attention. But even if it still didn't work and had 6 FAILs or more left, it would cost $347 dollar or more on Ebay.
      (NEW listprice 1988 $11.600 dollar !).

      • Robert Calk

        October 1, 2015 at 7:50 pm

        Hi Albert,
        Thanks for the kind words but I'm no Tektronix master. Our scopes were very expensive when they were brand new. They do look like a beautiful piece of artwork on the inside, don't they?

        • Albert van Bemmelen

          October 2, 2015 at 4:49 am

          They sure do Robert! And the nice thing of these Scopes is also that lots of old and dirtcheap TTL/CMOS IC's are used inside. Only the special Hybride and components like the DAC's make repairing a little more difficult and more costly to replace if they are ever. They at Tektronix really thought through the overall design and the way in keeping them easily in perfect working condition when servicing is necessary. And the best part is that even 30 years later they work at high frequencies that still can compete with todays Oscilloscopes. And even the way to control the knobs and buttons is thought through very well too! (I sound like a Tektronix Salesman by now I guess).

          • Albert van Bemmelen

            October 2, 2015 at 4:58 am

            PS: As you probably can see, I had to Dim the Intensity of the Scopescreen. Because the CRT Tube still was so very bright after all those (36600 hours operating time ?) years that it was more difficult not to make an overintensified photo.

          • Robert Calk

            October 3, 2015 at 12:43 am

            I was amazed at how clean and beautiful my scope was - I thought it was an artistic masterpiece. Mine has less than 2000 hours on it.

            • Albert van Bemmelen

              October 4, 2015 at 2:02 am

              I was not so lucky as you and my friend Erik were since my scope already had about 48873 working Hours on its internal counter. I don't know what the maximum life expectancy value in Hours will be but I hope it will last at least another 48900 hours more before it quits on me. But recently my friend Erik was also sold the wrong LTC-7PN (yellow 6 gram lithium) batteries without the 1.6Kohm resistor and protection diode. The USA firm on Ebay did that also when I ordered a LTC-7P from them. It looks like they do it on purpose. To sell batteries twice?

              • Robert Calk

                October 5, 2015 at 12:40 am

                I'm not sure about that - I bought my battery from

                • Albert van Bemmelen

                  October 5, 2015 at 3:45 pm

                  I know Robert but the problem for us Guys in Holland is that no one, including Mouser, is willing to sell us these simpel Lithium Batteries coming from the States. Only the Ebay guys are willing to do this at acceptable prices. But as I've said before, they first keep selling us the not ordered LTC-7PN batteries ($40 excl. Shipping). And when I told them that only the LTC-7P which was ordered, and previously also was shown on Ebay, had an extra internal protection circuit with an extra 1.6Kohm Resistor and Diode (preventing burning out any copper layers in case of any short circuiting), they also did send me the originally ordered battery.
                  PS: I just completely managed to Calibrate the 2440 Memory Oscilloscope which saves me the $600 dollar that they do ask for Calibrating these Tektronix Oscilloscopes. Final repair part#4 will show that anyone can do this easily himself!

                  • Robert Calk

                    October 5, 2015 at 11:40 pm

                    I don't have good enough equipment to calibrate a scope properly. I'm glad the repair worked out well for you.

                    • Albert van Bemmelen

                      October 6, 2015 at 9:35 pm

                      I think however you do Robert. Because you would only need to connect several Voltages up to 20 Volt that you exactly measured and adjusted with a standard Universal Multimeter. And you just Calibrate your Tektronix with these Voltages by using the EXT Diag and EXT CAL functions thats Built-In every Tektronix Oscilloscope. And maybe a few Calibration tests more.
                      But the best part is that you don't need to if the also Built-in SELF Cal and SELF Diag functions manage to do that for you automatically!
                      If you see Final part #4 of the 2440 Oscilloscope Repair you will understand. You only have to follow the very clear instructions in the Service Manual to be sure how to do that if you would use the EXT Calibrating modes.

                    • Robert Calk

                      October 8, 2015 at 2:28 am

                      According to my service manual, you are supposed to use much better equipment than a standard DMM. Also you need a good waveform generator and other expensive equipment to calibrate a scope correctly.

  4. aziz

    October 1, 2015 at 3:13 am

    Thank you

    • Albert van Bemmelen

      October 1, 2015 at 7:09 pm

      Thank you Mr. Aziz for your appreciation.

  5. Zed Pato

    October 2, 2015 at 10:16 am

    nice sharing this information sir Albert

    • Albert van Bemmelen

      October 2, 2015 at 11:43 pm

      Glad that you liked it Mr. Zed Pato ! (No need to call me sir ! I'm not knighted yet LOL)

  6. Yogesh Panchal

    October 2, 2015 at 3:29 pm

    Thanks Guys lots of knowledge update is also available in your conversation in comments also.

    • Albert van Bemmelen

      October 2, 2015 at 11:39 pm

      Yes indeed Mr. Yogesh. I must confess that it happens to me that I find new information that I also could have integrated into the article. But it came after the article was already send in. So I use the opportunity the add any interesting new info to any of the Posts that follow my article. This way hoping to upgrade the article to keep it complete.

      • Albert van Bemmelen

        October 4, 2015 at 2:16 am

        I have just printed out the at least 530 pages of the complete 2440 Service manual. And I've read on page 6-77 about the troubleshooting Procedure for the Scopes Diagnostic 3000 Fails at addresses 3710 and 3810.
        You can simply run both tests in CONTINUOUS mode and by measuring with the Channel 1 Probe on PIN 20 of U664 check if it is LO. If it is a HI then you need to check on component Q960 and that circuit.
        Then check with Channel 1 Probe for a HI on pin 26 of U664 (Chip Select). If you measure no HI you must look at component U424A for problems.
        This really explains how easy repairing a Tektronix Scope is by using the Diagnostic Test program that is Built-In.

        • Albert van Bemmelen

          October 4, 2015 at 2:31 am

          By-the-way: I forgot to mention the very interesting part that the Built-In Diagnostics Test is able to completely test the U664 Calibration SRAM by first copying its content to the second SRAM on Board that normally is occupied by the Wave Signal Building presentation.
          After the 3000 test has tested the entire U664 SRAM Memory, the original Calibration data is copied back from the second WAVE memory SRAM.
          It is a really perfect Tektronix creation!

  7. Mark

    October 6, 2015 at 5:42 am

    Hey Albert, well done on a well written and informative series of articles! It is pretty rare that there is only one fault with a component and you have done well to trace all the faults. Isn't it great when you come across a well engineered piece of equipment that was built to last. I have recently acquired an old Russian analogue galvanometer that is beautifully crafted, including a draw at the bottom for all the current shunts. I have been looking on the net to try and find the maker and age, but can't find it anywhere. It is a thing of beauty! Just like some of the older electronic units, like your Tektronix, things were built last. Now a days, a lot of appliances seem designed to create land fill.
    Thanks again. Keep up with your repairs and articles!

    • Albert van Bemmelen

      October 6, 2015 at 10:21 pm

      Hi Mark, the Oscilloscope was defect at the Diode Bridge, the mentioned PMI DAC10, and of course the Primary Fuse. So there were 3 defective components that I had to replace.
      What component was the first to go out of order, or went defect, I'm not sure. But after the Diode Bridge was replaced the Fuse short circuit already was gone and all (+ and -) 5, 8, 15 voltages , and the 10V REF measured exactly their values without any load attached (J102 and J166 open). Except the 3 voltages that without load were higher as mentioned in the article.
      You are very right that these devices are still worth kept working, no matter how many years they have had. They were at the time they were built top of the Bill and even today can compete with todays equipment! Especially because off the high RF/HF frequenties they can handle.
      About your Russian Galvanometer, I have one also but when I after many years opened the Aluminium Box to have a look at it again, I noticed that the special cushioning inside had damaged the front of the meter because of the chemical substance in it. (somekind of sulfuric acid). So beware of the material in which your device is packed. My meter was okay but the text on the Aluminium Front was a little damaged.

  8. amendar

    October 6, 2015 at 12:43 pm

    Hi Albert,
    Thank you for your share. Very interesting and useful for me.
    Would you possibly help me to know if there is a way like self cal / self test to find out the working hours of a tektronix 465 or 475 series?
    Thank you very much.

    • Albert van Bemmelen

      October 6, 2015 at 9:45 pm

      I'm sorry dear Amendar, I only know about the 2440 and the 2465A Tektronix Oscilloscopes. I think you can find it in the Service Manual of your Tektronix Scope, like I did find it in mine. I do not know if your 465 or 475 Document is obtainable for free on the internet. But if they at Tektronix did a as good a job with your Oscilloscope like they did with mine it must be explained in there!

      • Albert van Bemmelen

        October 6, 2015 at 11:36 pm

        Amendar , I must disappoint you. I just downloaded the Servicemanual for your Oscilloscope on (July 1975 version, 291 pages).
        It seems that your oscilloscope doesn't use any microprocessor or pc controller board like the later Tektronix Scopes do. And therefore that option isn't available for your scope. Just as the Self Cal or Self Diag probably will not be possible on your 465 Tektronix either. And even the Schematics and Diagrams in the 465 Service manual seem to be completely drawn by hand, instead of made with the help of modern Personal Computers and/or Designing Software. Sorry !

  9. amendar

    October 7, 2015 at 12:29 pm

    Dear Albert,
    Thank you spending time and study sm of 465, you did a great job man.
    I hope it will be enough if the scope that, I'm going to buy, passes normal tests and calibration.
    Since its not used for 12 last yrs as owner says, I hope its not as much old and tired! That can make me not to buy it.
    Again thank you .

  10. Humberto

    October 7, 2015 at 11:13 pm

    Well Albert, mission accomplished at the end. Congratulations and keep up.

    • Albert van Bemmelen

      October 9, 2015 at 4:41 am

      Hi my old Cuban friend. (And it is no Havana. LOL). I've noticed your photo on LinkedIn so I sent you a LinkedIn message. I'm not a real fan of LinkedIn or for that matter FaceBook but I always want to keep in touch with friends.

  11. Albert van Bemmelen

    October 8, 2015 at 3:46 am

    No Problem Dear Amendar, I understand. I hope the Tektronix 465 will be working fine and will be worth your paying price. There is of course still a calibration part in the Service Manual for the 465 Oscilloscope you can follow if you need it. But it will be different compared to a younger Tektronix 2465A or a 2440 oscilloscope. Glad I was able to answer your question.


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