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Tektronix 2465A SRAM Chip Replacement By Ferro Magnetic Ram A Great Success

By on June 11, 2021
Tektronix 2465A SRAM Chip Replacement By Ferro Magnetic Ram A Great Success

 

 

 

 

 

 

After some hesitation I today finally decided to start replacing the old 4464 SRAM in my Tektronix 2465A oscilloscope by a special Ferro Magnetic Ram chip type FM1608 from Ramtron. Below photo shows my scope as it was sold on eBay a couple of years ago by David from Texas in the USA.

Tektronix 2465A oscilloscope

And that was also before I later on also had replaced the old still from 1986 EaglePicher KEEPER 3V lithium backup battery like Robert from Texas in an article in the past showed on Jestine’s blog. And for the same reason I now also wanted to replace the old battery backupped D4464 SRAM containing 8192 bytes with all scope’s calibration data in it. Preventing losing the calibration of my rather expensive 350MHz oscilloscope in time after the battery no longer keeps that data stored in SRAM Memory. Which is most important when calibration done by professional firms – if they still do that for oscilloscopes over 30 years old – may well cost over 600 US dollar. Replacing the SRAM by Ferro Magnetic RAM thus has the big advantage that those chips do not lose their calibration data even when no chip voltage is present. And the retention time of these FM1608 is at least safe for another 10 years without any voltage in which they keep the present data fixed.

But before I really started removing that original 4464 SRAM chip I previously first had written down my scope’s registered Calibration data in SRAM addresses position 1E00 to 1FFF. Which the scope shows in its left upper screen after the front scope buttons DELTA V and DELTA T together with SLOPE are pressed to start the Diagnostics Menu. And with the COUPLING button and the up/down buttons we select EXEC 02 which is the RAM test to write down all 16 bits values plus even or odd parity. In total 00h to FFh 16-bit register values.

Also after that to make sure that I could save the entire 4464 SRAM as bin file to check my written down calibration values I used a modified 28 pin Testclamp to 28 pin socket test cable to read all data as 27c64 8K chip on my TL866II programmer. The test clip I used had pullups on pin 27 (/PGM) and pin 26 (nc on 27c64 but CE on 4464!) plus 1N4148 diode to pin 28 Vcc to prevent accidentally overwriting the present data in my SRAM. Reading the SRAM as Ram data on the TL866II is not possible because that is only a RAM test to check all cells in SRAM without saving any present data that would be lost without any external supply voltage anyhow.

And on my TL866II programmer I had PIN CHECK disabled because wires to pins 26 and 27 from Test clip to socket are unconnected. And IC type detection disabled too because the 4464 can’t be recognized this way and the TL866II doesn’t support this 4464 chip either.

Which gave me the entire correct 4464 data which was saved as bin file. And as said I noticed that all 256 (00h-FFh)16 bit calibration register values I had written down matched exactly those in the SRAM position 1E00 to 1FFF. I covered both eproms with a sheet of paper before taking below photo. Because they can accidentally get erased by the UV flash of my camera.

uv flash of ic

Previous photo showed my now successfully replaced old NEC D4464C-20 SRAM by the on a quality 28 pins socket placed programmed pin compatible RAMTRON 1608 Ferro Magnetic RAM chip. And I also measured if my new Keeper battery still gave the right voltage on pin 28 of my new FM1608 chip, which indeed was a perfect 3.3V.

For programming the FM1608 chip I however bought a new GQ-4×4 universal programmer because the TL866II doesn’t support these Ferro Magnetic Rams in a good way. And the GQ-4×4 does but still only the FM1608 and FM16W08 types. And the latter surface mounted version has even a much longer retention time than the DIP FM1608 chip version has. And I was able to buy 10 DIP versions on eBay for a fair price, but although the seller claimed they were new , they certainly were not!

However programming the 32K FM1808 and FM18W08 Ramtron types is required for replacing the standard 62256 battery backupped SRAMs or DS12xx Dallas types in the Tektronix 2440 memory scopes. Which is still possible but only on the GQ-4×4 by selecting the Dallas chip family DS1230y as useful replacement device. Something where the TL866II fails giving any support for Dallas chips or Ferro Magnetic Ram chips because it only resulted in many verify failures or it failed giving support at all!

Why the GQ-4×4 turns out to be a much better universal programmer. But still all programmers need many more updates before all chips are supported in the device list or any verify issues are completely solved. Like I experienced with the TL866II programmer.

TL866II programmer

On above photo the board was reinstalled in my Tektronix 2465A scope, the 5 flat cables reconnected and the 5 torx screws refitted. And the 2465A was completely ready to be closed and tested.

All scope tests PASSED without any issues whatsoever! Mission succeeded to my full satisfaction!

I now no longer need to worry losing my 2465A scope’s calibration for at least another 10 years or so. Next photo shows the cable with test clip I successfully used to read the content of the D4464 SRAM in my 2465A oscilloscope with. The 3M test clip became very expensive but mainly because of high shipping costs that made the clip almost 3 times more expensive afterwards! But it was needed!

2465A scope’s calibration

8192x8-bit ic

Above instruction for making the 2465A test clip SRAM copy cable => Use a safety diode 1N4148 to Vcc pin 28 to prevent accidentally shorting the backup Lithium voltage of your 2465A, and 2 pullups 100 ohm to keep /WE inactive and CE2 enabled on the D4464 SRAM on the test clip side!

I already know that reading the 62256 SRAMs in my Tektronix 2440 won’t be so easy as was possible in my 2465A oscilloscope this article was about. Because for some reason I was still unable to successfully read those with my for the 2440 specially prepared external cable with 3M test clip like perfectly worked on the 2465A Tektronix with the copied D4464 chip! Because I kept getting verify errors on my TL866II programmer. (Maybe I will repeat this read and copy test again with my new GQ-4×4 programmer? It likely may work much better as it did with the other chips where the TL866II kept failing at verifying!). But 2 brandnew FM1808-70 Dip chips are already waiting for the time they will also be replacing the old SRAMs in my Tektronix 2440 memory oscilloscope. And therefore I probably have no other choice than to just immediately replace the old SRAM or SRAMs in my 2440 first before any calibration is done. And afterwards when the Calibration is done the FM1808 chip or chips will automatically contain and keep the correct data in their memory. For also at least another 10 years!

And copying an already programmed FM1808 or other FM1608 chip is easy since no external voltage is required to prevent them from losing their internal data. And the chip can just easy be pulled from its socket to be read and afterwards simply be put back in its socket without any of the issues that battery backupped SRAM chips suffer from. Something that Tektronix hoped to solve by in newer models using the internally backupped Dallas DS 1230 and family chips. Those that I believe for some strange reason never were placed on sockets but soldered straight into the mainboard of the 2465B and other models. Probably because those modules were simply too high to easily fit under the metal outside of the case.

Recently I became a member on the special Facebook Tektronix family group. A daily growing family of Tektronix users and Tek tech lovers. Because even after 30 years or more these little machines are almost indestructible and very much wanted by engineers who gladly pay for a well supported brand of measuring instruments. On which even long after the warranty of service on these oscilloscopes and other equipment has passed, Tektronix still supports the world of Tektronix enthusiasts, by also sharing many much valued excellent service manuals for free. Although some people go to extreme and easily pay 50 US dollar for something as small as a knob to fix a broken knob on their very old but some still perfectly working Tektronix oscilloscope. Why others are already thinking of using a 3D printer to design and make hard to find replacements parts with.



Anyway this article was for those readers that also want to make sure they never ever have to recalibrate their expensive and much valued 350MHz Tektronix 2465A oscilloscope, that still but just also triggers up to signals with an incredible about 1GHz frequency! Don’t believe me? Just have a look at one of the contributions on the mentioned Tektronix Facebook group where someone showed just that!

albert from netherlands

Albert van Bemmelen, Weert, The Netherlands

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14 Comments

  1. Yogesh Panchal

    June 11, 2021 at 4:50 pm

    Albert,
    Thanks! for informative article.

    Likes(1)Dislikes(0)
    • Albert van Bemmelen

      June 11, 2021 at 9:34 pm

      After my 2465A oscilloscope's Ferro Magnetic upgrade in the meantime I also made 3 perfectly working Jim Williams Avalanche Fast Rise Pulse Generators. They are based on the OSH Park design boards that previously only worked with special 2N2369 HF fast recovery transistors. Only they could avalanche fast enough on about 90V DC. But since those transistors no longer can be found I modified the OSH Park circuit so that the OSH Park boards now also work with the few but still presently available 2N2369A transistors that only avalanche on voltages of at least 130V and higher! And these Jim Williams OSH Park boards can easily be used to check the bandwidth of any oscilloscope with. Maybe something to write about in a new article? But all that I now still need to do is also work on upgrading my 2440 Tektronix oscilloscope with these new Ferro Magnetic FM1808 RAMs. So that also the calibration of that scope in future is secured. And if that succeeds it definitely may be worth a new article.

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      • Albert van Bemmelen

        June 12, 2021 at 12:22 am

        PS: Normally you can not read an in-circuit connected eprom or sram correctly externally because when you activate the memorychip on its Vcc pin all other chips are also communicating over the same databus we try to read from! Like the buffers and the CPU that also start becoming activated which then causes a databus signal conflict. The databus is a parallel communication bus that sends signals In and Out (Bidirectional) and when two chips send signals at the same time over to another chip it won't work! Therefore the chips on the mainboard are also controlled in a way that only one is active and other chips go high impedance on their databus lines (Z state), so they will not interfere. Something I also have proven in a previous article when I needed a safety backup of the internal eprom from my dual channel 40MHz Kenwood oscilloscope with Read-out function. Which only was possible by remnoving the eprom to copy it, or by only providing the Vcc voltage to pin 28 of the eprom without also activating all other chips and mainboard circuits! Luckily the 2465A Tektronix is so designed that even when we provide power to the D4464 sram chip on pin 28, still none of the other ICs are activated! And there is no databus conflict because those other chips are really 'off-line' when the scope is powered off.

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  2. Paris Azis

    June 11, 2021 at 4:55 pm

    Excellent article, Albert.
    Most useful to all these lucky Tektronix owners who get now invaluable help in modifying their ancient memory circuits.
    I remember a relevant article of Robert Calk about him replacing the exhausted battery which supports this type of memory in his own oscilloscope...
    Long ago we had similar problems with the memory loss in TV tuners, where the relevant Ni-Cad battery pack, responsible to keep the 5V back up voltage when the set was off, was defective...The type of failure was “tuning possible, but station frequency storage impossible”...The memory content was immediately lost after switching off the TV set...

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    • Albert van Bemmelen

      June 11, 2021 at 6:49 pm

      I also know about those very ESD sensitive microcontrollers in those particular Philips TVs you mentioned. That mostly used 42 pin shrink dip controller chips on those mainboards. And the no doubt cheaper paperpressed thin brittle print circuit boards that were just made to save a buck or two on manufacturing costs.

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      • Albert van Bemmelen

        June 11, 2021 at 6:56 pm

        They also knew about the very sensitive microcontrollers that were used in those sets that collapsed after some static discharge. Which they after you bought a new replacement processor tried to prevent by including a metal shield you needed to solder over the processor. Like the cage of faraday to avoid any direct static discharge hit.

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  3. Parasuraman S

    June 11, 2021 at 6:57 pm

    Vow! What all things you can do! How about copying your brain RAM to this Parasu 'Ram'? So that this Ram also can do such wonderful things!(LOL)

    Likes(1)Dislikes(0)
  4. Albert van Bemmelen

    June 11, 2021 at 9:13 pm

    From what I've seen you already achieved many wonderful things Parasuraman! Sadly for European citizens buying from outside Europe (mainly from China) for electronic repair will be out of the question starting 1 July 2021. So my repairs and other electronic activities will be financially very limited thanks to Brussels (EU HQ Belgium). They now charge any parcel from outside the EU with 4 to 10 euro (depending on parcel value upto 150 Euro, or higher than 150 Euro) with 21% BTW (English VAT) plus additional import fees. Criminal charges that solve nothing since Europe doesn't make any parts since everything is made in China! Prices on Timber and other material already has increased to absurd high prices because of the Lockdown and bad EU laws!

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    • Parasuraman S

      June 12, 2021 at 1:34 pm

      The situations in almost all the countries are more or less same. You have come out openly, but many prefer to be silent for obvious reasons.

      Jokes apart, I hope one day will come, when we can download the software from one's brain and upload it to another, if possible the very needy portions! Looking at the way the technology, especially the biotechnology progressing, that day might not also be too far off! Anyhow, our lives might pass by that time!

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      • Albert van Bemmelen

        June 12, 2021 at 11:50 pm

        I do not think that biotechnology will be as promising as you'd like it to be dear Parasuraman. Because even a simpel and tiny virus can probably kill any biotec living 'device' instantly. But bacteriofagen are a great Russian bio invention that cure people from diseases where no existing antibiotic helps! (something they are really promising and experts in because they didn't have any antibiotics in Russia).

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  5. Anwar Y Shiekh

    June 11, 2021 at 9:24 pm

    I didn't even know about ferro-magnetic RAM; can it be corrupted by magnetic field?

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  6. Albert van Bemmelen

    June 12, 2021 at 12:35 am

    I suppose everything gets damaged or influenced in harsh environments like in space. But these are normal Earth conditions in which they do what they were designed for. Although I hope that they keep working because they were used in Ricoh devices (printers?) although the seller claimed they were new. All still had previous Ricoh firmware programmed in. And all 10 looked desoldered and a bit scratched on top. And I also got a worrying message that the DHL delivery was put asside because the parcel apparently was damaged in transport? But after a very long wait everything was received in good condition. And the long retention time is just as good as the times they can be reprogrammed!

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    • Anwar Y Shiekh

      June 15, 2021 at 1:51 am

      I meant by a strong magnetic field. If you have a spare with Ricoh firmware, it might not be to hard to bring a strong magnet near and see if the content is corrupted; just an idea.

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  7. Waleed Rishmawi

    June 12, 2021 at 2:10 pm

    wow. very deep sophisticated article full with information.. thanks for sharing and good job. have a blessed day

    Likes(1)Dislikes(0)

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