Tektronix TDS 380 NVRAM Replacement

I final­ly decide that I had pushed my luck far enough with my bat­tery backed NVRAM in my Tektronix TDS 380 oscil­lo­scope. The spec­i­fi­ca­tions for the Dallas Semiconductor DS1644-120 Timekeeping RAM state that it is good for at least 10 years at 25°C, and mine had just turned 28 years old.

Ferroelectric RAM ram replace­ment 32K X 8 SOIC to DIP

The DS1644 NVRAM stores all the cal­i­bra­tion data for the oscil­lo­scope, along with a Real Time Clock (RTC) for dis­play on the screen and time­stamp for saved files.
I did not want to replace it with one of the cheep Chinese knock­off IC’s that also have non-replace­able inter­nal bat­ter­ies, or one of the qual­i­ty func­tion­al replace­men­t’s with exter­nal bat­tery for over $73 USD deliv­ered.
Since I was not inter­est­ed in the time­keep­ing capa­bil­i­ties of the DS1644 or replace­ments, I decid­ed to try out a Ferroelectric RAM (FeRAM) that should be a drop in replace­ment except for lack­ing the time func­tion.
I ordered a Infineon Technologies FM18W08-SG which is a 130 ns 256K device orga­nized as 32 x 8 par­al­lel mem­o­ry, along with a SOIC28-DIP adapter board for a total of $18.80 USD.

Tektronix TDS 380 with new FeRAM pro­grammed and installed

There are quite a few screws to remove before the main acqui­si­tion board con­tain­ing the DS1644 IC can be removed, includ­ing four screws under the front bezel. The flop­py dri­ve inter­face board and many cables also need to be dis­con­nect­ed.
After care­ful­ly unsol­der­ing the DS1664 from the board, I placed it in my TL866II Plus pro­gram­mer and read out the mem­o­ry data and saved the file. I then placed the new FeRAM into the pro­gram­mer and pro­grammed it with the data. So far so good.
Important note: Be care­ful unsol­der­ing the DS1644 IC as there have been reports of data loss attrib­uted to over­heat­ing the IC. I unsol­dered 4 to 5 pins at a time, then wait­ed five min­utes before work­ing on the next group of pins until all pins were de-soldered.

TL866II Plus read­ing the data from the Dallas DS1644 IC

I added a 28 pin sock­et to the cir­cuit board so that in the future the next own­er could eas­i­ly replace my FeRAM mod­i­fi­ca­tion if required.
Did I men­tion that the real­ly nice thing about FeRAM is that it requires no bat­ter­ies.
After putting the TDS 380 back togeth­er it was time to pow­er the oscil­lo­scope up and see if the replace­ment works.

Tektronix TDS 380 oscil­lo­scope diag­nos­tics all pass
TDS 380 Signal Path Compensation suc­cess­ful­ly completed

Well every­thing worked fine, all the test’s passed, and the only indi­ca­tion that some­thing is dif­fer­ent is that the time and date on the dis­play remains set to 16 Jun 2024 12:31.

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