Re: TEKTRONIX TDS380 FAIL++ CAL INITALIZATION  - Page 1
Forum section: electronics / repair

author: lintonbrown
author_rank: Newbie
timestamp: September 09, 2025, 04:05:48 pm
content: I just brought a Tektronix TDS380 from ebay. I do not know much about the TDS SERIES. Turning on oscilloscope shows fail++ cal intialization. Just need more information on what to check next. I hope someone can help me. I have 3 pictures to post

author: TinLethax
author_rank: Regular Contributor
timestamp: September 10, 2025, 12:04:11 am
content: From the error it seems to be related to the Dallas NVRAM dying. I've heard that these TDS XXX series have a ticking time bomb problem with this Dallas NVRAM chip thing (The small black rectangle DIP that embedded with battery inside the epoxy package). I think there were several forum members that went into the replacement procedure, some replace it with FRAM and no longer need that backup battery.

author: lintonbrown
author_rank: Newbie
timestamp: September 10, 2025, 01:26:43 am
content: What do I need to do next in replacing the Dallas NVRAM. What is the best way to fix this NRAM problem with new Dallas NVRAM or something else. Do I have to program the new DallasNVRAM chip. I am just lost about all this. Thanks for all your help.

author: lintonbrown
author_rank: Newbie
timestamp: September 10, 2025, 03:13:11 am
content: Where do I fine the information that several form members used that went into the replacement of the Dallas DS1644-120 with FRAM chip without battery. Thank again for your help.

author: TinLethax
author_rank: Regular Contributor
timestamp: September 10, 2025, 09:00:18 am
content: I found this one for the TDS3XXhttps://www.eevblog.com/forum/repair/dallas-ds1644-timenvram-battery-mod-on-tds340360/msg3605943/#msg3605943It requires you to essentially pry open the chip epoxy, remove the old cell and solder wires to the external battery.You can also check this one too. It was for the TDS500x TDS6xxhttps://www.eevblog.com/forum/testgear/tektronix-tds500600700-nvram-floppy-dump-tool/msg4896836/#msg4896836Not so sure how similar these two and the TDS3xx are.Another one is similar. Replacing with FRAM but it's for the HP scope. Not so sure if it works with Tek but you can try

author: ArcticGeek
author_rank: Regular Contributor
timestamp: September 10, 2025, 08:45:58 pm
content: Before worrying about the NVRAM, I think the next step is just to verify if the scope will work or not. It's been sometime since I've had a TDS380, so I can't so for sure but most likely the scope will still work with a bad NVRAM.After you get the error message for the cal initialization, go ahead and press clear menu and see if you can see the traces for CH1 and CH2. If you can, attach a probe to each channel and see if it will trigger on the probe compensation signal and display the signal on each channel.If that works go ahead and try to run SPC in the utility menu. If that completes successfully then you know that your scope is in pretty good working order aside from the NVRAM error; and at that point you can focus on that issue.Early models of the TDS500 and TDS600 relied on the NVRAM to store calibration settings as well as SPC settings, but I don't THINK the TDS380 did - I think those are stored in a serial eeprom.Once we know how well the scope is working (or not working) we can possibly advise what the next steps are.Best,

author: lintonbrown
author_rank: Newbie
timestamp: September 10, 2025, 10:11:51 pm
content: I have checked both channels and all is ok with volts and frequency. I run the SPC and it passed but I did not let it warm up for 20 minutes. Just one thing and what about the External Tigger Uncaled or just wait till later for that.Again thank you for you help.

author: ArcticGeek
author_rank: Regular Contributor
timestamp: September 11, 2025, 12:09:45 am
content: This is very good news that it passes SPC and the voltage and freq is correct on both channels. Don't sorry about the 20min warm-up, that is just to make sure any DC offsets at low (<10mv/div) voltage settings. SPC is a good way to test the acquisition system to make sure it's working properly, and if that passes its a great diagnostics. I wouldn't worry about the aux input; the calibration is for CH1 and CH2 and the variation in the attenuators at different v/div settings. The aux input doesn't have any variable attenuation so there shouldn't be anything to worry about.At this point its time to start looking at the NVRAM. You'll need to open up the scope and find the NVRAM - it's a Dallas/Maxim part that is encapsulated in all black. If I recall correctly the TDS380 used a DS1644 but I may be wrong. Let's find out what part it is before we go looking for a replacement or alternatives. I think the acquisition board on that scope is on an add-in card so you'll want to check. Download the Service Manual from tek.com - that might be helpful.There are also full schematics for the TDS380 floating around on the web somewhere - I know I've seen them. You likely won't need them though for this repair job.Report back on what the NVRAM part number is and we can go from there.Best,

author: lintonbrown
author_rank: Newbie
timestamp: September 11, 2025, 12:51:11 am
content: DALLASDS1644-120TIMEKEEPING RAM9634B2U

author: ArcticGeek
author_rank: Regular Contributor
timestamp: September 11, 2025, 12:56:27 am
content: I found the TDS380 Technical Reference schematics on the TekWiki website here:https://w140.com/tekwiki/wiki/TDS380From the schematics I can see that the NVRAM in that scope is a DS1644. Depending on how ambitious you are, you have several options:1. You can buy a DS1644 replacement on ebay from a user "kellyjo". I have no affiliation with that seller, but I can attest to the quality of goods as I've purchased a few of the related NVRAMS for the TDS6XX and TDS7XX scopes. The price is reasonable, although not super cheap. It is however, a plug-n-play solution and offers the capability of being able to replace the battery.2. You can purchase a DS1744-70 from Mouser or Digikey. From a quick glance at the datasheets they appear to be pin and register compatible, but double check to make sure the register assignment and bit definition is the same. This is also a plug-n-play solution but you lose the ability to replace the battery. Although the battery is spec'd for 10yrs of life, I'd say its reasonable to expect a 20 year life from them, and by that time you may no longer own the scope.3. You can buy a DS1744P and the mating PowerCap board and design your own. You would have to make a board that would bring the 28pin DIP pinout to mate with the 34 pin PowerCap.4. You can design your own with an FRAM - but be careful as the FRAMs are 3.3V IO only and these scopes have a 5V data and address bus.5. Search here on eevblog for DS1644/DS1744 FRAM replacements and solder your own after getting a board made using their Gerber files.My recommendation is probably either #2 or #1, but its up to you. Avoid buying anything from China on Ebay that claims to be "new" - there are TONS of posts here on eevblog and elsewhere about how these are fakes. A clear giveaway is when you see a date code on them from 2023 or 2024, etc....these parts were obsoleted by Maxim way back in the ~2009 timeframe!Another important thing to do is install a machine-pin DIP socket in the spot where the NVRAM was. This gives you options later on if you need to replace again.Best,

author: lintonbrown
author_rank: Newbie
timestamp: September 11, 2025, 03:04:17 am
content: If I buy a new DS1644-120 and new socket and what do I need to next. Do I have to program it or recalibrate the TDS380 or do something else. I will look at the other eevblog sites to see more about all these DS1644-120 problems which some other person wrote "a ticking time bomb" in the TDS SERIES.Many thanks for your help.

author: ArcticGeek
author_rank: Regular Contributor
timestamp: September 11, 2025, 01:19:41 pm
content: The steps that need to be completed are essentially this:1. Desolder the existing DS1644 from the board. This is best accomplished by using a high quality desoldering tool such as the Hakko 808 or similar. I have done this job using solder wick and a good iron, but it can be a real pain in the a$$. The VCC and GND pins are especially difficult since those pins are connected to power planes on the board and require a lot of heat.2. Read the contents of the old DS1644 with an EPROM programmer and program that data into the new part. This step may not be necessary since the contents of your old part are garbage. If you can find a dump of another TDS380 NVRAM (there are other users that might have one), that would be a good option.3. Solder the new socket and install the new part in the scope and power on the scope. If you haven't obtained a good NVRAM image you will still get the cal init failure at this point.4. If the calibration data is not stored in the DS1644, then you can likely get rid of the Cal initialization failure by simply re-running SPC, setting the date and time, and power cycling the scope. I think this might be the case but I don't know for sure. If this works, step 2 isn't necessary. However, if you still get the Cal init failure then the DS1644 needs to be loaded with a valid image to get rid of the failure or else you will need to do a full calibration of the scope. Like I say, if you look around various sites and/or ask for a TDS380 image you can probably get one.Good luck!

author: lintonbrown
author_rank: Newbie
timestamp: September 11, 2025, 01:59:34 pm
content: Thank you for all your help and I will let you know when I get the parts put in the scope and power back up to see how the new parts work out. It might be few weeks before I get all this together.Linton Brown