Refurbishing Tektronix 24x5B scope - Page 1
Forum section: electronics / repair

author: Veketti
author_rank: Regular Contributor
timestamp: February 02, 2025, 07:39:20 pm
content: Hi,I lost my mindand purchased Tektronix 2445B oscilloscope. It should be in fully working order, but I was planning to refurbish it to make it a keeper. Change all the electrolytic caps and the notorious Rifas. Is there something else I should take into account? Did this model have some memory battery that will cause calibrations to lose if it empties? Is there a good remedy for that? Also when taking the boards out is there something to look after, like shouldn’t remove this or that or you’ll lose calibrations etc?Most likely the fan(s) are done, so any suggestions to change them as well and is there some specific model to use?Thank you

author: tggzzz
author_rank: Super Contributor
timestamp: February 02, 2025, 09:11:37 pm
content: There are good threads discussingallthemanydetails in this forum and TekScopes.A simple precaution w.r.t. losing the calibration data in the battery-backed RAM is to point a video camera at the screen and use the test sequence to step through the 256 locations. If you lose the cal data for any reason before it is transferred into new RAM, you will at least know the values that need to be re-inserted.

author: Kwakerman
author_rank: Regular Contributor
timestamp: February 05, 2025, 02:00:13 pm
content: Depending upon the serial number of your scope there are two different versions of the A5 board which stores the Cal data. The A5 is the long PCB on the right side (as you look at the front of the scope). Early versions are 'though hole' design and have a 'Keeper' battery (LTC-7P or something like that) on the right side of the A5, later versions are SMD and have the Dallas 1225 chip in the middle of the board. Early versions can have the battery replaced without losing cal data if you attach a substitute battery (or power supply) while you desolder and replace the battery. Later versions its a lot more difficult as you need to remove and read the data in the Dallas and then load it into a replacement. The 1225 isn't available new anymore but there are alternatives if you google it.If you have the later A5 and it has 4 SMD electrolytic caps then they need replacing and the PCB cleaning if they have leaked (they will). Also check for corroded tracks and out of tolerance components in the vicinity as that will throw the DAC voltages out and affect many settings and controlsIf running it with the cover off use a fan to keep the main PCB cool

author: chilternview
author_rank: Frequent Contributor
timestamp: February 05, 2025, 02:49:32 pm
content: Quote from: Kwakerman on February 05, 2025, 02:00:13 pmThe DS1225 is available from Mouser, I bought one for my 2465B a couple of weeks ago:https://www.mouser.co.uk/ProductDetail/700-DS1225AD-150

author: Kwakerman
author_rank: Regular Contributor
timestamp: February 06, 2025, 10:24:24 pm
content: Quote from: chilternview on February 05, 2025, 02:49:32 pmThanks, good to know.

author: Kwakerman
author_rank: Regular Contributor
timestamp: February 07, 2025, 08:55:40 am
content: Just out of curiosity did you note the battery manufacture date code so we can see how fresh these are?

author: chilternview
author_rank: Frequent Contributor
timestamp: February 07, 2025, 10:13:13 am
content: Quote from: Kwakerman on February 07, 2025, 08:55:40 amDate code is 2024 on the one I bought.

author: Kwakerman
author_rank: Regular Contributor
timestamp: February 07, 2025, 11:22:32 pm
content: Thanks

author: Veketti
author_rank: Regular Contributor
timestamp: February 08, 2025, 09:21:23 am
content: I seemed to be unsuccessfull in finding how to initiate the test sequence to see all the 256 locations. Could somebody tell how to do that?Other thing is, if the data from the RAM gets lost and have the data in video, how is it possible to restore it? I assume, getting bin file from someone and by hex editor inputting manually the records got from the screen? Is it according tothispost so locations: 0x1E00 and ending at 0x1FFF. Hope those are in same sequence that is shown on display? Is the bin file same for 2445B and 2465B?

author: tggzzz
author_rank: Super Contributor
timestamp: February 08, 2025, 11:05:32 am
content: Quote from: Veketti on February 08, 2025, 09:21:23 amIt is in the service manual, downloadable from the usual places, e.g. TekWikiQuoteYou would have to manually transcribe the numbers. Recording on video is an "if all else fails" backup procedure.I haven't seenwhereto enter them in memory (because I haven't had to do it), but that information will be available somewhere, e.g. here, tekwiki, TekScopes etc. I have 2465s, which don't have the problem.Howyou enter them will be dependent on you programmer. I don't think it is possible to do it in-scope.In the absence of other information, I would presume 24x5A/B have equivalent "bin files".

author: MarkL
author_rank: Unknown
timestamp: February 08, 2025, 08:50:11 pm
content: For dumping of the cal values, see the section in the manual on the EXER 02 diagnostic utility.The cal locations in the DS1225 are the same for the 2445B and 2465B. They are the same for all the 24x5A and 24x5B family. If you're doing a restore, all locations outside the cal data area should be initialized to 0xff in the DS1225. If you have your cal data, there is no need to use someone else's binary data (and in fact, you shouldn't).You will find varying opinions on this, but I would not encourage doing a wholesale replacement of caps unless you've found ones that are shown to be bad either through troubleshooting, direct testing, or visual inspection. The exceptions to this are the RIFA caps and a handful of SMDs which are known to have a high failure rate, as mentioned in an above post.Although it is long, there is a wealth of information in the thread you've already referenced:https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/Most of your questions have already been answered there.

author: Veketti
author_rank: Regular Contributor
timestamp: February 15, 2025, 08:18:33 am
content: Thanks. Got the calibration data from video. To get to the Exer 02 was by pressing and holding deltaV, deltaT buttons and hitting Slope -button. Then could scroll the Exer 02 by Trigger mode buttons and select by Trigger coupling up button.Opened the unit and found out that this doesn't seem to have the Dallas chip, so cannot change it to FRAM.. Is it so that only thing that can be done is solder backup battery for the time to replace new LTC-7P? Now I need to find new battery. Would EVEEF651625work?It looks this old battery is week 33 1988 so amazed that it still holds any charge...edit: Looks like the RIFA's been addressed already before. What do you think is there any reason to dig any deeper regarding those electrolytics?Thank you

author: Miti
author_rank: Super Contributor
timestamp: February 15, 2025, 12:33:17 pm
content: Congrats for your scope!I have a Tek 2445B as well, which I’ve got for free after a cleanup event at work. First, I replaced the capacitors in the power supply because the trace was wavy at power up and that fixed it. Second, I replaced the RIFA poppers for peace of mind. Then the FRAM. Then the capacitors on the motherboard … whiiich didn’t show any improvement. One thing that helped with the trace sharpness and brightness was a CRT adjustment that is described somewhere in the manual. It was very fuzzy with higher brightness before.Anyway, after I bought the Rigol, it became decoration. I use it with a Dutchtronic CRT clock just for fun.

author: calibrationfixture
author_rank: Regular Contributor
timestamp: February 15, 2025, 02:47:48 pm
content: Hi Veketti," Opened the unit and found out that this doesn't seem to have the Dallas chip, so cannot change it to FRAM.. Is it so that only thing that can be done is solder backup battery for the time to replace new LTC-7P? Now I need to find new battery. Would EVE EF651625 work? "Yes, this will work. Allready used 6 of these (same Source). The last in a 2455A.Calibrationfixture

author: Veketti
author_rank: Regular Contributor
timestamp: February 15, 2025, 05:16:55 pm
content: It seems that the U2460 (D4464C-15L) IC is the NVRAM. As I’ve already purchased FRAM FM16W08-SG I’m so tempted to install it. I cannot remove that U2460 unless I solder power supply to the pins and still I don’t know whether that would work to get it to reader and read the content. Found one blog, where someone read that chip in situ but seems too troublesome to make that kind of adapter. One idea that came into my mind is, now that I have the calibration data and I’ve found was it MarkL -template file for the newer Dallas chip with battery. Modify that file by hex editor and input the data that I extracted by EXER 02 to the locations 0x1E00 - 0x1FFF. Then burn that bin to FM16W08-SG and just replace U2460 with it. Would that work?

author: MarkL
author_rank: Unknown
timestamp: February 15, 2025, 10:30:52 pm
content: Thanks for reminding me that the NVRAM template was out there from years ago. Based on recent testing that was done on the NVRAM restoration utility, the unused locations in the template should be 0xff (and not 0x00). I have corrected the file in the original post, so you should pick up the updated one.The old one will still work, but it can cause lock-ups on boot and nonsensical settings. 0xff seems to work consistently.Please grab the updated one and post back if you encounter any issues with it:https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1935220/#msg1935220The procedure you outline for putting the data back is correct.As far as the FRAM itself goes, be aware it is not a drop-in replacement for the old SRAM. The FRAM has different power-up and power-down requirements which is not implemented by the old SRAM circuit. That being said, by a stroke of luck it works for nearly everyone who has tried the FRAM replacement. There was one person (Miti) who had corruption issues and found a workaround here:https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg2005880/#msg2005880

author: Veketti
author_rank: Regular Contributor
timestamp: February 16, 2025, 09:09:30 am
content: Wonderful, super helpful! Thanks.One thing that makes me wonder. I found from github usergkeethhad uploaded his 2465B NVRAM backup and checking the content there is lots of data before the 0x1EE. Any idea what is that data and is it in anyway essential for the scope? Or is it just some usage statistics data like, how long the scope has been on etc.?

author: MarkL
author_rank: Unknown
timestamp: February 16, 2025, 04:13:53 pm
content: Quote from: Veketti on February 16, 2025, 09:09:30 amThe SRAM chip is also the processor's run-time memory. The range outside of the calibration area of 0x1e00-0x1fff is used for operating data, such as the stack, variables, parameter passing, etc. Much of that memory gets initialized when the scope boots so it's in a known state for the firmware.Some areas outside the calibration data are used as NVRAM for storing setups and the last known position of front panel encoders, buttons, etc. This is why random data, or even 0x00, left in these areas cause boot and settings problems.So, when you encounter a complete SRAM image from someone else, you're going to see all this leftover data outside the calibration area.There is not a known memory map for the data in SRAM, including the calibration data. The first two bytes at 0x1e00 is the calibration data checksum, and a couple of other entries are known here and there, but the entire block is considered opaque. Forum member Siggi has figured out more of of the 24x5 memory mapping by using Ghidra to disassemble the firmware. You can search for his posts on the TekScopes list on groups.io if you want to learn more about it.I don't recall where the hours counter resides. I *think* it's in with the calibration data, but I'm not certain. If it's in the calibration data it will be restored when you reload the FRAM. If you care about the hours and power cycle count, take note of them before removing your old SRAM. There is an on-screen utility (CAL 05) to set these values manually if I'm wrong.EDIT: Fix ambiguous statement on checksum.

author: Veketti
author_rank: Regular Contributor
timestamp: February 18, 2025, 08:15:53 pm
content: I’ve seen much debate whether the U800 need extra cooling as it’s running very hot. This must be one of the most controversial topic, but in my opinion excessive heat is never a good thing but due to not finding any ready made heat sinks decided to machine one from aluminum. This will greatly expand the surface area of that IC and help it running cooler.

author: MarkL
author_rank: Unknown
timestamp: February 18, 2025, 08:59:19 pm
content: https://groups.io/g/TekScopes/message/152372

author: Veketti
author_rank: Regular Contributor
timestamp: February 21, 2025, 07:35:51 am
content: Thanks MarkL for that link. However I added thermal paste to maximize the heat transfer and snug the nuts by only finger tight with the socket so it's impossible that I overtightened. Also impossible for the heatsink to drop and cause issues.I made two of these so if someone is interested to get the other one PM me.

author: Kwakerman
author_rank: Regular Contributor
timestamp: February 23, 2025, 04:57:47 pm
content: I have noticed that some PSUs have had the two input RIFAs replaced on the regulator board with the red ones from new so that is good, however there are potentially another 3 RIFAs on the A3 inverter board as I've had PSUs with the red caps on the regulator board but cracked RIFAs on the inverter board. Have a look for A3C1020, A3C1051 and A3C1052 in the manual. If you look carefully at the position of A3C1020 you can just see the bottom part of it in the gap between the pcb and aluminium heat sink (once the top cover is removed). If you see that RIFA coloured epoxy then they need to be replaced too.

author: Kwakerman
author_rank: Regular Contributor
timestamp: February 23, 2025, 05:03:22 pm
content: I've got a 2465A in for repair at the moment, it has over 27500 hours on it on the original U800 (without heatsink) so I think the chip is generally a good design but they are probably susceptible when people block the air vents or don't fixing failing fans. I keep mine as Tek intended and haven't had an issue with my 5 scopes but then again I also make sure they have the correct airflow.

author: Homer J Simpson
author_rank: Super Contributor
timestamp: February 24, 2025, 01:04:55 am
content: In this video, starting at about 19:00 it goes into adding a temporary battery while replacing the original battery.The original battery is available from Mouser for sure.I have done two of these without issue.I did use the bench supply rather than the battery pack.From the channel "NFM"https://www.youtube.com/@NearFarMedia/videos

author: Veketti
author_rank: Regular Contributor
timestamp: March 27, 2025, 07:24:40 pm
content: So I finished my refurbish. Ordered capacitor kit from Condor Audio which included all the caps. There were some oddities like the red rifa caps on power board and on A5 board one of the capacitors were 63V when manual states it to be 25V. It was sprague -brand and I'm pretty sure it was original from factory. Maybe they've run out of 25v caps? PSU had both of the parallel 15 ohm power resistors blown open for some reason. Other rifas on PSU were the bad clear plastic encased ones and only two were the red better ones.Changed also the memory battery and used lab power backup with exactly the same voltage applied than the old battery was. I had FRAM chip ready programmed but didn't change that.

author: Kwakerman
author_rank: Regular Contributor
timestamp: March 27, 2025, 10:42:35 pm
content: Worth using a sharpie pen or similar and write the battery replacement date inside the scope (on top panel perhaps). Give it a few years and you will have trouble remembering the date, also good info for next owner if you sell.Then again I suppose you could always refer back to this thread.