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Replacing Backup Battery On Tek 2246 Scope

From Tom Jobe, on Tekscopes:

Post #1

Recently there has been some discussion of 2246's and the back up batteries for them were mentioned, so I thought I would chime in with some 224X battery information for the archives just in case it would be of any use to anyone.

Most 2246 variations and the 2247A (and probably the 2245's) use a single 3 volt Lithium battery to power the RAM, but some 2246 1Y's use two silver oxide 1.5 volt batteries in series. The battery (or batteries) are on the “Measurement Processor” PCB board which is the board on the very top of the oscilloscope. In the limited number of 224X's I've worked on, I've found that the silver oxide batteries are coming apart and starting to make a mess of things but the single Lithium 3 volt batteries seem to be fine, even if they are low on voltage. This just might be my limited experience, so it will be good to hear what others have to say about this subject.

In looking around for some 3 volt lithium batteries with the 3 pin PC mount tabs welded on them, I found a good supply of them at the local monthly swap meet so I stocked up on them. They are normal 2/3 A Lithium batteries but with thin plates welded to the ends. Any number of other batteries would work well in this application, and there is a lot of physical room for other possibilities. The batteries I bought look exactly like the one pictured on this web page http://www.dantona.com/catalog/3.6V-LITHIUM-CYLINDRICAL-BATTERIES/MAXELL (it is the 8th one down the page).

Today I was working on a 2246 1Y that had the 2 silver oxide batteries that were spewing their contents on the PCB, and I noticed that the solder points were there for both the 2 coin cell batteries and the single Lithium battery. I removed the coin cell battery holders, scrubbed the PCB, and installed the single 3 volt battery (3.6 volts actually) on the bottom side of the PCB.

These coin cell batteries were mounted on the top of the PCB even though the manual suggests they were normally installed on the bottom, but there is plenty of room for the coin cell batteries (and their holders) on either side of the board.

The battery voltage does not seem to be very important as the RAM is normally powered from the 5 volt supply when the oscilloscope is actually running, but I have no idea what the minimum voltage requirement is for this battery's application.

tom jobe…

Post #2

Hello Everyone,

Mike Monett requested that I post the information I found on his “Tek 2465/2467/B NVRAM battery” problem. On eBay, “Qservice” is selling the Dallas non volatile SRAM IC DS1225Y, and they even offer optional programming of the SRAM with standard calibration data.


If this long link does not work for some reason, the eBay item number is

380042279862 so you can get directly to it.

In Qservice's auction for the IC, there is a link that will lead you to some Maxim information and the data sheet for the DS1225Y.




One of the above links also points you to Maxim's online buying site, if that might be a more convenient way for someone to buy a DS1225Y. http://www.maxim-ic.com/sales/

I looked in the 2465B service manual, and it looks like the part number for this IC (U2460) changed from 156-2473-00 (IC made by NEC) on the below 50k S/N scopes, to 156-2991-00 (IC made by Tektronix) on the above 50k S/N scopes. In looking at the component view of the A5 board in the manual, it appears that the RAM chip is the same physical size and pin count, on the above and below 50k S/N boards, even though many of the other chips appear to be surface mounted on the above S/N 50k, A5 circuit board. The A5 board is mounted vertically on the right side of the scope and the components appear to face outward, so it should be easy for one to compare the IC in one's scope to see if the RAM chip looks to be a 28 pin DIP, and physically the same as the one in the Qservice auction. Since there was no mention of any S/N ranges in the eBay auction from Qservice, I'm going to guess that the same 28 pin DIP SRAM chip is used in all of them. I believe that “Qservice” from Greece is quite knowledgeable about 24XX's, so it is difficult to believe they would miss something like the S/N range the RAM chip they are selling will work in.

Another thing that makes me suspect that all S/N's used the same IC, is that Maxim only offers the chip in a 28 pin DIP, but I suppose there could be other makers of this chip in other packages.

I remember there being some discussion of this RAM chip on the Tek forum, and I would encourage people to look through the archives for additional information about all of this. Also I remember some discussion about possible problems if you used faster memory, but this may, or may not, have been with this particular IC. Maxim offers this chip in both 150 and 200 ns, but the original chips in the 22XX's were 200ns according to the service manual. tom jobe….

PS Thank you Didier for the good information on the lithium cells!

tom jobe…

test_equipment/replacing_backup_battery_on_tek_2246_scope.txt · Last modified: 2013/01/08 19:00 (external edit)
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