Tek 2440 Repair - Battery/RAM.

Brian Gaff

Hi All - I've reviewed the posts here regarding the repair of a Tek 2440 due
to dead batteries in the Dallas Semi NVSRAMs. Notwithstanding the great
information in those posts, as well as in Hugo Holden's August 2013 paper,
I'm looking for someone with experience doing that repair who can handle
that for my 2440, and calibrate it. Please reply if you can suggest
someone. Thanks.


I’ve done that repair several times. The Dallas chips were available from Digi-Key but I hear some had replaced them with modern SRAM. I opted to use the original DS1220’s from digikey in my scopes. I also recapped the supply’s while I was in there. It’s not a difficult task. The only issues I ran into was the main processor was dead in more than one unit so I had to find a supplier for that which was not easy. At one point I had a ZIF socket installed in a 2440 auditioning CPU’s. That was fun…

It’s early and I’m on my phone. Later I’d be happy to dig out my notes and find some links for you if you’d like.


Heres the memory replacement I used: https://www.digikey.com/en/products/filter/memory/774?s=N4IgTCBcDaICIGUCMYwAYCCAhEBdAvkA
Specifically DS1220AB-200+ but I linked to the search because stock changes. I think if it's faster than 100ns you should be fine.

Heres the processor I got to work, https://www.ebay.com/p/170019433?iid=163333777328
Again, here's the part number in case the link expires, Motorola MC68B09P

There was rumor of a hitachi equivalent but it wasn't pin compatible and would not work without modification. I tried.

If you re-cap the supply be sure to match the temperature rating of the caps 105 degrees if I remember correctly.

The calibration process was pretty straight forward and well documented in the manual. However the firmware of the scope may differ than the manual in a few steps. The manual specifies that the scope will ask for a certain voltage and the scope will actually ask for something else. Keep an eye out for that and just do what the scope asks for. A good precision meter in parallel as specified by the manual is a good idea.

If you have problems post be sure to include pictures of what you see on screen. I'll do my best to help out.


Apologies I meant faster than 200ns. Not 100. The original battery backed chips in my unit were 150. 200 works fine.

Bob Albert

I replaced the NAVRAM modules in my 2440 and the scope stopped working.  I reviewed my work and it looked okay.  I used Chinese chips that perhaps were counterfeit.  I put one of the old chips back (the other was damaged) with no success.  So I have a doorstop.  It's on my list of projects to take another look at it but I am not optimistic.  Power supply voltages are good.

On Thursday, July 29, 2021, 04:59:52 AM PDT, wkibler via groups.io <will.kibler=me.com@groups.io> wrote:

Apologies I meant faster than 200ns. Not 100. The original battery backed chips in my unit were 150. 200 works fine.


Sorry about that the DS1230 is a direct replacement for the DS1235 according to https://www.maximintegrated.com/en/design/technical-documents/app-notes/2/202.html#q13
So you should be able to use DS1230AB-100 https://www.mouser.com/ProductDetail/Maxim-Integrated/DS1230AB-100%2b?qs=LHmEVA8xxfZqkqBXpeOlMg%3D%3D

When I get home I am going to crack open my 2440’s and see what I installed, LOL. It was some time ago.

Be sure you are grounded because that CPU dies when you look at it cross eyed. Be ready to replace it also.