How can this 2465b be working at this age?

[MarkAlfaspider]

I have a Tek 2465B which needed a bit of repair to the A5 control board, as it had the usual leaky cap corrosion issues.  Got it repaired and
running, and it passes all the self-checks including cal. How is that possible? The Dallas module I thought would be long dead by now-?
The date code on it was 1990, and I'm fairly certain it's the original board with all OEM parts. Any thoughts?  I assume it's on borrowed time...tick, tick
Mark

[dpyinhao]

You won the Dallas NVRAM silicon lottery! 1990 is incredible.

But seriously, dump the cal constants right now before you turn it off again. Once it's backed up, drop in an FRAM mod or socket a new NVRAM. You don't want to go through the nightmare of a 2465B manual calibration from scratch.

Great work on the A5 recap repair!

[TERRA Operative]

I have all the equipment to perform a calibration, and have done so on a number of these and related scopes.

Listen to dpyinhao, he speaks the truth.....

[Tation]

A few years ago I replaced the Li-SOCl2 cell of my 2465B by a new one (in a different shape, used a wired adapter), just to be safe. After that I discharged the original cell measuring its remaining SOC. Well, after 30 years it was still at ~50 % SOC, amazing.

[MarkAlfaspider]

I thought the Dallas 1225Y had to be removed from the board to read it? (risky) Is there another way to read the contents?
M

[TERRA Operative]

You can apparently read it out via GPIB if your scope has that option, and I've read there is a way to step through the cal constants on screen so you can write them down on a piece of paper.

[MarkL]

I thought the Dallas 1225Y had to be removed from the board to read it? Is there another way to read the contents?
M

Two ways:

1) The easiest way is to take a video while using the "EXER 02" service utility to step through the calibration data on the screen.  See the service manual on how to get into and operate this utility.

To put the constants back, you can use this utility:

  https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg5513656/#msg5513656


2) If you have the GPIB interface on the scope and a host interface, you can dump the calibration constants (and put them back) as in this post:

  https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg4750262/#msg4750262


I would not recommend the FRAM replacement.

EDIT: Fixed wrong link.

[TERRA Operative]

I would not recommend the FRAM replacement.

Why not? I have done a few upgrades and they all work fine. Many others have had no issues with FRAM too.

[MarkL]

I would not recommend the FRAM replacement.

Why not? I have done a few upgrades and they all work fine. Many others have had no issues with FRAM too.

I only know one case where it didn't work.  It works for almost everyone.

The 2465B and other scopes in this series were designed to support the power up/down requirements of the Dallas modules in order to guarantee stored data integrity.  The FRAM power up/down control signal requirements (/WE and /CE) in relation to Vcc are quite different and not implemented by the host circuit.  The FRAM works in these circuits by chance and not by design.

https://www.eevblog.com/forum/projects/dallas-ds1245-replacement-by-sst39sf040/msg6301316/#msg6301316