Help! I bricked a perfectly functioning 2467B!

[vintageradiobuff]

Hello all,

I have posted this on the Tek group on groups.io, but I am posting it here too for a wider audience.

I had a perfectly functioning 2467B scope (1989 vintage). After reading about possible loss of calibration data due to the NVRAM battery dying, I decided to put in a new battery (mine is the older version, below 50000 serial #) which has the battery separate from the NVRAM. The battery had a date code of 2689, so the battery is 35 years old. I did hook up a backup battery before removing the Lithium battery and confirmed that pin 28 of the RAM chip had at least 3 V on it from the backup battery after removal of the original battery. After putting in the new replacement battery, I also changed out the 4 electrolytic capacitors on the A5 board. When I put the scope back together and fired her up, I got the dreaded " Test 04 Fail 13" message indicating corrupted or lost calibration data. Not sure how this happened since I hooked up a backup battery before removing the original battery. So, the very thing I was hoping to prevent happened by my being proactive!

Before doing all this, I had made a copy of the RAM contents by running through the Exercise 02 option, so I have the original calibration data available. My question is: how to write this data back to the RAM?  (my scope does not have the GPIB option).

I look forward to your suggestions and hope to get this fine scope functioning again!

[alpher]

Can't help you with writing to ram, (went through the same ordeal as you a few years back) . But nonetheless my advice, don't be affraid of "calibrating" the scope back.
Since you didn't change any parts nor moved any trimpots all you have to do is to go through is a couple of CAL procedures, even doing it first time in my life it took me ~an hour and a half.
Not hard at all. CAL-1 and CAL-2 if i remember it right, and of these only the first one takes any time.

[colorburst]

I like Mark's suggestion to write cal data using customized firmware. Sounds like he already wrote the program, so all you'll have to do is burn a set of EPROMs and temporarily install them in the scope. Hopefully they're not soldered down!

[DavidAlfa]

No sense, you need a programmer to burn the eeproms, then just program the nvram in it!

Same happened to me. It was working, but after replacing so many exhausted NRAMs I decided to make a preventive maintenance, however it died after desoldering and placing it into the programmer.
But you'll need a programmer. Though a SRAM is very easy to interface, any Arduino, AVR, PIC, STM32 board with enough pins will be ok.
Try writing the data you got from EXER02 to 0x1FE00 - 0x1FFFF.
I recall doing this, but not 100% sure, I ended making a complete recalibration, everything was way off after 30 years.

https://www.eevblog.com/forum/index.php?topic=5397.msg4747154#msg4747154

[colorburst]

No sense, you need a programmer to burn the eeproms, then just program the nvram in it!

OP mentioned their model has an external battery, so the SRAM needs to be programmed while installed in the scope, unlike a Dallas block.

[DavidAlfa]

Ah, sorry, missed that detail.

[MarkL]

So, the mentioned firmware utility to restore the EXER 02 data is done.  If you're not a watcher of the big 24xx thread, it's been posted here:

  https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg5463367/#msg5463367

[colorburst]

Thank you Mark and Don, great work! This closes the loop on cal data woes for 2400 A/B scopes.