Agilent 34970A Error Code 740 - Secure State

[BH]

Hello all,

BACKGROUND:

Recently I acquired a faulty 34970A from Ebay.  The symptom was "Dead unit".  Sure enough, I tried to power it on and it was totally dead.

After some investigation I found that the internal backup battery was totally flat, and that this was upsetting the supervisor IC inside the unit.  I replaced the battery and all good; unit powers on fine.

However...

At power on, the unit was beeping and recording an error.  The error code was 740, which I looked up in the manual and found that it relates to the cal data.  The entry in the manual is:

740 - Cal data lost: secure state

I started to worry that this would mean a 24C02 replacement and a re-cal of the instrument: more than I bargained for! But I started to wonder what "secure state" actually means and I decided to check the Cal Secure settings on the instrument.  The instrument was un-secured, so I secured it with all zeroes for the pass code.  After this, no more errors on power up!
I put the unit back to the unsecure state but still there are no longer any errors on power up.

MY QUESTION:

Does anyone know what the "Cal data lost: secure state" error actually means?

[ManateeMafia]

I believe it is similar to the 3458A when it loses its NVRAM cal constants. The 3458A will display an error "Secure Required".

Basically, you save a new security passcode and the message is gone. It is probably there to warn the user that the calibration lockout no longer exists and someone may be able to tamper with the cal.

No worries once a new code is set.

[HighVoltage]

If the error is gone and stays away, you are good.
If the error comes back you need to replace the 24C02 FRAM because it might be corrupted.
Also, you should check the calibration of your unit. I had one with a flat battery and it had lost some calibration data.

[BH]

Thanks for the replies both.

Fortunately, in my case, the error messages have stayed away.  But it's a stroke of luck that I went down the path of trying out the security code because I was actually gearing up for an FRAM change; even ordered in replacement ICs.

I checked all the measurement options and they seem pretty accurate when compared with my other Test Equipment, so it seems like I have been pretty lucky here!

Many thanks.