On December 23, 2014, Ulli posted the following on time-nuts:

Hi,

I got a used HP 53131A to which I added a stability option board (ocxo).
In order to calibrate the device, a security code is needed - I don't
know it. The seller doesn't know it. It's not the facorty set code.
Advice on how the reset the non-volatile memory would be much appreciated.

Thank you very much & happy Christmas

Ulli

Ulli,

You're right. The actual procedure is not described in the manual(s):

Operating Guide http://cp.literature.agilent.com/litweb/pdf/53131-90055.pdf

Programming Guide http://cp.literature.agilent.com/litweb/pdf/53131-90044.pdf

Assembly-Level Service Guide http://cp.literature.agilent.com/litweb/pdf/53131-90039.pdf

Component Level Information http://literature.cdn.keysight.com/litweb/pdf/5989-6308EN.pdf

But I have three ides for you.

1) The last PDF shows U14 is AT28C64B (www.atmel.com/Images/doc0001h.pdf) so if all else fails, you can use a logic analyzer on the address(13) / data(8) pins and see what's in the EEPROM. With some experimentation by you or others on the list we can locate the calibration security. This has the advantage of getting the existing code, without having to clear the entire EEPROM. Some other HP bench instruments use an onboard jumper to override the cal lock, but I don't see that on a 53131A. So perhaps there is a magic front panel sequence or SCPI command to clear NVRAM.

2) Search for 53132 at http://www.ko4bb.com/manuals/index.php and grab the 4 EPROM's. Do a 16-bit merge of U8/U10 and U9/U11 and look for ascii strings. All the SCPI words are in there and not all are documented. For example near the words SYST and CODE and SEC[URITY] is ALL and DEL[ETE]. Probably safe to try. Lots of interesting output strings, both for GPIB and for internal debugging. Even the words EEPROM CLEAR, along with “Oooh! That tickles. I don't know that vector.” which we also see in the Z3801A, etc.

There's also a hidden “SERVICE MENU”, complete with Easter egg:

 MLB TEAM KRISTI BITTNER, LEE COSART, ERIC INGMAN, GARY JACOBSEN, SOOK-LAN LOH, ROB MITCHELL, ROBIN POSKUS, DON SCHREMP, DANA STOFFERS, AND GEORGE TSAI
SOFTWARE L. COSART G. JACOBSEN S. LOH R. POSKUS D. STOFFERS
HARDWARE K. BITTNER E. INGMAN D. SCHREMP
MECHANICAL G. TSAI
PROJECT MGR R. MITCHELL
BASEHIT -- 53132

3) There's a pForth interpreter in this instrument too. Note pr_eeprom_debug and wr_eeprom.

That's enough hints to keep someone on the list (Magnus?) busy over Christmas. Of course, if anyone knows the “confidential procedure”, they should just let us know…

Thanks, /tvb