GW Instek LCR819 and the mystery of password

[pico61]

Recently I purchased on Italian version of well know auction website a GW Instek LCR-819.
This is a lcr meter with excellent characteristics, with a basic accuracy of 0,05% and a max frequency of 100 kHz. Then, the selling price was very good.

A few days after the purchase I received the instrument which was in good condition, although quite used.
After switching on it, I tried to measure some precision resistors, capacitors, inductors and the resulting values was in the specification. But when I tried to calibrate the instrument with the open / short procedure, with great surprise I discovered that the instrument asks for a 4-digit password. Strange thing since the manual makes no mention of passwords on calibration procedure.

I contacted the seller asking if he knew the password but replied that he never tried to calibrate the instrument. I searched the internet for the service manual but with poor results. It seems that GW Instek does not disclose the service manuals of its instruments. Bad practice now common to all manufacturers.

Then I contacted the GW Instek support asking if they knew how to reset or skip the calibration password. The day after I received the answer. A support technician apologized but said that they cannot disclose any calibration passwords. Thinking to be misunderstood I rewrote specifying I didn't want the password to recalibrate the instrument but only that for the open / short procedure, provided in every lcr meter. I had no new answer!

I opened the instrument and looking carefully at the printed circuit board, I discovered there was an eeprom, a 93C66. I thought that the password and perhaps some parameters of the instrument were stored inside. I unsoldered and read it with my programmer but unfortunately the memory was empty. After I discovered that it was necessary to memorize the 100 settings of the instrument.

I think the instrument belonged to some company that made the firmware change to avoid the modification of the residual parameters by those who worked with it.

I also tried to activate a secret menu during boot. And I discovered that pressing the "-" and "7" keys the screen turns completely white with a flashing cursor that requires a 4-digit password. After entering the fourth digit (certainly incorrect) the initial screen reappears. The GW Instek technician was probably referring to this password in his answer.

First question: is there any forum user who has had such problems with the GW Instex LCR-8XX series of lcr meters?

Typing 10000 passwords is unthinkable! Already after entering about 400 passwords I got tired.  And then it's not an electronically elegant solution...
I thought of using an Arduino board and several relays that simulate the keys pressed. Searching for the password with "brute force". I would visually check the unlock.

Second question: has anyone ever used such an approach to solve a similar problem?

Otherwise having a copy of the firmware of another tool I could try to copy it to mine. There is however an oddity. On the motherboard there are two sets of eproms. One soldered and the other mounted on a socket. One for the firmware and the other for    . Perhaps for the calibration data?

Thank you all for the answers!

[nctnico]

Dang it! Your message made me look on Ebay, low-ball offer the slightly higher end model and the seller accepted 
Then again... I feel a project might come up for which I can put it to good use.

Looking at the user manual the calibration menu doesn't look like the right one for the open/short calibration. You are likely in the factory calibration menu.

BTW: did you check the voltage of the Lithium battery? According to the manual the user calibrations are stored in a memory supplied from the battery. It seems you can keep the calibration constants for various component test fixtures.

[AVGresponding]

The offset menu is the one you want for zeroing the leads.

I have the Iso-Tech version, and iirc I downloaded the manual from RS, but I'll link it here as well.

[coromonadalix]

I contacted the seller asking if he knew the password but replied that he never tried to calibrate the instrument. I searched the internet for the service manual but with poor results. It seems that GW Instek does not disclose the service manuals of its instruments. Bad practice now common to all manufacturers.

They protect their intellectual properties ....... if they haven't copied it from someone else  loll

[pico61]

low-ball offer the slightly higher end model and the seller accepted 

The instrument had been on sale for a long time and nobody bought it ... and then it was listed with best offer. Why not ask for a discount?

Looking at the user manual the calibration menu doesn't look like the right one for the open/short calibration. You are likely in the factory calibration menu.

Yes. Sorry!    You are right!   
I have to learn to read the manual well before asking stupid questions!

The offset menu is the one you want for zeroing the leads.

I have the Iso-Tech version, and iirc I downloaded the manual from RS, but I'll link it here as well.

Is true. I apologize to everyone! 
I confused the calibration menu with the offset menu.
I tried to zero the meter with the offset menu and it has completely zeroed the residues.

Thanks to all for watching and for answering.