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!