Anritsu MS2711D Spectrum Analyzer: Non responsive Keypad

[aquaman8]

Hi,


I have an Anritsu MS2711D portable Spectrum Analyzer and it powers up and boots the firmware after I press the ON/OFF key on the keypad, but once the the unit boots up, often times the keypad stops responding to any key press or sometimes only certain keys  get a response. No real pattern to which keys remain responsive. Even when the keypad is non-responsive, the ON/OFF key always functions allowing the unit to be turned OFF and ON. I gathered as much info as I could find on the Internet, but Anritsu seems to be ultra secretive with their technical info and no schematics can be found anywhere.


I have mapped out the keypad switch areas (gold plated PCB traces at each of the 28 keypad locations, each consisting of a 'Surround section and a Center section" that are connected together when the keypad location is pressed. The Keypad is connected to the main unit through a 24 pin ribbon cable (P1). There are 8 lines that come from the Center traces of groups of switches on the keypad PCB and the Centers connect to pins 1 through 8 on a TVS steering diode (MMAD1108) located on the PCB. Each of the lines then exits the chip via pins 16 through 9 which then terminate at 8 pins on P1.

Connection of the Surround portion of groups of keys connect directly to the pins on P1. Finally, there are 8 resistors (10K ohms) (pull up or pull down?) on the keypad PCB, with one end of all the resistors is connected to pin P1-3 and the other end of each resistor goes to a separate pin on P-1. Note that the Center and the Surround PCB trace of the ON/Off switch each goes to a unique unused pin on P1 (P1-21 and P1-22). Pin P1-24 is connected to the copper plane on the top of the PCB upon which the switch contacts are etched.


So at this point I understand that

1) this appears to be a typical keyboard matrix with columns and rows arrangement

2) the data lines are protected from over voltage events coupled to the keypad using the TVS

3) Not sure why the keypad becomes non-responsive and 'locks up' but the reason that the ON/OFF key continues to function is because it is not part of the scanned matrix

4) This suggests that the matrix is failing either mechanically or electronically.


So, with this knowledge in hand I now seek direction from anyone who might have some understanding of how the Anritsu keyboard is monitored and controlled to save me time or more importantly to help me avoid causing further damage to the instrument during further troubleshooting. My hope that this might be a common problem with these units and I can zero in on fixing the fault.


My worry is that the keypad scanning is accomplished using I/O ports on the main microprocessor and that these ports may be damaged. Ideally some 'glue' chips or discrete or passive components have failed and it will be an easier fix. Also, perhaps it is a software bug.


Any help or guidance with this problem would be greatly appreciated.


Thanks in advance and sorry for all the detail provided above, but I know that describing a problem as "it doesn't work' is not very useful when asking for help with electronics and I don't want to waste anyone's time unnecessarily.

Thanks for any help of ideas!


Mitch

[drew23]

Hi

I have just bought an Anritsu MG3700A vector signal generator that seems to have the same problem of intermittent keys. Did you manage to fix the problem?

Regards Drew