HP ESA-L1500A Front panel issue

[little_carlos]

Hi.
I got today this spectrum analyzer and I got issues with the front panel.
The only keys that work are "Preset" from system, the "on" button and the knob for the sweep delay.
The screen shows no issues as it shows all info working properly, and the input works fine since I was capable of doing some small measurements.
I tested the ribbon cable and the cable of the membrane buttons and they show no issue, as well as continuity of each membrane to the connector and they all show possitive results.
Any advice? Would it be possible of connecting a PS/2 keyboard and use it to control the analyzer instead of getting in the trouble of repairing it? the owner manual doesnt show any info of what functions can be accessed with the external keyboard.

Thanks for your time.