Dead Model F - faulty sense amplifier?

[Matze]

Hi,

I try to fix a dead Model F XT. I was measuring and poking around. When the sense amplifier is installed, the pins 27-36 on the 8048 do not generate proper signals, without the SA everything looks fine on these pins. All other passive components running within their specs.

Before it was completely dead, the keyboard produced random button presses or was not reacting at all. Now it is completely dead.

Does someone faced this behavior before and could give me an advise how to be sure it is the sense amplifier?

Assuming the sense amplifier is dead and need replacement, does someone have the 8273565 for sale or knows a modern replacement circuit?

Thanks in advance
Matze