HP-25 - what could be wrong, simple question

[PANAMATIK]

The HP-25 stores its 8 registers, 49 program steps and the LastX register in external RAM 1820-1564
If the registers always show 0.00 values and program steps show 13 00, and the RAM chip is already replaced, there could be a disconnected DATA line pin 11 of the ACT. This serial data line reads and writes from the RAM chip. if there is no interruption, it must be assumed, that the ACT has a defective DATA pin.

Bernhard