Help to repair an HP91

[isanchez]

Hi again,
The thing is that I have an hp97 with the same symthoms and I have done the following: I have taken the supposed faulty board and moved into a working 97....and it has worked fine....this means that the problem is in the display...more probably in cathode or anodes?
I am considering that the problem in the 91 could be the same....is it possible to find these anodes or cathode? I have replaced one in an hp67 in the past, and the chip already exists...
Thanks and kind regards

Ignacio