Fix downstream Level on Arris / Nortel Cornerstone CMTS 1000

This is what happens...
just a few days ago we got bad SNR levels and and did not know the reason.
after searching we found that the downstream signal was poor, in the headend.
then we take the measurement of downstream directly on the CMTS (downstream port) and results that was delivering 28dB,
not 50dB like is in the CMTS configuration.

Then i Read this:
This problem is common after 5-6 years of usage and it can be repair, the upconverter (which produces the downstream signal).
This problem happens with Nortel/ARRIS, Cisco and Motorola CMTS units and the good news is that it can rebuild the upconverter
and make it close to brand new again. The components usually last about 5 years before the first failure which cause the downstream
signal to decline or the SNR to get worse.

I am interested in repairing this, I wonder if anyone has knowledge or some notion of how it is repaired. if it would be possible to repair.
I am not taking profit from this, I just would like to fix it myself. the problem is not configuration, should be something physical.

Thanks.