You can try to run the hashboard with a different (higher) frequency with Braiinos
You can run it from a micro SD, only for the test, and after that you will be able to use the stock firmware again when you remove the sd card

I had some dead hashboards with Antminer S9j, S9 and R4.
In most cases Braiinos helped a lot, I cannot really explain why but to modify the frequency gives very nice results.

Please carefully read the readme/github of the firmware Braiinos before doing any major change in the settings