the "no problem / sorry" pattern is the most typical Chinese traders behavior!

The point is that manufacturer under no circumstances sell spare hash-boards without returning the full defective unit;
they only manage replacements as they DO NOT own an equipped lab for repairs;

So, the only option is claiming warranty to your vendor by sending back the full unit;
Upon receive from you, the vendor ship the miner to DaYun that should replace the faulty boards, provided that have not been burned out by overclocking, surge or else... but as they are definitely unable to understand the failure cause, the decision in totally arbitrary!

Looks to be big challenge even for Chinese customers, good luck mate!

FYI, my CN partner investigated and explained the whole workflow:
1) the ASIC chips and PCBs (main / hash boards)  are produced by a well known high-tech factory in Shenzhen area;
2) the DaYun manufacturer (most likely based in NingBo) is a very small company just managed to buy and assemble the raw material, develop firmware (maybe...) and distribute the end product to the myriad of vendors mostly located (again) in Shenzhen...
3) the vendors are the only "official" distribution channel and they all signed an agreement with DaYun to not unveil their identity!

/E