You might try posting a question on ASR. John Yang is the user you would want to contact I believe he works for Topping. I know there are a couple of threads where some problems with the A90 are discussed one thing he mentioned was a bad XLR cable can be a cause.
Topping A90 failure issues. Should I try a 3rd A90?
I purchased the Topping A90 & D90 MQA August 2020. The A90 lasted about 3 months then "blew up" with major static in one channel. I tried different headphones, connects (4 pin XLR, 4.4mm pentacon) and it was in fact the A 90. Apos exchanged the failed A90 (took a long time) and after using the 2nd A90 for less than a month, the same issue. So after 2 failed A90's I'm wondering if I try a 3rd or another headphone amp? I'm using XLR balanced (and have 2 headphones that are also balanced cables). Thanks for any counsel.