I would not buy a replacement for U400 without making sure that yours is bad first.
If you can wait while yours is tested, I'd send it to the Seller on eBay who sells them for $170. ?He will test yours for $5, plus the cost of return shipping.
He also has a warranty on his used U400 if you choose to buy one and the $5 testing fee can be applied to the price of a replacement U400, if you buy one..
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