Smart move.
Xin is on the "do not buy from list". Even though it is a mystery why Xin has vanished off the face of the earth, most people who have asked for their money back, have received it. I got mine back in late 2008, and people have reported getting a refund as close as this past Christmas.
So, although I, as a Moderator would highly not purchasing form him until he is back on track (which is stating the obvious, but for nooB's this advice can be quite helpful), he is not a crook, unless there are people who have requested a refund and not gotten it and I don't know about it), but obviously, he is going through a bad patch which has disabled him from being a current amp builder.
But for those of you who need a repair, I would recommend highly, that you do not send your unit back to him, unless you have definitive correspondence with him, and he has assured you a timeline, and no money exchanges hands until you receive your unit back.
Like in the case with Mikhail's amps, others need to be sought out, that are capable and willing to fix a portable.
Maybe someone who has found somebody, can chime in here and make recommendations based upon their own personal experience and not just "hearsay". If Xin has posted his schematics somewhere on the web, then a decent troubleshooter should be able to figure out the cause of the problem (broken trace, bad resistor/capacitor or even a bad charging circuit).