There are many different versions of an automatic antenna tuner on ebay and other sites. Some come with a case while others are supplied as a PCB and a bag of parts. There are few instructions around but there are circuits diagrams, or schematics, on some sites.
I ordered what I thought was a complete PCB with case but what arrived was a populated board without a case. I complained that it was different to the photo for the item and accepted a partial refund which amounted nearly what I paid. I then ordered the case for under £13 post-paid.
The board came with SMA sockets already attached which meant it would not fit in the case, so they were removed. Assembly was a bit fiddley, but all seemed to go well. The first power up showed the screen was working. Next came an RF test which did not work. Some quick tests showed that the rear panel had no earth connections to the PL259 sockets!
I decided to make a new panel from aluminium. After reassembling the case and testing with a TX connected to my long wire antenna everything worked as it should.
I now have an fully automatic ATU that senses when there is a band change and retunes.