Gah, put this calculator kit together, (same one as mnementh did) and popped the batteries in, the LCD backlight came on, but the calculator refused to switch on
Back to basics, double-checked my work, and it was all correct so measured voltages and discovered that the regulator, 7550A-1 in TO-92 package was only giving out 3V instead of 5V, so I had a chat with Amazon customer support. Explained that I had this kit, assembled it and told them that the 5V regulator was only providing 3V, thinking that they might just send out another kit, so I can swap out the part, but nope. Sent me prepaid returns label and even though it was a kit, going to give me a full refund for it once they receive it back. So, for that I give Amazon full marks. I don't think that I'll bother re-ordering it though, I did a bit of research, and it seems that others have had similar issues with the kit and for that reason, I'll give it a miss.
The PCB seems to nicely silk-screened and of good quality just a shame that the components aren't of equal quality. Instructions are not supplied with the kit
but they are downloadable are adequate for the job as long as you can follow the pictures OK as there is no written description.