I sometimes use the word "spot check" at work. When we write a report and have a lot of tables in it, we want to make sure that numbers are all correct. I ask someone to take a look and see if everything looks correct. I may ask someone to do a spot-check, which means that I am not expecting my colleague to check everything.
I helped You (his name) with his pronunciation earlier today. I realize I did do a through check while I was helping him (so it was not exactly a spot check). I was helping him to keep a poker face with any sounds, consonants or vowels. Especially he needs to be careful with some vowels like U and O. Japanese people tend to use rounded lips for these two and when they do they sound very Japanese (it's subtle).
The trick is to smile and produce these sounds while half-laughing. When you laugh, the throat/neck will relax and with that you will be able to articulate sounds well.