Thanks for the reply. I got an 8gb card from my friend’s Pi, put the same image on and it worked fine. I then copied that image over to the 16gb card, and at first it seemed ok, but then it crashed with a “bus error” so I decided the card was bogus. I got a replacement card from the seller, and had my suspicions confirmed. The new 16gb was even slower in h2testw, with a write speed of just 3.4 MByte/s. I formatted it and it said it was a 60gb card! So definitely something suspicious. Serves me right for getting a cheaper card!!
So anyway I’m up and running with a decent card now, on v3.6. The whole retropie experience is great!!! I just need to sort out the controls now…thinking of getting an old style microswitch arcade stick and some buttons.