Weird Saturn model 1 issue, no startup animation, disc spins but it won't read

I got a US Model 1 Saturn from eBay yesterday. The seller said it had been tested with games and was surprised that it didn't work.
Anyway, he gave me a full refund but I'd still like to get it working.

When I turn it on I don't see the startup animation, it goes straight to the static Sega Saturn screen and then goes to the CD player saying "Checking disc format", there are 2 green cubes on either side.
The disc spins and the laser is shining red, but it never actually plays a game disc or audio CD. I've tried adjusting the pot and lifting the spindle, with no luck. When I google these symptoms it only comes up with issues users are having with mod chips. There is no mod chip in here. In fact it looked like it had never been opened before.

It's really got me stumped. I was going to order a new laser unit, but then I realised that there should be a startup animation when you first turn the unit on, so thinking something else is wrong.
I tried reseating all of the cables, etc

Thanks

 

Nobody has any ideas?

 

Have you tried using a different ribbon?

 

No, I don't have one unfortunately. I might have to get a working Saturn to diagnose this one.