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I'm a newbie restorer. Just put an alltek mpu into a stern nineball along with new driver and rectifier boards, repinned the driver brd, rectifier brd & two left plugs on the mpu. Will do them all eventually. Currently, game boots up fine but can't start a game, nor go into diagnostics from the front door switches. Can do self tests from the alltek mpu board. I am thinking it's maybe a continuity problem with the door switches or a switch matrix issue. However, i just want to check i'm not missing something. On boot up i get the image attached - 21 credits, don't know what the 27 or 600 means. Next step is finishing off the repinning.

Yep, followed everything in the alltek manual including setting dip switches & a memory clear. Test points are solid 4.95V and 44V. Thanks for the tips, I'll check the common wire on the door.

@pinbilly, thx for yr advice. Yep, jumpers are on left. Don't know if i have sound yet, it may yet prove a problem because at present i just get white noise in the sound test.

Thank you @superchicken for the tip and photo re block connector, i hadn't thought of this. Thanks for taking the time to take a photo, i didn't know that thing was called a block connector!

Thx so much everyone, you have been a great help!

The machine is at a mate's place and I'm waiting for him to find time for me to come around and work at it. I'll post the solution.

OK, this problem is solved, and I am embarrassed to say... there was no problem. All the game needed was a ball in the ball trough.

So now the NB is playing like a dream. Thanks for all the advice, I've learnt a few useful things from this thread. (BTW The '600' in the image in my OP was the default high score.)

The good news is this Nineball is playing like a dream now. It's a great feeling to bring back a machine from the dead.

(I've got a problem with the 6 target spotting as soon as the 5 target drops, ie goes straight from 6 to 8, I'll take a look at that later.)