I need an MFA clock guru

I've been fighting with lcd displays all week and not getting anywhere.

I tried a spare set of clocks and eventually the mfa played ball and worked perfectly

Started off like this



Then did this as soon as it was plugged in



But then showed this and then worked perfectly



Now I know the screen is good so I took the clocks apart and proceeded to swap the screen for the one out of my original clocks.

Now I'll try them again tomorrow but if they dont work it leaves me to believe its probably the whole MFA circuit board thats knackered

But my question is will the other circuit board work in my original cluster with the existing blue circuit film as the boards are quite different.

My clocks are the intended items for a 1985 1.8GTI

The donor clocks I think are a set from a 1983 car

Mine have a socket on the back for a small 2 wire plug and the donors dont but it didnt affect their operation in my car

Below are the 2 boards side by side





In both pics the board at the top is the donor one from what I belive is the older set

Also the donor clocks have this but I have no idea what it is



So my questions are

1. What does that knob do?

2. Can I use the older circuit board in my clocks and just leave the small 2 pin plug out

I'm far from being a guru on MFA's but I've had limited experience trying to get the MPG and oil/outside temperatures to read correctly on mine. I haven't succeeded yet either!
What I did find out though is that Motometer clusters are different to VDO clusters, my 1983 GTI tintop has a VDO cluster and I bought a Motometer cluster because the lugs on mine were broken and you can't even swap the plastic as they're different! I also think newer cars use a different way of calculating the MPG.
I'm sure the knob changes it from MPG since you started the engine to MPG since you last did a reset but as mine doesn't display the correct MPG I haven't messed with it much.

Well mine didnt work even with the fully working screen so it must either be either

1. Circuit board itself

2. Blue printed outer circuit

Although both looks fine to me but must be a broken line somewhere