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Well I managed to secure the new replacement speed control module – yippee!!. My sincere and grateful thanks for pointing me in that direction Techman. It does indeed look like it will marry up with the projector’s multiconnector. Not quite sure how to orient it yet (not much wriggle room to say the least!), but that’s to come.

So before I take the plunge and try to install it, I want to have another play with the existing one and report back here. I also wanted to try and sketch out the circuit for this new replacement in an attempt to understand how it works. I must confess to getting myself in quite a mess when trying to trace things out though, and the result is a rather spidery and perhaps not as logical as I could be (sorry), but hopefully it makes some kind of sense to someone. I should of course be very grateful if anyone can point out any obvious stupidities and also help to explain how it works.

I’ve also produced a component listing, although some components are difficult to identify – some diodes (D2-D4 incl) and a green component marked TNR, G820k, 4X1 or TNR, 6820k, 4X1 (Z1). Again, if anyone knows what these might be, I should be grateful to hear from you.

If this module does the job, I’ll feel happier about trying to un-pot the original. I’ll try to sketch that one out too (assuming it’s not all one big IC of some kind). I must confess to being staggered by the dramatic difference in size between the old and the new. I have no idea how Bell and Howell got everything inside the potted version!