Hi,

>My experience with at least one ProFile controller which has sockets for some/all chips is that bad connections develop after a while. This causes weird behaviour.
>I have found it sufficient to pry each chip a little bit from its socket (eg. 1mm at each end), and if it still doesn't work, extract and re-insert each part.

>You may find the pins on some chips have become dark or have other signs of corrosion that will need to be cleaned off to get good connections.

>I suppose it may be necessary to replace some/all of the sockets in some cases.

Thanks James,

Yes, the old clean and reseat trick is one of the first things I did when I encountered this problem. You could be right...it could be a socket. These are the same kind of sockets the Apple II+ board uses. I have a couple of the latter and at least one had a socket issue it took me AGES to track down. The other's fault is undiagnosed but I'm pretty sure it's a socket issue as well. Those sockets don't age well!

There are a couple of chips (ULN 2074B) associated with stepper movement I couldn't swap out as I don't have replacements. Checking the logic will be very time consuming as it's quite transient. If I can find a cheap source of these I might order them, just to fully exhaust all leads.

Terry (Tez)