Fishbonz: Check my logic on this and see if you agree. I'm thinking that there's a 3rd layer to this board that we're not seeing, and it might be a ground plane among other things. U1 is an LM324 Quad Op Amp, and U2 is a CA339E Quad Comparator. I can find a VCC+ connection to both chips, but I can't see visible VCC- connections for either chip. Do you see them? The speed pot connections are Wires 53, 54 and 55. Wire 54 appears to be connected to speed pot center pin which would be the wiper. The other 2 pins on the speed pot I'm going to call the speed pot max, and the speed pot min. Those 2 connections should be connected to the MAX SPD and MIN SPD trim pots on the board. I'm going to assume that Wire 53 will be connected to the minimum speed side of the speed pot and Wire 55 will be connected to the maximum side. To verify this we could connect an ohmmeter between Wires 53 and 54. At minimum speed we should be reading 0-ish ohms, and at maximum speed we should read 5K-ish ohms since. (If it's a 5K ohm pot like the book says.) I don't think they kept the speed pot connections grouped together on the terminal strip on this drive like they did on the other drives. It looks like T8 is connected to the MIN SPD trim pot on the board, so that would suggest that it should be connected to the minimum speed side of the pot - wire 53. T7 is where the +10V was found so that would suggest that this is speed pot maximum side connection - wire 55. One would think that T7 should also be connected to the MAX SPD trim pot, but I'm not seeing the connection - maybe on the 3rd layer? It DOES look like T7 is connected to T6 by a jumper labeled W1 located between the terminal board TB2 and the trim pots. Was +10V also found on T6? Would the speed pot wiper connection head towards the firing circuit for the SCR's, or toward the Op Amp? I would guess the SCR's, but I haven't dug into it enough to know. What do you think? Don
