Jun 132016
 

I have a small  Axminster  SEIG X2 milling machine ( the same miller is widely sold under different brands) that is 5 or more years old.   It is a bit wobbly and weak for cutting steel, but I can usually manage by taking small cuts, although it does chip tools occasionally when the work jumps into the tool particularly if I forget and cut in the wrong direction.  For a long time it has had an annoying problem with the motor drive circuit – the speed control potentiometer has a switch to turn the power on, but you have to wait some variable time between switching the pot on and advancing it to run position or it doesn’t run at all.  The delay is a bit variable, between a few seconds and a couple of minutes when its first turned on.  I gather from the internet that this is a known problem.   I’m going to have a go at finding the problem – a timing issue of seconds to minutes that gets shorter as the circuits warm up suggest electrolytic or tantalum capacitors as the source of the problem, but I’ve failed so far to find a circuit diagram of the circuit on the board.   Axminster will sell me a board for £101 but don’t have facilities to repair boards, so I am challenged to find a solution… watch this space as I flounder around……

I took my testmeter into the shed and had a look at voltages – the speed control pot has -5.7 Volts across it, and when it starts properly the voltage stays at -5.7 at all speeds.  If its not starting as you turn the pot, the voltage drops to about -4 V at ‘full speed’ position.  The back of the board is a mass of surface mount stuff, so I’m not sure I can work out the control circuitry – there are a couple of multipin I/Cs that don’t have numbers on them, but I’m pretty sure the problem is in the very first stages of the speed control  – I just need some way of pinning it down a bit….

 

Well, I didn’t find anything wrong, but whatever I did or didn’t do, it is now much better and starts almost instanly 90% of the time – I begin to believe some of the comments on the web concerning bad joints….  A mystery, but since its functioning I will use it and worry when it goes wrong again….

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