Axis Control Part 2
Training on the axis controls of the STA Compact, part 2: DC Motor Driver Board. Part 1 can be found here.
Axis Control Part 2
On to the DC motor driver board…
Power slides for this board are 5volts and 25th 6 volts, the main fuse is F1, & the general functions for this board is to control the DC motors.
Needles 1, 2, & 3 on the pipetting head (which is arm 1), the z movement of arm 2 (which transports the cubets), in general the DC motorcontrol board simply controls the z movements. It’s also the main board for liquid level detect.
Liquid level detect are analog signals coming from three needles, and it’s generated by the multi-function pipetting headboard, transmitted by means of current moves to the DC motor-board.
Let’s go through the supporting LEDs on this board.
The Green LED 1: is simply telling you that the microprocessor is working
The Red LED 2: is again from the central PC telling you this is basically functioning
The Green LED 11: tells you the onboard 5volt power supply is correct
The Red LED 12: if this is on it tells you this is the reset signal
The Yellows, LED 7,LED 3, LED 5, & LED 6: are all home position of the z-movements
The Green LED 10: on means there is liquid level detect activated
LED 9: if it is on tells you there is liquid level detected for needle number 2
The Green one, LED 8, is for needle number 1
Simply touch the needle and you will see this light come on and off, you will also see the light come on and off on the pipetting headboard (this is worth looking at because it is a common issue).
In general the functions of the DC motor driver board are to control the z movements of needles 1, 2, and 3, and on arm 2. Also the liquid level detect for needles 1, 2, and 3. Any other issues with this board I can’t honestly say I’ve seen. I’ve never seen this board blow any fuses, though I suppose that is possible. The biggest fault on this board is Liquid Level detect not working. Liquid Level detect as far as the circuit board is an intermittent problem, it pretty much won’t work all the time for a specific needle.
Let’s talk for a second about the pipetting head, getting these three boards together. The pipetting head board, the pipetting head heating board, & the multi-function board are all located on the pipetting head. The reason why we are going to talk about all three of these together is because they share many functions and there is many signals between the two.
The connection headboard in general just directs the current to the z movements for needles 1, 2, & 3.
The pipetting head board heating has one LED yellow dial on it and it simply says that the 26volts is there, it is powered by 5 volts, 12 volts, -12 volts, & +26 volts.
For the most part all this does is heat needle number 3 block, it has a lavender resistor to tell you what the temperature of that block is. It also has the Y home position for the pipetting head.
The multifunction pipetting headboard (which is the bottom board) is the key board here.
The reason I wanted to discuss these all together is because of one potential problem with these three boards. Typically needle number three will get a leak on the top of the needle; you will not be able to see that leak in general, and you will not see the damage simply by looking at it. If you put your finger over the needle, or turn it a certain way you may see a leak in the top of that tubing, another way is you may see drops coming from needle number three.
Bottom line is this: when needle 3 leaks at the top, that solution comes down and goes on the connector that is underneath the connection headboard
From there it drips on down and moves its way to the heating board, from there it gets on the multi-function headboard. Ticks off all three boards. Fairly easy to get to all three, but generally, all three are replaced together.
You might get away with not replacing the connection headboard, but I can almost guarantee you that the heating headboard and the multi-function board are pretty much destroyed if this should happen
General indication of this would be: Liquid level detect not working, Y movement doesn’t appear to be working (in other words you might get needles crashing), and a lot of times needle number three temperature will be out of spec. If you get needle number three temperature out of specs, I can almost guarantee you that is the issue (head number three doesn’t go out of spec temperature for any other reason, assuming someone doesn’t misadjust it). But for the most part, if you see any of those malfunctions, be suspicious of this area. It is not hard to take the boards apart, and once you take the boards apart the damage is very easily seen.
Back to the multi-function board: tensiometer feed one is on the pipetting headboard, this controls the temperature for needle number three (which we will talk about later). There are also some diodes on the board, yellow LED 4 says the Y1 home position is detected. Take the arm, put it all the way back to the back, there is a little steel slot on the side of the pipetting headboard it goes through the zero detector, and LED 4 yellow comes on. Green LED 1, if it is on it means your Z1 arm position is detected, you need to take the pipetting head and move it back and forth, and when you get it in its proper z position that light will come on. The red which is LED 5 is the liquid level detection for needle number 1, when you touch that it should come on. LED 2, which is green, comes on if the z2 home position is detected, in other words needle 2 home position. Put the needle all the way up and that LED will come on. The red which is LED 6, here’s the liquid level detect for needle number 2, touch needle number 2 and LED 6 should come on red. LED 3, which is green, if it is on z3 home position has been detected, move the needle up and down, z movement (by the way sometimes the z movements will move easily, depending on what state the instrument is in, and sometimes they will not because they are being driven). Red LED7 is on for the liquid level detect for needle number 3.
All of these liquid level detects are worth paying special attention to during the endurance, one of the common problems with this section is that the liquid level detect light doesn’t come on. There are several reasons why this can be, most common is that the liquid level detect wire has come off, second reason is that the liquid level detect wire is broken, third reason could be that you have water in the z tubes (in other words you have a leak and water has gotten into the z tubes, if that happens liquid level detect will not work). At this point I will tell you that if you just bleached the system you need to make sure that bleach is removed, because bleach will make the liquid level detect not work, that’s another common problem.) And of course as I mentioned earlier water getting down from a leak onto the pipetting headboard will cause a liquid level detect issue.
So those are the common problems for that. But it is important to watch them, especially during endurance, & it can be very intermittent, and you watch these and watch to see if the light comes on before the needle actually goes into a (reaging?) bottle. If you see the needle go down and it doesn’t go into the bottle, it stops at the top and the light comes on, that’s your problem. Very very common.
That can be caused by any of the functions I just mentioned…
At this time I will also mention that the z motor sometimes a gear can become loose, and that will cause it not to go all the way down, that does some funky things, if you have a needle crash that can by why that happens.
The pipetting head – The pippetter, I will tell you I see very little problems with the pippetter, in fact I can tell you I have never seen anything with the pippetter that caused failure other than it being dirty. It is very easy to clean the pippetter off, I suppose I’ve seen a couple of motors fail once in a while but for the most part they are pretty steady.
I can’t remember replacing a zero detect board, ever.
Stepper motors, meaning for the x/y movement, very seldom do they give you any problem. This is a pretty solid instrument, I can’t remember ever replacing the one, I think arm 2 I’ve seen the gear strip off maybe once or twice in 10 years.