X motor PCB’s

December 6, 2011

Almost forgot, there is a pair of small PCB’s that need to be mapped… The PCB that sits over the X stepper motor, and the one that connects the flex cable to the main wiring harness. For all intents and purposes these two PCB’s can be thought of as a single PCB, and that’s how I’m going to handle them [it looks like ULS looks at them like this as well, based on their component designators]. The main wiring harness plugs into the lower PCB which is bolted to the chassis. This PCB simply passes the signals onto a flex cable, that runs the signals up to the upper PCB, which then breaks them out for the X stepper motor, and the X & Y homing sensors. With the exception of a handful of capacitors, and a couple of resistors, there really isn’t anything to the PCB’s.

The mapping works out as follows:

 Lower PCB       Upper PCB
J1    Flex1     Flex2    J2
1       1         8      X Homing (Q1 collector)
2       2         7      Y Homing (Q2 collector)
3       3         6      VCC
4       4         5      GND
5       5         4      4
6       6         3      3
7       7         2      2
8       8         1      1

On the lower board, there are 3 small capacitors on the signals for pins 1,2,3 going to ground [pin 4] (C1,C2,C3 according to the PCB designators)
On the upper board there are another 3 small capacitors on the same signals (now pins 8,7,6) going to ground. (C4,C5,C6 according to the PCB designators)
From Pin 5 (3 on J1) [which I am assuming is VCC] there are 2 series resistors (R1 & R2), which then run to each of the beam-break detectors (Q1 & Q2). [presumably the LED anode]
The LED cathode of each beam-break detector goes to ground [pin 5 (4 on J1)] which is a solid plane on both boards.
On the other side of the detector, the collector runs to the connector, filtered by a capacitor, while the emitter is tied to the ground plane.

In this configuration, the signal for the homing sensors must be pulled high on the controller board. As long as the light from the LED makes it to the transistor in the detector, the transistor will be conduction, effectively pulling the signal to ground. When the beam is broken/obstructed, the transistor stops conducting, and the signal floats back high.

The values for R1 & R2 are not important, they are simply calculated on the voltage, and the current the LED’s require [likely in the ballpark of 150 Ohms in this case for 30mA@5V]. The values for the capacitors are also not all that important [most likely 0.1uF]. Q2 is missing, and Q1 is badly melted, but I can derive some sensible part numbers for them.  Firstly Q2, it is larger than Q1 and appears to be the same size as what issued on the Z axis limits board, which is perfectly intact. So going on that assumption, Q2 is a EE-SX1042 5mm photointerrupter. Working the pinout back, it coincides with my assumptions above, so it appears to be correct. Q1 is smaller, measuring the gap it looks to be about 3mm. I can also make out the digits 1025 on the side. Assuming the same family as Q2, I manufactured a potential part number of EE-SX1025, which according to Digikey is a 2.8mm photointerrupter… A hit! Once again the pin-out lines up with my earlier assumptions in decoding the circuit. I don’t know the mapping for the final 4 lines, all I know is that they are the stepper motor coils, I’m assuming 1&2 are one coil, and 3&4 are the other.

There is one final component on the upper board, it is a spring loaded plunger that is used to break the beam of Q1, as the X carriage does not have a flag, like the Y axis does. This plunger needs to be salvaged & restored. Luckily it is machined out of aluminum, so should restore just fine.

So with that, I get a BOM for the two PCB’s as

C1,C2,C3    0.1uF
C4,C5,C6    0.1uF
R1,R2       150R
Q1          EE-SX1025
Q2          EE-SX1042

In other news, still working on second-sourcing the other mechanical bits, but have not had much luck. I also looked into second sourcing the optics, I found some options that may work, and are possibly higher quality, but doesn’t look like I’d really be saving anything there. Though may be an interesting option for home-rolling my own HPDFO upgrade, which is $3000 from my ULS rep.


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