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The wiring harness

December 10, 2011

Today I took on the relatively arduous task of mapping out the wiring harness as it will need to be totally replaced. Fairly large portions of it are severely burnt/melted, more than I had initially noticed/assessed. For the most part it it is fairly straight-forward point-to-point connections. I started with the door sensor loop, as it is the most damaged.

Door Sensors & Bypass Circuit:

CTL[13] --- + --- <RSL> --- <LSL> --- + --- <RSD> --- <LSD> --- CTL[9]
             \                       /
              \ --- --<     >-- --- /
                 Lid Sensor Bypass
RSL/LSL: Right & Left Side Lid sensors
RSD/LSD: Right & Left Side Door sensors

As you can see the magnetic door sensors are simply connected in a loop. There was a mystery connector on the top of the chassis, as it turns out this is used to form a bridge across the lid-door sensors, effectively bypassing them to allow operation with the door open. Unfortunately I had to destroy this connector to remove it, so I will need to find a suitable replacement. [I didn’t have the bridging plug anyway]

Next up is the connections to the front panel. I had initially assumed the mystery RC on the control board was for debouncing an input from the wiring harness, but as it turns out it is a straight connection from the main controller to the front panel. So the purpose of the RC remains a mystery for the time being. The connection is a standard IDC ribbon cable [26 pins].

Another unknown [but assumed to be for the rotary attachment] was a completely melted DB9 connector. Once I unbundeled the harness, I was able to confirm that it indeed was for the rotary attachment, as one set of wires went to the stepper driver, and the other to the main controller.  I was able to determine a pin-mapping, but don’t know the function of each line yet. Although the insulation was burnt off, and the connector was melted beyond use, the bare copper of the wire remained, and all the wires appear to have remained in their relative positions.

Rotary Attachment Connector:

1 - Stepper   6 - Stepper
2 - Stepper   7 - Stepper
3 - N/C       8 - N/C
4 - Homing    9 - Homing
5 - Homing

Next I Mapped out the Stepper driver connector, which is a 20pin ATX power connector style connector. The connections are as follows.

 1 - Rotary[6]           11 - Rotary[7]
 2 - Rotary[2]           12 - X[5]
 3 - Rotary[1]           13 - X[6]
 4 - Shield [Rotary]     14 - X[7]
 5 - Shield [X]          15 - X[8]
 6 - Shield [Y]          16 - Y[3]
 7 - Shield [Z]          17 - Y[4]
 8 - Z[1]                18 - Y[2]
 9 - Z[6]                19 - Y[1]
10 - Z[8]                20 - Z[3]

I will need to analyze the stepper driver board to try and determine the wire parings for the motors. Though I may also be able to derive it from the stepper datasheets I can find. Though given the pinout, I am imagining its:

Axis   PhaseA  PhaseB
Rotary  1&2     6&7
X       5&6     7&8
Y       1&2     3&4
Z       1&6     3&8

I’ve confirmed the Z pairing via the datasheet. The motor side has jumpers between 2&6, and 5&7 placing the coils in series for bipolar operation.

The remaining wires all run to the same 34 pin connector [J4] on the main controller board. This connector contains the LASER control, safety loops, and homing & limit circuits.

 1 - CO2 Modulation     2 - Opto Return (Modulation & Diode)
 3 - LASER Diode        4 - N/C
 5 - AIR[5]             6 - AIR[6]
 7 - AIR[2]             8 - BEEP[1]
 9 - DoorLoop          10 - BEEP[2]
11 - INT[6]            12 - LASER Interlock Out
13 - DoorLoop          14 - INT[5]
15 - N/C               16 - N/C
17 - AIR[8]            18 - VCC (XY[3])
19 - GND (XY[4])       20 - LIM[2]
21 - GND (ZLIM[4])     22 - N/C
23 - XHOME (XY[1])     24 - N/C
25 - YHOME(XY[2])      26 - GND (ZLIM[2])
27 - LIM[3]            28 - LIM[1]
29 - Z-LIMIT (ZLIM[1]) 30 - VCC (ZLIM[3])
31 - Rotary[4]         32 - Rotary[9]
33 - Rotary[5]         34 - N/C

I forgot to map out the Z axis limits board (ZLIM) so I’ll need to do that to determine their final functions. [I’ll come back and edit this post once I get a chance to do so]

There’s a trio of unknown connectors I’ve labelled as AIR/INT/LIM; I’m assuming these are for the Air-Assist option. The connectors were present on my harness, but not attached to anything else, with the exception of the INT connector which had a small loopback plugged into it for two of the wires [5&6]. INT and LIM are bundled together, and were located in the back right corner of the unit inside the engraving chamber. AIR and a 48V power connector were located on the bottom of the unit below the laser & electronics [outside the engraving chamber].

The INT/AIR connectors also have a set of wires that runs between them as follows:

INT / AIR
 1     7
 2     1
 3     4
 4     3

Based on the pattern within the main connector, I’m guessing that INT 5&6 form some sort of safety/interlock loop like the door sensors do. [hence the reason they are looped together]. The LIM connections appear to be another set of limit/homing sensors. So perhaps this is not for the air-assist option as previously thought, as I cannot think of why we would need en extra safety-loop and limit detector for air-assist. Though if it’s not for air-assist, I have no idea what it could be for.

The final connector, is the one on the back of the LASER itself. The pinout for it was pulled from a ULS OEM LASER manual.
LASER Pinout:

1 - +48V    4 - N/C           7 - GND       10 - N/C
2 -  N/C    5 - Interlock In  8 - +12VOut   11 - LASER Diode
3 -  N/C    6 - Modulation    9 - RET       12 - N/C

Note that the pinout does define additional signals, but I’ve only included the ones connected in my harness here.

Actually there a re a few more connectors, but they are for power, which is straight forward. And the two break-outs for the back panel connectors to the mainboard, which are of no consequence here.

[Update]Added the Z-limit signal assignments. The board is arranged differently than I had imagined. I had assumed the two LED’s would have been in parallel, and each limit would have had a discreet output, given the 4 pin connector.  But the board is actually arranged such that the two LED’s are in series, as are the two photo transistors. In this arrangement if beam is broken at either detector the sense loop goes open circuit. The only downside to this arrangement is that you have no idea which side was broken, but one can extrapolate that from the direction of motion. [assuming everything is set up correctly][/update]

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