Aixun T3A Front ESD Protector Filter

OVERVIEW
 

Please read entire description before attempting this project!

This is a protection circuit and enclosure for the front electronics panel of the Aixun T3A soldering station.  

On the AiXun T3A, the front GX12-5 aviation connector, does not have ESD protection circuit to prevent damage to the micro-controller.  Damage could occur from a static discharge when changing handles or inserting or removing solder cartridges. 

This PCB circuit and 3D printed case solve that issue.  

The circuit schematic was designed by EEVBlog forum user AL777.  I converted it to a PCB and designed a 3D printed case for it.  

Case was created with one GX12-5 connector on iron side, and a pigtail for base station connection side.   This was done to prevent connecting the protection circuit backwards.

Using two female panel mount GX12-5 aviation sockets are not recommended for this reason.  Do so at your own risk.

This mod is not difficult, but it requires proper electronics knowledge and both through-hole and SMD soldering skills.

NOTE:  Instructions are intended as guidelines and not meant for hand-holding users.

It is expected for users to have base knowledge and skills / knowledge for assembly.  

PCB components are through-hole with exception of three TVS diodes that require SMD soldering.  This can be soldered using hot air or precision tipped soldering tip and magnifying glasses.

If you have questions about this mod, design, or issues, I will try to answer them.

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IMPORTANT DISCLAIMER:   

THIS MOD IS FOR EXPERIENCED USERS WHO HAVE PROPER KNOWLEDGE AND TRAINING WITH ELECTRONICS SAFETY AND WIRING PRACTICES.  

USE OF THIS MOD IS DONE AT YOUR OWN RISK.  IMPROPER ASSEMBLY OR USAGE MAY RESULT IN FIRE OR CATASTROPHIC DAMAGE TO PERSON OR PROPERTY.  I TAKE NO RESPONSIBILITY FOR A USERS ACTION.

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Whats Included: 

• Case 3D print file .stl original 
• Case model in .STEP / .STP format. 
• PCB Gerber files
• PCB schematic
• Wiring diagram for GX12-5 connectors 

Required Components

For Case Assembly

• 8x M3 Heat-Set Inserts (amazon / aliexpress)
• 8x M3 x 6mm button cap screws
   

For Electronics Assembly

• 18 AWG wire. 
  -For the “IRON” side of pcb going to the GX12-5 to the Heater and GND holes.
  -For wiring of pigtail cable
   
• 24-20 AWG wire.   
  For the “IRON” side of pcb labeled ID, T, and T lines on PCB to GX12-5 female connector.
   
• 3:1 Heatshrink for 24 awg wire
• 3:1 Heatshrink for 18 awg wire
• 3:1 Heatshrink for cable pigtail from T3A front panel to ESD pcb.
• 1 Cable tie for pigtail
• 1x Male/Female GX12-5 aviation connector.   
   

For Electronics PCB Components  (See electronics schematic)

• 2x    100ohm Resistor
  1/4W  5% Tolerance - Axial
   
• 1x     10K Resistor
  1/4W  5% tolerance - Axial
   
• 3x    1uf Ceramic Capacitor
  50V Radial  0.100" lead spacing
   
• 3x    STS321033U202 TVS Diode
  in SOD323 package
   
• 1x     1N4148  Zener Diode
  100V,  200mA in D035 package
   
• 1x     2.65v @ 2mA LED color of your choice

How to make PCB

PCB can be ordered from a PCB fabrication house of your choice.  
JLPCB, PCBWAY, OSHPARK are just a few options available to you.

Upload the gerber .zip file to your pcb fabrication house of your choice and it should be plug and play.  That said, I have only uploaded to JLPCB.  Their defaults were fine.

Example cost from JLPCB is around $2-3 (not incuding shipping) for 5x boards.  Other vendors will vary.
 

Case Assembly

1. Case should be cleaned, deburred and checked for fitment.
2. File / sand any nibs or ill-fitting parts for best fitment.
3. Once a good fit is obtained, heat-press each of the four 3mm inserts into the corners of the top and bottom shell pieces.
4. PCB is press-fit into the case's pcb recess. 
5. Female GX12-5 socket attaches to side of case labeled “IRON”. 
6. Male plug attaches to end of pigtail connector, which plugs into T3A base station.
    

Electronics Assembly Wire Gauge

IMPORTANT:   T3A station can output 200W of power.  At 24VDC this is a theoretical maximum of ~9 amps.  Ensure your wire gauge can handle the maximum amperage.  

T3A uses short pulses of current to drive the heater.  Usually the station wont pull anywhere near 200W.  In typical use of a T245 or T12 cartridge, max amperage should be less than the stated 9 amp value, but different handles, cartridges, and use case will change this.   For example, 936 style handle requires longer pulses (duty cycle) at 100% power output in order to maintain heat.

18AWG wire should be more than suitable for wiring application.  20awg may also be suitable but use your own best judgement and research.

Assembly tips / suggestions:

1. Wiring Diagram:  Connector and pigtail should be wired according to the GX12-5 connector diagram attached.
    
2. GX12 connection:  Double check all connections before connecting to T3A host station and handle.  Use the attached GX12 connection diagram to ensure your GX12 connectors are properly soldered to your pigtails and pcb.
    
3. Pigtail Wiring:  
   
   The GX12-5 connector's strain relief accepts a maximum diameter cable of 5.9mm.  Its a very tight squeeze at this size.   
   
   Ideally, a 5 core 20-18 AWG silicone wire cable is preferred for the pigtail to T3A base station; but the GX12-5 connector diameter, its not possible.
   
   Suggestion option:  I suggest making your own cable for the pigtail.  This cable should consist (at minimum) of:
   
   
   1. Two (2x) 18 AWG silicone wire and from the BASE side of the PCB and the T3A GX12 connector.   
       
   2. Three (3x) 22-24 AWG silicone wires from the BASE side of the pcb to the T3A GX12 connector.  These wires are for the ID, S, and T connections.
       
   3. Then, a good quality silicone heat shrink over your pigtail wires to make a cable “sheath”.  
       
   4. Finally add a small piece of double insulated heat shrink to act as a strain relief where the cable interfaces with the GX12 connector.   The double wall strain relief usually consists of 1 wall of heatshrink and a layer of hotmelt glue which adds rigidity and weatherproofing.  
      
      I suggest test-fitting on scrap cable before trying this with the final pigtail.
       
   5. Your other options are to find a PVC or other coated wire material that will fit the connector.  
      
      Always test with scrap piece of cable and heatshrink strain relief to find the right combination that works for the GX12 connector.

Printing details:

• Model has only been printed using CURA slicer.
• Tested with PLA at 0.2mm layer height FDM print.   
• Cases should be printed face-down with the large flat top and bottom surfaces touching the build plate.  
• Supports are not required, however the cases text and ESD logo can be printed with better clarity using support with support interface enabled 
• For the adventurous you can fill the logo and text with paint of your choice using a precision tip dispensing bottle.