[Informational] Reflow Repair of a Palm TX

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notipa
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Joined: Wed Jun 24, 2015 11:18 pm

[Informational] Reflow Repair of a Palm TX

Post by notipa » Wed Sep 09, 2015 6:59 pm

A friend of mine gave me a Palm TX with two critical hardware failures: half of the LCD is not functional, and the unit would lock up if flexed. The symptoms are typical of a unit that was bent, even though the largely plastic construction would hide many telltale signs of flexure. I suspect the LCD failure is a result of a cracked LCD display driver, which is not directly repairable; the LCD unit must be replaced. I had an existing TX whose components are known to work, and after testing with a new LCD I discovered the lock-up issue was not resolved. The failure mode was reminiscent of the Nvidia BGA failure of Dell laptops, which results from thermal expansion of the graphics chip causing the solder balls to crack. With little to lose, I did the same Nvidia reflow repair process to the numerous closely spaced BGA chips on the front side of the TX's mainboard, and found the process corrected the issue. Since the TX is different from a laptop motherboard, I have provided some instructions here.
  1. Remove the stylus, any accessories, and the four Torx T5 screws from the back of the unit.
  2. With a plastic spudger starting from the top left of the unit, separate the rear housing from the front housing at the cover/accessory slot. Be careful to not break the housing around the Athena connector area.
  3. The battery is soldered to the mainboard and glued to the rear housing. Either pull it off of the back housing (the glue can be quite strong, so exercise some restraint in your removal process), or desolder it from the mainboard. Generally, it's a rather bad idea to leave the battery attached while doing this.
  4. The LCD and Athena connector are held in place by two ribbon cables. Pop these off vertically with a spudger.
  5. Push on the LCD to lift the LCD and mainboard out of the front housing.
  6. With the plastic spudger, separate the LCD from the mainboard. There is a fair bit of weak glue holding the mainboard in place.
  7. Remove the foam pad and the four small foam blocks, exposing the ICs. Keep these away from dirt and grime as you reflow the mainboard.
  8. Cover the mainboard in aluminum foil, and cut out a hole or two to expose the ICs. If the battery is still attached, use extra caution to prevent shorting, and preventing the battery from heating past 60°C. You really shouldn't be doing this with the battery attached anyways.
  9. Reflow the mainboard. I used a heat gun at a distance of about two inches for thirty seconds. Don't burn the PCB or the components on it.
  10. After the PCB cools down, reattach the foam components. It is important that you do so, as the alignment of the On-button depends on the foam being present.
  11. You can reattach the battery as soon as now, or you can solder it back in place just before you close the housing. It is easier to do it now.
  12. Place the LCD in the housing (you can clean it just before this step, to clean those hard-to-reach corners effectively), then put the mainboard back in place. There are some brass pegs on the top of the front housing, to which the mainboard will align.
  13. Reattach the two ribbon cables.
  14. Poke around the unit to ensure the repair was successful before closing it up.
  15. Snap the rear housing back in place, securing the battery to the rear housing if you removed it. Make sure the battery wires do not press against the LCD or any connectors; you can check the LCD by turning the unit on and watching for LCD pressuring as you squeeze the housing together.
  16. Replace the four screws, stylus, and any accessories.

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