Electronics > Repair
removal of 7-segment displays from PTH board
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BurningTantalum:
I have a pcb with 8 x 7-segment displays, two colour, single digit, located tight together in a row, with 5 pins on the top edge and 5 on the bottom edge. They have all got failed segments probably due to being overdriven to achieve the brightness to be visible through the tinted glass panel they sit against. I am a bit wary of trying to remove them and wonder if anyone has any tips and suggestions. I have a Pace MBT with desoldering wand, and a hot air gun (that wanders a lot in temperature) and am fairly experienced with desoldering small components. The pads on the solder side are really small so I worry about damaging them and/or pulling out the through-hole plating due to so many pins.
Regards, BT
jpanhalt:
There are several possibilities.  If the leads are accessible, cut them, then remove the pieces from the board. They can be cut either with snips or a small burr in a Dremel like tool.   Hot air is another possibility.  Low-melting solder is another.  I usually go the cut and remove approach, if not surface mount or I don't need to preserve the piece being removed.
tooki:

--- Quote from: BurningTantalum on August 09, 2024, 10:20:34 am ---…
 The pads on the solder side are really small so I worry about damaging them and/or pulling out the through-hole plating due to so many pins.

--- End quote ---
Am I understanding correctly that your only concern is damaging pads/PTHs?

I assume by “desoldering wand” you mean a vacuum desoldering handpiece? I assume it is continuous-vacuum (i.e. vacuum continues as long as you hold the trigger, as opposed to a solder sucker where you get one finite “shot” of vacuum)?

If so, then you just need to learn proper desoldering technique. With proper technique, you won’t damage the PCB. When done properly, components should practically fall out of the holes.

I’ve found no better tutorial on this than this video manual from Pace. It’s technically for one of their old handpieces, but just skip the parts that are tool-specific and look at the technique shown, because it works with any continuous-vacuum desoldering system.

Haenk:
A picture would help.
If it's a dual layer board, touch up all the solder joints with fresh solder, better add some extra, that will ease extraction. If it's a private repair, use 60-40 solder. The desoldering should be fairly easy with fresh solder.
Use a good amount of heat for the desoldering iron, I run my pace at 460 oC most of the time. Need to be quick though. Don't use any pressure on the plating, only initially on the cold solder. The plating should not suffer (unless it's one of those awful Phenol-based single-sided hard paper boards)
tooki:
460°C? Yikes. What condition your desoldering tips are in, when run like that?

I have a Pace desoldering iron, too, and usually run it between 350-400°C. I just preheat the board with hot air if needed, and/or add auxiliary heat with a soldering iron.
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