Author Topic: Best method for replacing PLCC SMT Sockets?  (Read 316 times)

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Offline micbr

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Best method for replacing PLCC SMT Sockets?
« on: October 19, 2019, 05:53:25 pm »

New member here, but frequent viewer of the EEVblog channel with a basic background in electronics repair. I'm doing some research ahead of a repair I need to attempt soon.

As a free-time project, I'm restoring a 1995 Digital Celebris 5100 PC (Pentium 90, Windows 95, etc). It's a complete back to metal restoration, rust removal, electroplating, the works. The machine is functional, but one of the surface-mount PLCC chip sockets for the Video RAM expansion has disintegrated. It was already broken when I acquired the machine, the plastic base was missing, and one end separated entirely when pressing a VRAM chip into place.

I've attached some photos of the socket below in the highest detail and resolution I could take.

Thankfully the pins and solder pads are intact - resting the chip loosely on the contacts does allow the RAM expansion to function, so that's a promising sign.

Removing the remaining piece of the socket shouldn't be difficult. However removing the sockets from the donor card and installing them onto the board presents a different problem. The pins are soldered inside the socket through cutouts in the plastic base, which means the pins can't be soldered individually or via drag soldering. So I'm guessing this would be more suited to hot air soldering.

Both the donor and target boards predate the introduction of RoHS, so the boards may use a lower temperature leaded solder (I'll make sure to check this first) which should hopefully make the repair easier.

What I'm looking to find out is -

  • Would hot air be an appropriate approach to remove and replace this socket, provided the temperature is kept above the melting point of the solder and below the melting point of the plastic?
  • Would it be advised to mask surrounding components, including SMT resistors, capacitors, adjacent RAM chips and through-hole tantalum capacitors?
  • What considerations should I take into account to avoid incurring further damage to the board? I know it sounds like an incredibly basic question, but I'd imagine one such consideration would be keeping the heat within a specific window to ensure the solder flows, but also to avoid lifting the traces.

I'm more than aware that for someone inexperienced with hot air rework, and on a difficult to source board, that this may be a job best left to someone with considerably more experience. That's something I'm perfectly fine with, however I still need to find someone reputable in Adelaide that could perform the repair.

A second option could be to remove the remaining piece of the socket and not use the VRAM expansion at all, but it feels like a job half-done and isn't ideal.

I'd rather ask questions first, check whether it's within my scope of knowledge and ability, practice on some scrap boards, then decide whether to proceed or enlist some outside help. The alternative is permanently damaging an out-of-production, difficult to source and expensive board. It's a "measure twice, cut once" type situation.

« Last Edit: October 19, 2019, 06:10:52 pm by micbr »

Offline The Senate

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Re: Best method for replacing PLCC SMT Sockets?
« Reply #1 on: October 19, 2019, 11:59:14 pm »
You could try gluing the two broken pieces together, then re-attaching it to the rest of the  socket. As long as you don't remove the IC too much it should be fine.
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Online Shock

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Re: Best method for replacing PLCC SMT Sockets?
« Reply #2 on: October 22, 2019, 02:06:09 pm »
I'd try removing those replacement sockets from heating the rear if there is nothing big on the other side. If you can get them past melt temp it should have minimal effect.

If you can carefully cut out the plastic bottom of the PLCC socket it can be soldered in with a fine soldering iron tip. Make sure the pads are perfectly flat and tack opposing corners into place. Add some insulative material back to the bottom when done if you need the IC raised.
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