IC Removal and Socketing

A BIOS upgrade kit for a Dell 310: a U-shaped chip puller with hooked tips, two 28-pin DIP chips and the plastic tube they came in.

IC removal and socketing covers taking a dual in-line (DIP) chip out of a board without damaging the chip or the board, and fitting a socket in its place so that the chip can be changed again without heat. On a vintage machine it is how a suspect chip is swapped for a known-good one, how a failed chip is replaced, and how an upgrade such as a replacement ROM is fitted. Ray Carlsen's advice after any chip has been desoldered is to fit a good-quality socket, so that the area never has to be heated again; each round of heating degrades the board.

A chip that is already in a socket comes out with an extractor or a small screwdriver. A chip that is soldered in has to be desoldered first, or cut out if it is cheap and already proved faulty. Those two jobs are described in full in Through-Hole Desoldering; the steps below are the ones specific to chips and sockets.

When to use it

• A chip is suspected and the machine has no spare of it, or the chip is soldered in and has to be tested by substitution. Carlsen's view is that substitution is the only practical way to check most chips in a machine like the Commodore 64.
• A chip has been proved faulty and needs replacing.
• A socket is itself suspect. Old sockets corrode and lose their grip; on Commodore 64 boards Retro Repairs and Refurbs found one fault caused by a loose, corroded PLA socket.
• An upgrade or replacement part needs to plug in, as with ROM replacements and modern adapter boards.

Before removing anything, look for faults that do not need the chip out: a supply out of tolerance, a missing clock or a short on a line; see Logic Chip Testing and Continuity Testing and Signal Tracing.

Safety

• MOS and CMOS chips can be damaged by static. Carlsen warns that the Commodore chips are static-sensitive, and NASA's soldering standard required static-sensitive parts to be stored and handled under electrostatic discharge controls. Use an earthed wrist strap with a series resistor; see Recommended Tools.
• Unplug the machine first. For the heat, fume and lead hazards of desoldering, see Through-Hole Desoldering.

Tools and materials

• An IC extractor, or a small flat-bladed screwdriver with a layer of tape round its tip to protect the board.
• Fine tweezers for straightening pins.
• Desoldering tools, for a chip that is soldered in; see Through-Hole Desoldering.
• A new socket of the right pin count and row spacing. DIP sockets come with rows 0.3 in (7.62 mm) or 0.6 in (15.24 mm) apart, and 28-pin sockets are made in both widths.
• Small flat-nosed pliers, for cleaning the pins of a chip that is to be reused.
• A soldering iron, solder and flux; see Through-Hole Soldering.

Socket types

Stamped-contact DIP sockets for 16-, 14- and 8-pin chips.

A 16-pin machined-pin (turned-pin) socket, with a round receptacle for each pin.

DIP socket contacts

Type	Construction	Notes from the sources
Dual-wipe (dual leaf)	A stamped spring contact that grips the flat chip lead	TE Connectivity makes its dual-leaf contacts from phosphor bronze, rates them at 20 mΩ maximum contact resistance and up to 300 g insertion force per contact, and designed them for machine insertion.
Machined pin (turned pin)	A spring clip with several fingers pressed into a machined round shell	Mill-Max uses a four-finger beryllium copper clip rated at 3 A, and its machined sockets accept round leads 0.38 to 0.64 mm (0.015 to 0.025 in) in diameter as well as standard IC leads. TE's four-finger contacts, machined or stamped, are rated at 10 mΩ maximum and need an average of 179 g (machined) or 134 g (stamped) to insert.

Machined sockets take round pins as well as flat IC leads, which matters for some modern replacement modules. Older boards may carry single-wipe sockets, as on the Commodore PET 4000 series. Device guides record which type suits particular chips, and where a socket is too tall for the case; see the worked examples below.

Procedure

Note the orientation

1. Before removing anything, note which way round the chip is fitted. A DIP chip marks its pin 1 end with a notch, a dot near pin 1, or both, and the pins are numbered anticlockwise from pin 1 when the chip is viewed from above.
2. Note the orientation of the socket as well, if it has a notch, and any marking for pin 1 on the board.

Remove a socketed chip

1. Fit the extractor's hooks under the ends of the chip, or work a taped screwdriver under one end.
2. Lift the chip a little at a time, prying alternately at the two ends.
3. Take care not to damage the circuit board while prying.
4. Check the pins of the chip that came out, and straighten any bent ones with tweezers.

Remove a soldered chip intact

Use this for a chip that may be good or is hard to replace. The full method is in Through-Hole Desoldering; the points that matter most for a chip are:

1. Clear every pin of solder, on both sides of a double-sided board.
2. Check that every pin is free by wiggling it with tweezers, and rock the chip from side to side until all the pins click loose.
3. Pry up one end gently, then the other. If any pin sticks, stop and free it.
4. Do not force the chip out even when every pin looks free; a little hot air once all the pins are clear of solder helps.

Remove a chip by cutting it out

Use this only for a cheap chip that has been proved faulty. Cut every leg, lift the body away, then remove the stubs one at a time and clear the holes; see Cutting out a part that is being scrapped.

Fit the socket

1. Inspect the board on both sides with a strong light and a magnifier. Repair any broken track or torn plating now, because it will be hidden under the socket.
2. Make sure every hole is clear of solder; hold the board up to a light to check.
3. Check the new socket's pin count and row spacing against the chip.
4. Put the socket in the board with its notch at the pin 1 end.
5. Fit the socket empty. Never solder a socket with a chip in it: solder on the chip's pins sticks to the socket contacts, and the chip may never come out again.
6. Hold the socket flat against the board and solder one pin. Check that the socket is straight and flat, and reheat that pin to adjust it if not; then solder the remaining pins.
7. Solder each pin carefully and inspect for bridges between pins; see Through-Hole Soldering.
8. Clean off the flux.
9. Check continuity from each socket contact to the track it should connect to, and check neighbouring contacts for shorts. See Continuity Testing and Signal Tracing.

Fit a chip into the socket

1. If the chip has been used before, clean its pins by squeezing each one gently with flat-nosed pliers. A blob of solder left on a pin can force the socket contacts too far apart and spoil that contact. Bend the pins as little as possible: they break if flexed too many times.
2. Check for bent pins and straighten them with tweezers.
3. Hold the chip over the socket with its notch towards the socket's notch, or the pin 1 marking on the board.
4. Line each pin up over its contact before pressing.
5. Press the chip in with firm finger pressure on its top until it is fully and evenly seated.
6. Check that no pin has folded under the chip or out to the side.

Testing with a socket fitted

A socket makes the most useful chip tests possible:

• Substitution: swap the suspect chip for a known-good one. Carlsen's quickest version is to put each suspect chip into a working machine that already has all its chips socketed.
• Piggybacking: for some faults a known-good chip pressed on top of a suspect one, pin to pin, changes the symptom and points to the faulty chip without any desoldering. The repairer iz8dwf found two partly failed DRAM chips in a Commodore 64 this way, and reports that it works about half the time; the pins must be clean, every pin must make contact, and no pin may touch its neighbour. Terry Stewart used it to confirm a faulty 74-series logic chip in an Apple IIe, and notes that it only works for some kinds of fault.
• Out-of-circuit testing: a socketed chip can be tested in a chip tester; see Logic Chip Testing.

Checking the repair

1. Check that the chip is the right way round, that every pin is in its contact, and that none is folded under.
2. Check continuity from each socket pin to its track, and for shorts between neighbouring pins.
3. Power up and test every function that depends on the chip.

Common mistakes

• Soldering a socket with the chip in it.
• Fitting the chip the wrong way round. SparkFun warns that a chip connected the wrong way may smoke, melt and be ruined.
• Levering against the board with a screwdriver.
• Pressing a chip in without checking each pin, so that one folds under.
• Refitting a chip with solder still on its pins, which spreads the socket contacts.
• Straightening the same pins again and again until they break. Carlsen's repair for a broken pin is to tack-solder a short wire to the stub left on the chip body and cut it in line with the other pins.
• Fitting a socket without inspecting the board first, so that a broken track or via is hidden under it. On one Commodore 64 board a non-factory PLA socket had damaged two vias underneath.

Worked examples on this wiki

• Commodore 64 PLA Replacement: removing a socketed or soldered PLA, fitting a 28-pin socket, and a case where a loose, corroded socket was the fault.
• Sinclair ZX Spectrum ULA Replacement: levering the ULA out evenly with a removal tool, sockets that accept only small pins, and the height of a socketed chip under the case.
• Sinclair ZX Spectrum RAM Replacement: dual-wipe or turned-pin sockets for the RAM, and replacement modules with round pins.
• Commodore PET 4000 Series RAM Replacement: turned-pin sockets in place of the original single-wipe type, and corroded sockets from earlier repairs.
• Commodore VIC-20 Blank Screen Repair: reseating every socketed chip, and a socket contact bent by an earlier chip.
• Sinclair QL RGB Port Repair: the socketed ZX8301, and Sinclair's advice to test a suspect chip by fitting it in a known-good QL, and not to put a good chip into the faulty machine.

Related pages

• Through-Hole Desoldering
• Through-Hole Soldering
• Logic Chip Testing
• Continuity Testing and Signal Tracing
• Via and Through-Hole Repair
• Recommended Tools