Thursday, January 4, 2018

Extreme IC repair

For Christmas, our family of hams got Cricket 80A transceiver kits.  They are not terribly hard to assemble and are good soldering practice. 

One problem we had with two of them was that the local oscillators did not start up.  It turned out that the 2N7000 MOSFETs are susceptible to electrostatic discharge (ESD) damage.  For whatever reason, the Q1 local oscillator transistor seems more vulnerable to this.

But in one of the kits, there was a problem with the audio amplifier IC, an NJM-2113D.  In the process of soldering and apparently removing, three pins broke off.  These are not exactly standard, at least they're not in my junk box. So although I put in an order for a replacement, Donna pointed out that I could probably fix it anyway.

The issue is that pin 1 (GND) broke off at the case, so I set about using a four fluted 1/8" endmill to cut the case to expose more of the pin.  I gripped the endmill in a collet in the headstock of my lathe.

My biggest concern was part-holding.  Fortunately, I was able to grip the IC in a toolpost, which also didn't break it.

After a few passes, I successfully exposed what seemed like enough of the pin to take solder.

I started by soldering the intact pins to the board and then the third pin, which was broken off, but not all the way at the case.  For this, I ran a piece of tinned copper wire through the hole, soldered it to the board, and then to the IC.

Then I ran another piece of tinned copper wire through the hole for pin 1 until it stopped on the exposed part of the IC, and soldered it to the board.

Finally, I soldered the new pin 1 to the IC.  I used a bit too much solder, but it's a good connection.

And, it works!  Here is the happy owner of the completed radio.

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