TS450: Life after lightning

In August 2010, one of the Mid-Atlantic summer lightning storms did some damage — the strike was nearby and not direct, but it fried my Astron power supply, a Panasonic tough book, and my Kenwood TS-450SAT radio. The radio would power up and the display looked normal, but I had no audio and suspected that the front end and perhaps switching diode had been zapped.  At the time, I didn’t feel up to tackling the radio repairs, so based on eham reviews, I contacted KI4NR at LPC Wireless and mailed the rig off to Florida.

Meanwhile, I checked out the Astron and concluded that the voltage regulator IC was dead. After replacing the chip, the supply was as good as new.  Next, the computer: it had been interfaced to the radio via a G4ZLP cable, a work-alike to the original IF232 from Kenwood. As mentioned previously, I had modified the cable to also serve for CW keying of the rig. The computer powered up from battery okay, but did not work on wall power. A small board with the voltage regulator and battery charging circuits had been fried. I found the same model Toughbook on Ebay for a good price — broken screen, no hard drive or battery, and was able to combine the two into a functional unit.

LPC had sent me pictures of both the damage and repair, which are displayed in this posting.  When received by LPC, the lightning protection diode had vaporized and the PC board was charred. They repaired the lightning damage, but also performed factory calibration, enabled transmission on the 60m band, and replaced the backup battery, which was close to the end of its life.

The only item that didn’t work right was CAT control of the rig, but at first it wasn’t clear where the problem was: in the computer port, the interface cable or the rig itself. Swapping computers didn’t seem to matter, so the next step was to order another G4ZLP cable. Even with a pristine new cable, I was not able to establish serial communications to the rig.

Not having CAT control was a minor inconvenience. For normal operation, it wasn’t a big deal to type in the frequency, but for contests, it slowed me down a bit to not have the band map automatically populated. Similarly, for digital modes, it made operating awkward.

Looking at the schematic for the digital board within the TS450/690 service manual, there is an inverting buffer right after the physical connector to the cat cable. This chip is all there is between the outside world and the microprocessor that runs the radio. I reasoned that if the microprocessor had been cooked, nothing would work, so it was very likely that the 7404 chip had been cooked by the electrostatic discharge.  The chip is designated SN74AS04NS, so an “advanced schottky” version of the chip.

I couldn’t find that exact version of the chip, so I ordered the “next best” version: SN74ASO4D.  According to the data sheet, the two are electrically equivalent and have the same pin out. Both have 0.05″ pin spacing, but the dimensions of the ICs are slightly different: the D model is 1.75 mm shorter, 1.6mm narrower, and from side to side the “arm span” of pins is about 2mm less. I was hoping, though, that this would be close enough.

I removed the old 7404 by cutting the pins near to the chip body and then removed the remaining leads with a soldering iron. This left behind some clean, well-tinned pads. When I aligned the new chip, it was apparent that the replacement chip was not wide enough to span from pans on one side to the other. Since the new chip had the same pin spacing, I taped it in place and soldered one side of the chip, leaving a gap of 1-2 mm to the free pads.

After experimenting for a while, I settled on using a very fine tipped soldering iron and  made the connections using individual strands from stranded copper hookup wire. I did my best to check continuity, closed the radio up, and connected the newer interface from G4ZLP. I fired up Ham Radio Deluxe and defined a new radio, with communications set to the correct COM port, and serial parameters of 8 data bits, no parity and 2 stop bits. The radio synched up immediately and displayed the correct frequency. After brief testing, it appears that the CAT control is operating correctly.

I then went back and tested the original CAT cable from G4ZLP, and it appears that it had also died in the electrostatic discharge. Opening up the serial cable end connector, there is a small circuit board, covered by white rubber or silicone. I peeled a bit of it back to reveal a small circuit board with surface mount components. I didn’t consider it worth fixing, since I do have another cable that works fine.

Although it was something of a pain to replace the cable and the 7404 chip in the radio, the sacrifice of these two components was far preferable to having the damage go one chip further and take out the radio’s microprocessor.