Sunday, February 12, 2012

Propeller crash

Yesterday I had another of those days that nearly made me decide to hang up my soldering iron for good. Some readers may have spotted the despondent blog post I made before I deleted it.

I assembled the Propeller LCD UI module. It went together easily and I had no trouble with the soldering using a magnifying lens (a strong pair of clip-on reading glasses clipped on to my normal reading spectacles) and resting my soldering hand on the desk to stop the shakes. But Murphy was not going to let me get off that easily.

Preparing to test the UI board I realized that I had skipped a page of the instructions and had not soldered a connector to the LCD daughter board. I thought that a connector for the main board  (a male 8 x 2 box header) had been omitted from the kit so I had installed one of my own. When I picked up the daughter board I saw the two rows of 8 holes and without thinking installed the 8 x 2 plain header that came with the kit. Also male. When I realized my mistake bad words were said. In all my years of kit building I have never before done anything quite so stupid.

I recalled Don Wilhelm W3FPR's advice to K2 builders who install multi-pin connectors on the wrong side of the board to sacrifice the connector and not try to remove it intact. This I eventually did with Olga's help. She suggested I place the soldering iron body along the row of soldered joints to melt all of them so the connector would fall out. That didn't work, but it did soften the plastic part of the connector allowing it to be pulled away. I could then remove each pin one at a time and clean up the through holes using one of Olga's sewing needles. Finally I was able to install the four 1 x 4 female headers that had presumably been supplied with the kit as a replacement for an 8 x 2 female that was really needed.

After all that stress (both to me and the board) I was relieved that when I plugged it in to the Propeller board and ran the demo program the UI module worked. But my happiness was short-lived. After I tried some modifications to the program I found that it seeemed to be crashing. The program would start at switch-on but would eventually hand up and not respond to the buttons. Sometimes garbage appeared on the LCD. The time before this happened got shorter with each attempt until sometimes the Propeller wouldn't even respond to the reset button. I restored the original program in case my changes were to blame, but the device was still crashing.

Next I re-heated all the solder joints I had made, though they all looked OK. On reassembly the Propeller still crashed. Thoroughly despondent by this point I typed a post describing what happened in the hope that someone would offer to come to my rescue (thanks to those who did.)

After a rest it occurred to me that I had crashed the Propeller by dropping the board a centimetre or so on to the desk. There was probably still a bad connection somewhere. I re-soldered all the joints, including all the ones on the main Propeller board. That had been ready assembled. I guess that the manufacturer had used lead-free solder because I couldn't melt the joints until I applied a bit of my own leaded solder to each one. Then all the joints looked nice and shiny.

After that treatment everything worked and up until now, cross fingers and touch wood, has continued to do so. So it seems that a poor soldered joint in the manufactured board was the cause of my problem! Thank you, Murphy, but I don't need your help. We do this for fun, do we?
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