TCI box - a successful repair
My '81 xs650 had been sputtering or more often just shutting itself off for no apparent reason - annoying in the middle of a sharp turn or pulling out into traffic. After checking various blind alleys I happened to notice that when I flipped the kill switch to "run" the neutral light would sometimes dim, which seemed strange. A glance at the circuit diagram shows the switch runs from +12 to the ignitor box. I hooked up my spare ignitor box and saw that the neutral light stayed bright. I left it hooked up and that fixed the problem with the bike.
I didn't see any obvious problems inside the ignitor box, but I recognized four white egg-shaped diodes, D1-D4, as being similar to one that had failed shorted inside a relay causing my neutral light to come on when the clutch lever switch was activated. I believe those diodes are fragile. In the ignitor box I scraped off some clear conformal coating from the diode pads and tested the diodes and discovered a couple had low resistance in both directions. They're easy to test in-circuit since they just run out to the cable.
I replaced the four diodes with 1N4005 diodes from Radio Shack. Since putting this box back on the bike it hasn't shown any problems. Before the fix the bike would have shut itself off a dozen times in this amount of time. If you make this repair, the marked end of the diodes should face to the left, and make sure they are solidly against the board when you solder them in, for strength against vibration. A dab of flexible glue under them wouldn't hurt.
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UPDATE 11 Dec 2010
A few days after writing the above, I had another, similar, stalling episode. At that point I removed the box again and examined all the solder joints on the board carefully. I saw several bad ones, a kind of degradation I hadn't seen before, caused by vibration I presume. See the third picture. The picture is an extreme case; look for just a faint ring as well.
Soooo, I used acetone and a toothbrush to remove the coating from the solder side of the board. I let it dry for awhile near a heat source. I then proceeded to re-solder every single joint on the board, adding a little solder to each joint. The purpose was to fix bad joints as well any joint on its way to becoming bad. I then used a toothbrush and denatured alcohol to remove the melted rosin solder flux left behind. I reinstalled the box, and as of now, 3 mos of daily riding later, haven't had a failure of any kind with it. The solder side of the board is still uncoated. I may put a coating on it if I stumble across one I like.
My '81 xs650 had been sputtering or more often just shutting itself off for no apparent reason - annoying in the middle of a sharp turn or pulling out into traffic. After checking various blind alleys I happened to notice that when I flipped the kill switch to "run" the neutral light would sometimes dim, which seemed strange. A glance at the circuit diagram shows the switch runs from +12 to the ignitor box. I hooked up my spare ignitor box and saw that the neutral light stayed bright. I left it hooked up and that fixed the problem with the bike.
I didn't see any obvious problems inside the ignitor box, but I recognized four white egg-shaped diodes, D1-D4, as being similar to one that had failed shorted inside a relay causing my neutral light to come on when the clutch lever switch was activated. I believe those diodes are fragile. In the ignitor box I scraped off some clear conformal coating from the diode pads and tested the diodes and discovered a couple had low resistance in both directions. They're easy to test in-circuit since they just run out to the cable.
I replaced the four diodes with 1N4005 diodes from Radio Shack. Since putting this box back on the bike it hasn't shown any problems. Before the fix the bike would have shut itself off a dozen times in this amount of time. If you make this repair, the marked end of the diodes should face to the left, and make sure they are solidly against the board when you solder them in, for strength against vibration. A dab of flexible glue under them wouldn't hurt.
~~~~~~~~~~~~~~~~~~~~~~
UPDATE 11 Dec 2010
A few days after writing the above, I had another, similar, stalling episode. At that point I removed the box again and examined all the solder joints on the board carefully. I saw several bad ones, a kind of degradation I hadn't seen before, caused by vibration I presume. See the third picture. The picture is an extreme case; look for just a faint ring as well.
Soooo, I used acetone and a toothbrush to remove the coating from the solder side of the board. I let it dry for awhile near a heat source. I then proceeded to re-solder every single joint on the board, adding a little solder to each joint. The purpose was to fix bad joints as well any joint on its way to becoming bad. I then used a toothbrush and denatured alcohol to remove the melted rosin solder flux left behind. I reinstalled the box, and as of now, 3 mos of daily riding later, haven't had a failure of any kind with it. The solder side of the board is still uncoated. I may put a coating on it if I stumble across one I like.
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