I read somewhere that the old ones needed a retrofit, ,as I recalled they needed a shroud over the eye, I saw something somewhere describing it,,
This was/is the Fromeco model. David had one, and it was very inconsistent. It had the detector behind a window. I theorized that it was getting multiple reflections, so David cut a hole in the window, and added a short ~1/2" diameter baffle around it, so the detector was exposed and couldn't get reflections from the side. It worked good then. We relayed these observations to the people who make it and they changed it - *to have the detector at the bottom of a long, skinny, highly reflective* tube, about 3/16" in diameter and about 4" long. This was silly on two scores - first, the last thing you want is to put it at the bottom of a shiny tube, which guarantees you get lots of reflections, and second, the fact that the sensor is now buried deep inside the box, it's very difficult to move it to the front of the box, where it should be. It seems to work OK if you get it the right distance, but is nowhere near as consistent at getting readings, particularly at a long distance, as the original TNC or Skyborne.
The original TNC and Skyborne tachs had it right as far as the design goes. The weak point, to which Howard refers, is in the mechanics of the enclosure, switches, and display. The most common issue is that the display works its way out of the socket after too many drops and tosses across the circle. The symptom is that some or all of the letters fail to display, or the display is inconsistent. The solution is to push it back into the socket. To keep it from happening again you can make a spacer out of plywood and weatherstripping attached to the case that keeps it pushed into place.
Another common issue is that it fails to turn on, or it fails to switch from 2 blade to 3 blade. This is because the switches are soldered directly to pins sticking up from the circuit board. This puts all the load of moving the switch on the pins. Eventually, one or more of the solder joints breaks and the switch is ineffective. Quick fix is to solder it back. A longer-term fix would be to mount the switches directly to the case with screws, and then use flexible wire or a ribbon cable (with a lot of slack) to connect it electrically. Howard told me that the switches are failure prone, but I haven't seen a switch failure, just switch attachment breaking the solder joint. They get dirty so when I replace the battery every 5 years, I squirt some contact cleaner it there.
The last very common problem is that the plastic screw head pockets on the battery end of the bottom plate cracks from screw pressure. You can glue it back a few times, but eventually everybody ends up using longer screws with big washers on the outside. The same thing does not tend to happen at the sensor end, because the the thing that breaks off on the bottom is clamped solid to the circuit board.
I had one of the Skyborn versions that apparently used RoHS lead-free solder, and had a tin whisker that made it not work. I cleaned it up and no problems for the last 10 years or so. That's the only example of that I have found.
Oh, yeah, as everyone has found the plastic case is easily melted with Lacquer thinner or acetone, so all of the ones around here have ugly melted spots or bits of paper towel glued to the outside.
This all sounds like a lot of problems but it should be noted that I am using my very first tach that was acquired very early on from Tony directly, and it's about 20 years old and works as well as the day I got it. I think Ted is still using his, as well. I also have two Skyborn units that are essentially the same thing and also worked perfectly the last time I needed it. The biggest on-going issue I have had is not with the tach but with the battery failing or blowing up from the high temperatures you get in the back of a black van that sits out in the Sun for 12 hours.
If this is one of the originals or Skyborn types, I would be willing to be it can be made to work by checking the known trouble points.
Brett
p.s. btw, the battery lasts forever if it *doesn't* explode. I had a switch connection fail and after fiddling around with it as the field, I ended up taking some copper line-wrapping wire and shorted it across it by wrapping around it. I forgot about it, left it that way, put it in the box, and went home. About 3 weeks later I went to start my engine and sure enough it was still on, and worked fine.
Topic: Tach (Read 4264 times)