Tacho Repair
Posted: Fri Jan 19, 2018 6:35 am
Well my speeod has been playing up since I got the car. Feels like it reads reasonably well when cold, but as soon as the car warms up it feels like it reads nearly double what it's doing! I decided to give it a go of repairing myself. It's a early +2 but converted to negative earth with a Smiths RVI 2402/04 tacho.
I found this excellent write up http://www.sunbeamalpine.org/downloads/alpine_tach_repair_rev5.pdf showing what to do. I pulled my tach apart and it looked reasonably clean but some of the components looked a bit unhappy - especially the thermistor which had split it's casing. I do note that there is for a different part number tacho - but the internals look identical. We shall see!
I went to order all of the parts from Digi-key as the author had them all listed, but several were now out of stock or no longer available. I went through and found suitable replacements, the only one I couldn't find a like for like for was the thermistor.
The thermistor recommended was a Panasonic 300ohm item with a beta factor of 3900 in conjunction with a 34ohm resistor. The closest I could find from Digi-Key was a Amphenol 300ohm item with a beta factor of 3468. I threw together a quick spreadsheet to see how far out it would be. It was pretty close and needed a 37ohm resistor to bring it back.
This shows the difference in resistance vs temperature with the inline corrector resistors for both thermistors.
Here's the updated component list from Digi-Key with available items. All together they cost less than AUD$5 + post. The green ones are the items still available from the original article.
I'm still out at work, but I hope the little box from the States will be in my hot little hands when I fly home next week. I'll put up another update when I've actually done some real work.
PS, I'm a mechanical bloke - so no guarantees that I'm doing the right thing
I found this excellent write up http://www.sunbeamalpine.org/downloads/alpine_tach_repair_rev5.pdf showing what to do. I pulled my tach apart and it looked reasonably clean but some of the components looked a bit unhappy - especially the thermistor which had split it's casing. I do note that there is for a different part number tacho - but the internals look identical. We shall see!
I went to order all of the parts from Digi-key as the author had them all listed, but several were now out of stock or no longer available. I went through and found suitable replacements, the only one I couldn't find a like for like for was the thermistor.
The thermistor recommended was a Panasonic 300ohm item with a beta factor of 3900 in conjunction with a 34ohm resistor. The closest I could find from Digi-Key was a Amphenol 300ohm item with a beta factor of 3468. I threw together a quick spreadsheet to see how far out it would be. It was pretty close and needed a 37ohm resistor to bring it back.
This shows the difference in resistance vs temperature with the inline corrector resistors for both thermistors.
Here's the updated component list from Digi-Key with available items. All together they cost less than AUD$5 + post. The green ones are the items still available from the original article.
I'm still out at work, but I hope the little box from the States will be in my hot little hands when I fly home next week. I'll put up another update when I've actually done some real work.
PS, I'm a mechanical bloke - so no guarantees that I'm doing the right thing