Dead tachometer?

Howdy folks. Anyone ever have their tach drop on them? I recieved a dead tach from a fellow member as part of a trade and was inspired to take it apart. I was reading an open coil on the movement so I decided to focus on that assembly. I took the spindle cages apart (no small feat) and pulled the spindle/coil assembly out. Now, as most of you know, a meter movement won't work if the coil is burned out and this is what I thought I was facing. I peeped at the coil assembly under my microscope (eyes ain't what they used to be) and found the coil lead had burned off of the connecting terminal. I scraped the insulating varnish off of the wire with a small chisel backed up with a discoid (dental tools) and had enough slack to solder it back into place. Viola! It lives again! I'm amazed at how very complicated the assembly was and how easy it was to fix. I hope this post encourages others to try their hand at saving their assemblies. If not, please feel free to contact me and we'll see if we can't walk through the process together. I only wish I had a camera attached to my 'scope, I'd have taken pictures of the process.

 

Good deal Robert!
In my career I have repaired many a meter movement. Usually from a bad solder connection or broken wire as you found.
A good feeeling to repair what most people would trash.

My present tach is a mechanical type and when running ~4000 rpms it drifts all over from 3000 to 4500. So I am preparing to change my 81 xj650 over to an electronic type tach.
Pretty simple mod I think................
But you never know!

 

I had a fuel gauge on my boat fail. Similar problem.

Only took me most of a day to diagnose and correct the problem on a gauge I coulda replaced for $20

At least with an XJ tach it's worth the effort.

 

Hey greengoon, I just changed my mechanical tach on my '81 XJ650H to an electronic one. It was easy and it works great!

They physically mount the same to the instrument bracket. Electrically, all you have to do is add one wire from one of the coils up to the headlight bucket. The swtiched +12 volts and instrument light wiring is already in there.

Make sure you use the schematics so you get it right.

 

Git,
Thanks for the info.I don't think there is much to it!
George

 

Hello Robert, it's me again!

My tach does not work. The needle is broken, the needle rests when off at around the 1500 mark, and when on the needle jumps around almost as if it is due to the vibration of the engine, as it only moves a few hundred rpms in any direction.

Is it fixable? What are the steps to trouble shoot the tach in an effort to repair it.

Thank you!!

 

day7a1, you can use needles off of a Ford Escort or similar model (someone posted pics of this swap, look around) to replace your broken needles. I've got to do the same for mine shortly.
There are three contacts on the back of your tach. One is ground (Black) the other two are your coil leads. Brown is +12 vdc from the fuse panel and the Grey is the pickup from the TCI/ignition coils. You should be able to see a resistance across the Grey and Black and across the Brown and Black. I don't remember what I measured back then but you should be ok with readings from 2 to 150 ohms across the pairs. If you read infinitive resistance across either pair, you have an open coil and need to dig to see if it is repairable. Worst case, you can shoot me your # and I'll walk through the test with you