Tach Problem

[Alpine James]

Hi all,

My latest and hopefully nearly last re-wiring issue is the tach on my S-V. I originally thought the induction coil loop fittings had gone missing and tried to fab a new one but with no success. As luck would have it, I found both the plastic holder and the metal clip. After checking the wiring many times over, both leads from #2 terminal on ign switch, one to spade on the tach, the other through the induction loop on the tach then to ballast resistor and + terminal on the coil, there is still no reading on the tach.

Am I missing something or is it a faulty tach?
Is there a relatively easy way to bench test?

Thanks, James

 

[Ken Ellis]

Here's a good thread with worthwhile contributions from Tom H.

http://www.sunbeamalpine.org/forum/showthread.php?t=24568

...in which he references this article:

http://www.sunbeamalpine.org/downloads/alpine_tach_repair_rev5.pdf

Sort of depends on how much test gear you have available. I do think an iPhone/Android signal generator app and a decent audio power amp could provide the necessary test signal, but it would be best to check that on a scope before using. Probably easier to generate it with the car instead.

I think Tom H has offered guidance on your tach issue in the past; he'll likely be along presently...

 

[Tom H]

James, It could be a failed tach, I have seen a few, but mostly these tachs lose calibration rather than fail outright.

I know you have rewired your Alpine and I suspect that a wiring error is more the cause. You describe the two wires involved- one to power the tach and one thru the induction loop. Correct. BUT is the wire thru the induction loop the only wire going to the coil? In order for the tach to respond to the current pluses of the coil, ALL power to the coil must go thru that induction loop. I suspect that before you reinstalled the tach and before you ran that wire thru the induction loop, you had the car running, clearly indicating you had installed a wire to power the coil. And now you have ADDED another wire to the coil thru the induction loop. So some of the power goes thru the wire you installed earlier and some goes thru the induction loop. NO GO! Gotta remove the other wire going to the coil. Quick test- remove the induction loop wire from the #2 terminal of the Ign switch and see if the car runs. It shouldn't. If it does, then there's the problem.

Other possibilities are that when you installed the steel clip you did not make sure the tips of the steel clip were making contact with the mating tips protruding out from inside the tach or that you looped the wire thru the plastic piece in the wrong direction- or are you using the original wire already looped thru the plastic.

Hope this helps, Tom

 

[Paul A]

As usual, excellent commentary by Tom H Also, be sure the loop is traveling in the right direction. see attachment A goes to 12v+ terminal on coil B goes to #2 terminal on ignition switch.

 

[jfcroni]

Agreed... it will not work the other way around with one loop as shown in the pic. The ends must leave the bracket as shown.... I just went through this too. - Jim

 

[Alpine James]

OK,

So to check off:

There is only the one wire from ign #2 power to induction loop to ballast resistor to + on coil. Negative on coil goes to distributor. Car starts fine.

The loop is as shown on the diagram, strictly by luck. Maybe I should have caught that but electrics/electronics was not my best class in tech school.

Checked the clip to ensure good contact inner and outer.

Still no movement on the tach.

Any chance it is a ground issue?

Thanks, James

 

[Tom H]

Surely could be a ground issue. Is the tach illumination lamp installed? Does it light up? If so you have a good ground.

I still want to verify the "one wire" to the coil. You say that there is just one wire from the #2 terminal to the induction loop and on to the coil. But is there not another wire to the ballast resistor and on to the coil- not coming directly from the #2 terminal. Or was that one wire now looping thru the tach the same wire powering the coil even before you installed the tach?

Tom

 

[Alpine James]

Only one wire with the resistor series. Ign #2 through tach loop to the ballast resistor and then from the resistor to the coil +.

 

[Tom H]

James,

And I assume you have verified the tach ground as I noted

And just to humor me, please confirm that the wire, from terminal #2 on the Ign sw, now looping thru the tach was the same wire powering the coil before you installed the tach. And confirm that if you disconnect that wire from #2 terminal the car will not run.

Trying to be 100% sure that the problem is not something simple that got lost in translation.

Tom

 

[Alpine James]

Got it sorted. Was the ground of course. Disconnected while playing the gauge wiring and not properly reattached and since not an issue with the fuel and temp gauges let it slip. Thanks for all your help. Doubt I would have ever figured out the induction loop direction on my own

Thanks, James

 

[Tom H]

Great news. Like I suspected, something simple.

 

[Jimjordan2]

Ain't it always the ground? Just made me chuckle a bit. So many of our Alpine problems are always the grounds.
Thought I was gonna be clever and humorous about this, but once I thought about it, there was nothing that humorous.
Glad you found the problem. Good Cruising.