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Bench testing a tach
Posted by: Chris Lampe ()
Date: August 18, 2005 02:53PM

I just picked up an early spyder dash that I plan on installing in my '64 Monza. Before I install it I want to to test it out. I have successfully tested the fuel and temp guages on the bench but I can't seem to get the tach to work. What Am I missing? I hooked the tach to a signal generator and injected a 12v 3khz square wave but the tach does not respond, any suggestions on what else to try.

Chris
Rowlett, Tx
NTCA - North Texas Corvair Association
CORSA
'64 Monza 'vert

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Re: Bench testing a tach
Posted by: naderaggravater ()
Date: August 18, 2005 03:28PM

Chris,
Here's a link to early and late tach schematics.
[www.mindspring.com] Informational Resources)
I found the voltage regulator bad on mine.

Jerry

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Re: Bench testing a tach
Posted by: naderaggravater ()
Date: August 18, 2005 03:31PM

Looks like the link doesn't attach correctly.
It's found at Rads Informational Resources.


Jerry

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Re: Bench testing a tach
Posted by: SeaKing ()
Date: August 18, 2005 03:32PM

Typo in the url. This should work:

[www.mindspring.com]

Chris K
Corsa Ontario
Paintless '65 Monza 180/4
Former owner of a catastrophically rusted '65 Corsa 180 (Canuckmobile)

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Re: Bench testing a tach
Posted by: cepak ()
Date: August 18, 2005 03:45PM

I've got the wiring diagram for hooking up the tach. I'll send it to you as soon as I dig through my email and find it.

Oh, and I have a spare set of Spyder gauges. If something doesn't work and you figure out how to bench test the gauges, let me know.



Edited 1 time(s). Last edit at 08/18/2005 03:47PM by cepak.

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Re: Bench testing a tach
Posted by: Chet ()
Date: August 18, 2005 04:55PM

What's wrong with connecting the tach to the engine? All you need is a grounding wire, a wire connecting from tach to 12v source, and a wire connected to '-' side of coil. How hard is that? No fancy expensive equipment, no wiring diagrams.... just a simple hook-up.

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Re: Bench testing a tach
Posted by: acardon ()
Date: August 18, 2005 05:33PM

I think Chet has the right solution. Are you grounding the signal generator to the tach? Isn't 3k cycles per second too fast for a distributor running at 18k cycles per minute at 3000 RPM? Also, the tach circuit may reqire more current draw than the signal generator will provide.

The Trunk Belongs in Front, Ask Any Elephant
Caution: Images in This Mirror May be Waterpumpers
Don
NTCA....DFW,TEXAS
66 Monza 1 owner

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Re: Bench testing a tach
Posted by: VairKing ()
Date: August 18, 2005 08:02PM


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Re: Bench testing a tach Mission complete!!
Posted by: Chris Lampe ()
Date: August 19, 2005 12:00PM

After reviewing my math, I realized that I had a wrong calculation. It turns out that I should have been using a frequency of 150hz for 3k RPM and 300hz for 6k RPM. Now that I have that part figured out I still had a problem with the tach. The meter movement was missing the glass bearing that the meter is suspended on. After some careful inspection of the meter movement I found the glass bearing lying inside the coil of the meter movement. I reinstalled the glass bearing on the pivot shaft of the meter movement, reassembled the tach and tested it on the bench. It worked!! Yeeah haw!!! I then calibrated the tach. The other gauges were checked out as well and found to be in working order.


Thanks to Chris K and Jerry for posting the link to the tach schematic I was able to figure out the correct way to hook up the tach on the bench.


Chris
Rowlett, Tx
NTCA - North Texas Corvair Association
CORSA
'64 Monza 'vert

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Re: Bench testing a tach
Posted by: cepak ()
Date: August 19, 2005 02:38PM

How did you bench check the Head Temp gauge? Did you very the voltages?

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Re: Bench testing a tach
Posted by: Chris Lampe ()
Date: August 19, 2005 03:02PM

Tom,

Yes I just varied the voltage to the temp gauge.

On the link that Jerry and Chris K provided there is a page that has the temp vs resistance curve, I will use this data and retest the gauge later today and report back.

In order to test the guage with the temp curve data you will need a 12v source and a 1k pot or some fixed resistors.

200 deg ~= 1k ohm
300 deg ~= 500 ohm
400 deg ~= 300 ohm
500 deg ~= 150 ohm
600 deg ~= 80 ohm

Chris
Rowlett, Tx
NTCA - North Texas Corvair Association
CORSA
'64 Monza 'vert

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Re: Bench testing a Temp Gauge
Posted by: Anonymous User ()
Date: August 19, 2005 03:38PM

You do NOT vary voltage....should be 13.6-14.4 vdc!

You vary the resistance....




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Re: Bench testing a Temp Gauge
Posted by: Chris Lampe ()
Date: August 19, 2005 06:30PM

Matt,

You are correct, do not vary the volts. I just did this as a quick test to see if the gauge would wiggle. But as I also said to Tom I was going to get a 1K pot and test the gauge again. I have done this now and the gauge will move between 400 and 600 degrees, I'm not sure why I can not get it to go down to 200 dgrees. The gauge reads 400 degrees with nothing hooked to it.

Chris
Rowlett, Tx
NTCA - North Texas Corvair Association
CORSA
'64 Monza 'vert

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Re: Bench testing atemp gauge
Posted by: Anonymous User ()
Date: August 19, 2005 07:00PM

As you can see.. you'll need at least a 1.5k pot to drive it down....1 0k is just above 200

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Re: Bench testing atemp gauge
Posted by: Chris Lampe ()
Date: August 19, 2005 07:38PM

Matt,

I could not find a 1k pot the smallest I was able to find was a 5k but even if I had a 1 k pot I still should have been able to go below 400 degrees. The way I read the curve he has 2 sets of data points and at 200 degrees on one reading he read 800 ohms and on the other he read 1.3k ohms. I realize that I will not be able to get an exact reading on the bench using a pot, but I should be able to move the needle over the entire operating range if the gauge is working properly.

Chris
Rowlett, Tx
NTCA - North Texas Corvair Association
CORSA
'64 Monza 'vert

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Re: Bench testing a tach
Posted by: J.O. ()
Date: August 19, 2005 08:13PM

If you are planning on using the boost guage as a vacume guage, you cab clean of the the little rack and pinion with solvent the re-oil with some very light instrument oil. It will function better if cleaned.

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Re: Bench testing a tach
Posted by: Chris Lampe ()
Date: August 19, 2005 08:24PM

J.O.

Thanks for the tip on the boost gauge, I have not yet decieded if I'm going to use it or not but if I do I will clean it up following your tip. I see that VDO makes clock [www.nhspeedometer.com] that I think will fit in place of the boost gauge.

Chris
Rowlett, Tx
NTCA - North Texas Corvair Association
CORSA
'64 Monza 'vert

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Re: Bench testing a tach
Posted by: Anonymous User ()
Date: August 19, 2005 10:05PM

Gauges are 40 yrs old! Movements are stiff!

Same with distributors.....no way will any of them do what the book says.

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