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05-17-2004, 05:19 PM
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Banned
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Join Date: Oct 2003
Location: Yorba Linda,
CA
Cobra Make, Engine: SPF w/392CI stroker
Posts: 3,293
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Not Ranked
Electrical 101 - I really suck at this....
Friends,
Here's my situation. I have a digital multi-meter and I want to test the output voltage coming from the "tach output" on an MSD 6AL. This is typically a single wire that goes from the MSD box to the tach signal wire (or to an MSD tach adapter). On an SPF, the tach signal wire is black/green.
My tach is dead and I want to test the MSD 6AL for output voltage. A reading of 1-5 volts is normal....a full 12 and the MSD box (tach output connector) is bad and needs to be fixed at the factory.
On this digital multimeter I'm a total novice on "what" and "how" to probe. I know enough to set the dial to 20V (20 volts or less), but I have no idea where to probe the black wire to complete the circuit.....ground????
I feel so stupid....
-Deano
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05-17-2004, 05:34 PM
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CC Member
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Join Date: Feb 2001
Location: BRADENTON,
FL
Cobra Make, Engine: KIRKHAM 427 S/C, SHELBY 427 ALUM. STROKER
Posts: 1,396
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Not Ranked
Black (-) to ground. I assume you came up with the voltages from
the mfrs instructions or trouble shooting guide. It should tell you
if your'e measuring AC or DC. Set your meter accordingly.
Good Luck, remember, Edison started somewhere !!!  |
05-17-2004, 05:39 PM
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Banned
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Join Date: Oct 2003
Location: Yorba Linda,
CA
Cobra Make, Engine: SPF w/392CI stroker
Posts: 3,293
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Not Ranked
Quote:
Originally posted by MOTORHEAD
Good Luck, remember, Edison started somewhere !!!
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Yeah, I even did my 5th grade book report on him. Look where it got me!  |
05-17-2004, 05:58 PM
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CC Member
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Join Date: Dec 2001
Location: San Diego,
CA
Cobra Make, Engine:
Posts: 2,979
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Black to ground. If it sparks it's wrong. 
Seriously. Set the multimeter <20 VDC. Put the red on the tach output and the black to ground.
__________________
Remember, It's never too early to start beefing up your obituary.
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05-17-2004, 06:50 PM
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CC Member
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Join Date: Oct 2003
Location: St Charles,
MO
Cobra Make, Engine: NAF 1970 SC 428CJ
Posts: 25
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Smoke is NO GOOD
__________________
Jack W Smith
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05-17-2004, 10:24 PM
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Banned
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Join Date: Oct 2003
Location: Yorba Linda,
CA
Cobra Make, Engine: SPF w/392CI stroker
Posts: 3,293
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Not Ranked
Jack, thanks!
Okay....I'm pulling a little over 2 volts at the tach output, which is good news (should be between 1 and 5 volts). At least that tells me that the MSD box tach function is working. I'm now 99% confident that the tach board is fried and needs rebuilding. I'm sending the unit out tomorrow to "MO-MA Instruments" in Albuquerque, NM for some higher quality "German" circuitry work. It was either that or send it to some outfit in New York (in which 3 people I spoke to there gave me 3 different answers and 3 opinions).
-Deano |
05-18-2004, 10:55 AM
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CC Member
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Join Date: Jan 2002
Location: Northridge,
CA
Cobra Make, Engine: Arntz Cobra
Posts: 1,839
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Deano,
Maybe I can help you with this. But, I need to know more.
What brand of tach is it? Did it ever work? If so, change did you make when it failed? Do you have a ground wire to the body of the tach?
Paul
__________________
"It doesn't have anything on it that doesn't make it go faster."
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05-18-2004, 11:44 AM
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Banned
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Join Date: Oct 2003
Location: Yorba Linda,
CA
Cobra Make, Engine: SPF w/392CI stroker
Posts: 3,293
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Not Ranked
Paul, it's a SPF factory Smiths tach. Worked fine until I disconnected my ignition system (MSD 6AL, etc.) for maintenance. When I buttoned-up the ignition, the tach started to bounce and then it went dead. The tach is wired with one, 5-wire connector plug. I guess it's possible for a bad ground, but the circuit (according to the SPF owners manual) is also shared with other instruments and components. So I don't suspect a ground problem, as all other components are functioning. I have also researched this problem and apparently it's hit or miss with Smiths tachs and MSD ignitions. The tach has a weak circuit board and is prone to failure from voltage spikes.
The new circuit board that I'm having installed will allow me to bypass the MSD box altogether and go straight to the (-) side of the coil (as was factory installed).
-Deano
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05-18-2004, 03:24 PM
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CC Member
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Join Date: Mar 2002
Location: so cal,
Cal
Cobra Make, Engine: I used to fix them for a living
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I never (or very rarely and don't recall) seeing a fried Smiths tach from use with an MSD, I have seen plenty that just plain didn't work with an MSD, until an extra capacitor and tach adapter were added.
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In a fit of 16 year old genius, I looked down through the carb while cranking it to see if fuel was flowing, and it was. Flowing straight up in a vapor cloud, around my head, on fire.
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05-18-2004, 03:47 PM
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Banned
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Join Date: Oct 2003
Location: Yorba Linda,
CA
Cobra Make, Engine: SPF w/392CI stroker
Posts: 3,293
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Not sure what is going on with the tach, but it no worky. Now if I get it back from MO-MA's in 2-3 weeks and it still doesn't work, then I'm going to be real peeezzzed off..... |
05-18-2004, 04:03 PM
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CC Member
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Join Date: Jan 2002
Location: Northridge,
CA
Cobra Make, Engine: Arntz Cobra
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Deano,
I suppose you've read the MSD manual. If not you can see it here: http://www.msdignition.com/pdf/6series.pdf
I have no experience with Smiths gauges, but I have a lot of faith in MSD products. They offer two adapters which are mentioned in the manual. One for magnetic pickups and another for white wire connections. Thats the way I'd go before sending the gauge off somewhere.
In any case, I wish you luck,
Paul
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"It doesn't have anything on it that doesn't make it go faster."
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05-18-2004, 04:07 PM
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Banned
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Join Date: Oct 2003
Location: Yorba Linda,
CA
Cobra Make, Engine: SPF w/392CI stroker
Posts: 3,293
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Not Ranked
Paul, I've read the manuals and had MSD on the phone at least 3-4 times. I bought their recommended tach adapter and still no luck. The MSD unit is sending a signal, and I trust a brand new tach adapter, so I'm left with having the tach diagnostically checked and repaired (if warranted). Thanks for the encouragement!
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05-18-2004, 04:11 PM
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CC Member
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Join Date: Jan 2002
Location: Northridge,
CA
Cobra Make, Engine: Arntz Cobra
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Deano,
Electronics has been my profession and hobby for 30 odd years. If that tach doesn't work when it gets back, bring it over and we'll get out the BIG hammer!
Paul
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"It doesn't have anything on it that doesn't make it go faster."
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05-18-2004, 04:14 PM
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Banned
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Join Date: Oct 2003
Location: Yorba Linda,
CA
Cobra Make, Engine: SPF w/392CI stroker
Posts: 3,293
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Deal!!! LOL
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05-18-2004, 07:08 PM
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Senior Club Cobra Member
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Join Date: Jun 2003
Location: Lockeford,
CA
Cobra Make, Engine: Midstates, Genesis 427 S/O
Posts: 300
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Not Ranked
Deano,
You said you have a cluster plug? More than likely, you do have a ground in that, don't assume it's good just because all the other instruments are working. Does your voltmeter have the ability to check ohms? If so, take a reading from the ground in the cluster (black wire) to another ground. You should read 0-2 ohms if the circuits good. They teach us that electricity flows, but the truth is , it stumbles around like a drunken sailor. Let me know what you find.
Chris
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Ephesians 2:8
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05-18-2004, 09:13 PM
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Banned
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Join Date: Oct 2003
Location: Yorba Linda,
CA
Cobra Make, Engine: SPF w/392CI stroker
Posts: 3,293
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Not Ranked
Chris, I'll have to check it out and report back to this thread. Can't get to it this evening though....maybe tomorrow.
THANKS for the tip!  |
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