Thread: Tach Woes, Too

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Along with the battery woes, about a month back I noticed that my AutoMeter tach was reading about 300 to 400rpm low at cruise speed with the error diminishing as rpm decreased, only off about 100rpm at idle speeds. I talked to AutoMeter, they convinced me to send it in to be checked, and they found it to be out of calibration, but also out of warranty - I purchased the gauge set in March 2010 for the build, first calibrated the speedometer in November 2010, so even considering the "first used" date I exceeded the one year warranty. $25 plus $13 shipping brought me a re-calibrated tach and all was good. That is, until we got 30 miles into the Springfield road trip and the tach dropped from 2000 to 1500, then to 1000, then to 500rpm all in about ten seconds. It bounced around in the 400 to 800 range for about 100 miles, and then started a liesurely climb back to 2000, and seemed to be dead on for the rest of the weekend. As we left Springfield it was fine for about ten miles, then lost about 500rpm and stayed there for most of the trip. As we neared home it again seemed to regain accuracy.

It's on its way back to AutoMeter today. I explained that I was already into the repairs about $40 on a $100 instrument, and they've said that if they find it to be bad they may offer a replacement at "a significant savings", so I decided it was worth the $3 USPS Priority Mail charge to see what they say....

I'd venture to say that they replaced the circuit board, doubt if they replaced individual component(s), and you ended up with another defective board. The only other thing I can think of that could cause your problem would be voltage spikes from your ignition.

Originally Posted by NTFDAY

I'd venture to say that they replaced the circuit board, doubt if they replaced individual component(s), and you ended up with another defective board. The only other thing I can think of that could cause your problem would be voltage spikes from your ignition.

Ken,
They said they did not replace anything, saying that it was simply "out of calibration" which made it sound like a potentiometer adjustment or something similar, but they told me that the adjustment could not be made without totally disassembling the unit. I asked what would cause the tach to go "out of cal" after operating for a year dead on, and the tech said that he did not see anything in the documentation to point to anything specific, but he did mention the possibility of voltage spikes causing problems, like "...charging the battery without disconnecting a cable". I believe that I have a component that is bad, or that goes out of range with time/heat, and then after a period may cool or ??? I'm hoping they offer me a new one at cost, as I really want to keep a matching set of gauges, and buying the six gauge set again would be the pits!!

Makes sense to have a pot on the board to calibrate at the factory and if was out of calibration when they got it back that tells me that a component(s) is severely out of tolerance. That could be caused by a voltage spike and if that is the case the tach does not have that protection built in. You might ask if they have a kit that will eliminate that possibility.

Originally Posted by NTFDAY

Makes sense to have a pot on the board to calibrate at the factory and if was out of calibration when they got it back that tells me that a component(s) is severely out of tolerance. That could be caused by a voltage spike and if that is the case the tach does not have that protection built in. You might ask if they have a kit that will eliminate that possibility.

That's a good suggestion. I may pose that question to the tech's when they come back with their ideas.

A tach should not "go out of cal" in its useful life....sounds like a brush off by a
phone tech....or they know there's a problem and use the cal as an excuse.

I am interested in what model Auto meter tach you talking about?

Model 1297 Old Tyme Black Old Tyme Black Electric Tachometer

Originally Posted by rspears

Ken,
I asked what would cause the tach to go "out of cal" after operating for a year dead on, and the tech said that he did not see anything in the documentation to point to anything specific, but he did mention the possibility of voltage spikes causing problems, like "...charging the battery without disconnecting a cable".

Spikes usually take the sensitive components out completely ceasing to work at all from that point on.

Intermittent electronic problems are almost always caused by a bad connection on or at the circuit board. Most times it is a poor solder connection of a component to the board or a damaged trace, sometimes it is a cracked circuit board.

Also you should check with your States consumer affairs, your State may give you legal rights beyond the manufacturers warranty.

Originally Posted by 36 sedan

Spikes usually take the sensitive components out completely ceasing to work at all from that point on.

Intermittent electronic problems are almost always caused by a bad connection on or at the circuit board. Most times it is a poor solder connection of a component to the board or a damaged trace, sometimes it is a cracked circuit board.

Also you should check with your States consumer affairs, your State may give you legal rights beyond the manufacturers warranty.

I think your analysis is right, and at this point if the fix is not obvious I'm hoping for an offer of a new unit at or near cost. What you say about the consumer affairs office is a good thing to remember, but in this case I'm only looking at a nominal $100 instrument, and looking at the hole in the dash will get old really quickly, and going through the State would likely be an extended process.

I had a very good experience with Autometer regarding a digital tach/shift light. It began losing LED bars. When I called them, one of the tech guys knew what was wrong with it, and he told me to send it back. I was sent a new one free of charge. I told him I got it from JEGS more than a year previous, but they replaced it anyway.

I had a big face tach back in 1985 in my Big Block Dodge Charger.
It had a built in Rev limiter, and while driving around the car just started shutting down.
At first I thought the fuel pump was vapor locking.
But after chacking that out it was not the problem, so I disconnected the tach.
And it stopped cutting off, so I opened the tach and found the board in that was cracked.
Just like the other guys on here said about yours. It really sucked because I had built
a whole floor concel around the thing with speakers in the sides and a couple cup holders.
Kurt

Would a points condenser to ground, on the hot wire, protect it from spikes?

I was wondering the same thing!!!

Originally Posted by firebird77clone

Would a points condenser to ground, on the hot wire, protect it from spikes?

No, but a zener diode would