[V8] Tach drop out

[dsaad at icehouse.net]

If it gets to the point where someone needs one, I will take a look at it.
The electronics for it are pretty simple - usually.
In fact, for a cheapo tach, the "electronics" is just a capacitor and a
resistor.
These are not cheapo though. In fact, I think they are very nicely made and as I
recall, there is a frequency to voltage converter IC chip inside. If this is
what failed, it would have to be an off-the-shelf part to be repairable.
If the meter movement itself is bad though you are SOL.

You can probably do some experiments here too to determine the problem.
If you can identify the two meter contacts, preferably seperate them from the
circuit board and apply a small current controlled voltage to the terminals.
If you can make the needle swing then it is probably OK - indicating the circuit
board is bad.
For a voltage source, a AA battery with a series resistor (maybe 100 ohm?)
should work.

Dave

Quoting Ingo Rautenberg <i.rautenberg at waratap.com>:

> Possibly.  But in my experience, the tach is the only gauge I've seen in
> these cars that actually "goes bad." ..and the only one I've had to replace.
> I still have the bad one from mom's first V8 if anyone wants to experiment
> with it : )
>
> Best of luck,
>
> Ingo
> ----- Original Message -----
> From: <dsaad at icehouse.net>
> To: <v8 at audifans.com>
> Sent: Friday, August 25, 2006 10:25 AM
> Subject: Re: [V8] Tach drop out
>
>
> > This smells like a connection problem in the IC to me.
> > I don't have the schematics in front of me, but if you have the schematics
> and
> > can follow them, and can use a volt meter, you should be able to locate
> the
> > problem.
> >
> > First, locate the signal source. This is almost certainly the ECU, and it
> is
> > probably a pulsing signal - so it will be hard to measure with an ordinary
> meter
> > but if yours can read frequency then you are good. The tach is responsible
> for
> > turning this pulse into a voltage for display - the tach is really just a
> volt
> > meter, as is the speedo. They both work the same way, only the frequency
> of the
> > signal is different.
> >
> > (btw, I went through this same procedure to identify my bad speedo sensor)
> >
> > You will need to attach your meter to the signal at the ECU and monitor it
> while
> > driving, or do whatever needs to be done to make it fail. If the signal
> drops
> > out then you have an ECU problem. (I really doubt this - it is just the
> first
> > step)
> > If everything is OK, it is time to pull apart the IC and attach the meter
> right
> > at the tach terminal - you may need to solder here. If the signal drops
> out, you
> > have a connection problem. If not you still have to verify the 12V and
> ground
> > supply to the tach but most likely there is a broken wire or intermittant
> > connection. I found the interconnect wires between the IC sections were
> cracked
> > on mine. There is a design weekness (IMHO) where the interconnect ribbon
> cables
> > can vibrate and crack over time.
> >
> >
> > Dave
> >
> >
> > Quoting Mike Del Tergo <mdeltergo at hotmail.com>:
> >
> > > That will keep you busy. On the tach I don't know if it is the IC as I
> have
> > > "fixed" that.  Suddenly, it will go to zero (or not come on) and stay
> there
> > > only coming on intermittantly.  Others have said these can go bad, but
> no
> > > one seems to have a way to check if it is the tach or wiring.
> > > Mike
> > > PS had to go to a wrench to get the O2 off but all seems good now.
> > >
> > > >  Mike sorry I haven't gotten back but I was doing my
> > > >T-belt on my Green 93 v8 & the Euros, & the 2benn coil
> > > >overs & stuff ready for //sfest. I'm just doing a few
> > > >more things beforhand but I will check to see if I
> > > >have a tach. Whats wrong with the tach?? I all so have
> > > >to search around for the armrest strut.
> > > >I'll get back to you tomorrow
> > > >Thanx
> > > >Ron
> > > >
> > >
> > >
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