Tach not functioning

[Six_Shooter]

I haven't forgot about this thread...

I just haven't had time to get the test equipment setup on the bench. I just got it setup, and I built the circuit lined out in the MS2 V3.0 manual on a breadboard and using my function generator the circuit works and definitely needs a pull up resistor. The spec'd 1K resistor works fine on my bench setup using a 280Z tach with the input resistor bypassed, I have not tried it without the resistor bypassed. This is not connected to an MS, but I'm sure it will work just the same, since the output from the MS CPU should be just a pulsed output similar to what my function generator is doing. I do plan to connect an MS to this, but I expect the same results.

The circuit I used is this one: http://www.msextra.com/doc/pdf/html/MS2 ... .4-41.html

[Six_Shooter]

I just connected the above circuit to an MS1 V3.0 (it was the easiest to get going quickly), and the 280Z tach works just the same as it did when the circuit was being triggered by the function generator. The circuit is still on a breadbpard. There is a small issue in that I mentioned previously that above a certain RPM the tach will drop to 0 because the duty cycle of the signal is too long. If that is an issue once you get your tach working I can draw out the circuit I used. I just made it on some prototyping circuit board and attached it behind the tach. The circuit I made ensures that the signal is always very short on the positive pulse, IIRC it was around 10% DC and works well beyond what the tach is actually capable of reading.

I can't tell you exactly RPM it is that the tach will drop to zero, because in testing tonight I was reminded that this tach is not in my car because it's not very accurate, I can get it to read well at low RPM, but at higher RPM it reads a higher RPM than what the RPM actually is, or read accurtaly at higher RPM, but low at low RPM. The tach I have in my car also a 280Z tach reads quite accurately.

[DaveEFI]

Just some info. My Rover SD1 has a Smiths rev-counter originally triggered by the single coil. After going EDIS, I tried all the circuits given here with mixed results. None matched the RPM readings on TS, or related to road speed as well as originally, and were non linear.
The Smiths unit on this car is open frame so easy to work on. I obtained a spare, and replaced the head electronics with a chip designed for such things, which also allowed easy adjustment of the reading. And triggers direct from MS or the EDIS module.

Just how difficult this is would depend on your individual tach head - some can be tricky to dismantle.

[Davek]

Glad to hear your set-up works for you. It could only mean my 280z tach or MS is not functioning correctly.
Attempted to get my 73 tach out of the dash and had little success. Those darn wing nuts are tight when you need body contorting to even see the nuts. Will get it out this weekend and try the old tach as mentioned in my other thread.
I did try the replay as described but did not work either. Did heat up a component on the tach. Darn hot.

[Davek]

Just pulled the tach out of my 6/73 body Z. d*** if isn't the later model design tach. I was really hoping for the older design.
What a bitch to remove. It will never go back in and be secured without pulling the dash.
I'll disassemble the tach and report back using MS3X a 1k pull-up resistor and bypassing the internal resistor.
cheers

[Six_Shooter]

You want the later design anyway. The earlier design requires an adapter to not limit power to the coils, if powering teh coils from it would work, sometimes it does, most times it doesn't.

[Davek]

OK, hooked up the tach from my car using a 330ohm pullup bypassing the tach resistor. The tach did not move. I don't have 1k resistor. only a 330 & 2.2k.
The component on the tach markes 30ohm got very quickly. I checked for this as the 76 tach I have did the same thing. I disconnected power before it got hot enough I hand to let go. About 8-10 seconds.
I then connected 12v power & ground to the tach with no MS tacho signal at all to the tach(only the 2 wires) 12.5 actual supply voltage. That 30ohm component got hot same as with tach signal w/pullup.
any thoughts.
see picture showing the 30ohn component.

[Davek]

rechecked the 2 wire hook up with my multimeter and reads 0.38 amps.

[Davek]

heres the tach pic showing 30ohm component

[Six_Shooter]

rechecked the 2 wire hook up with my multimeter and reads 0.38 amps.

What exactly were you checking here?

How did you connect the multimeter?

That resistor probably will get a bit warm, which is why it's physically large to dissipate that heat.

I'll turn mine on for a bit and see what happens, I'll do it with no input signal and if the resistor doesn't get warm with that I'll put an input into it.

Are you sure you're connecting the polarity correct for the 12V power?

[Davek]

12V to red wire.
Multimeter connected as this--- 12v red lead thru multimeter to black lead to tach positive. ground to ground. Red wire Pin on multimeter to 10a max .
I checked voltage at the dash--11.58
maybe it will get hot and stabilizes?

[Davek]

Hey Six
did you get a chance to turn yours on for a while ? too hot to touch or did it hit a spot and stay there. No smoke:)

[Six_Shooter]

I haven't been able to test with an input signal to the tach, but I did leave the tach powered up and on for a while and the 30 ohm resistor never got too hot to touch.

[Davek]

My buddy loaned me 2 aftermarket tachometers today. One was off about 500 rpm. Did not spend any time with it. The other was spot on. I'm really pleased to know the problem is not my MS3X.

Six, you sound like a busy man but was wondering if I could send my Datsun tach to you for you to make it come alive?
Dave

[Six_Shooter]

That's good to hear.

At this point, no, I would not be able to get to them very soon. I'm working on making a proper replacement circuit that replace the circuit board, slowly, far slower than I would like to be, just too many projects, not enough time. This is mostly for my own personal satisfaction. There is a circuit available from someone, I can't recall off the top of my head and will have to dig a bit to find it that replaces the entire circuit inside the tach, that might be a better option for you. I want to say they are based in Australia.

I have a spare tach that works, but reads incorrectly, I have not been able to reverse engineer the OEM circuit board due to a few of the items being proprietary hybrid circuits, these could have anything inside them. So it would be nice to have it work correctly, which is why I've been working at this so slowly, I have a good working tach in my car...

[Davek]

Hello Six_ Shooter and all following this thread.
I have a functional tachometer now.
I ended up buying a SunPro2 tach. $30 delivered. It works great with my MS3X. The SunPro has an 0-8000 rpm face with same sweep as my Datsun late 240 early 280z tach face.
I pulled the guts from the SunPro and fitted them to my stock tach housing. Not much work if you have stuff to work with. Drills, epoxy wiring tools etc.
I have not driven yet but up to 3,000 rpm it matched MS3X. Saturday is the test drive.

I did epoxy my old needle/indicator pointer to the SunPro center piece. My needle is heavier than the short plastic Sunpro needle. I did move the needle around to match rpm's as engine was idling(tuned the needle position). My concern is when the needle swings over the top to 5,000 rpm will the needle fall from weight and read incorrectly. If this happens I'll make a needle out of Styrofoam.

Thanks again for all the support.
Dave

[jasaircraft]

Hello guys i'm on the same struggle atm.
Where is that resistor that has to be bypassed?
Im trying to use the ms3x tacho output.