GQ TD42 using standard ignition-type tacho

[spektrum]

Hi Patch,

Thanks for the reply. I had thought it might just be picky about the input signal. It used to work when I had the petrol engine, but since then I have tried so many things to get it working I have no idea if I damaged the unit.

Where did you place your variable resistor? Did you place the variable resistor in series with the wire to the tacho, or as a pull-up resistor?

I noticed there is already a resistor in series with the signal (see circuit below). This resistor is positioned in the engine bay near the back of the radiator reserve, cable-tied to the ignition coil wiring loom. I tried with and without this resistor.

[patch697]

I just dropped the trim pot resistor in series with the signal wire. I actually removed the resistor you have marcked in your pic & used it in place of.

That resistor marked above is located only a few inches from the ignition coil in the loom heading back to the inner guard if that helps you in any way to locate for yourself.

[spektrum]

Yeah I had already found it. I will try it tonight.

Which ignition system did you install that caused issues with the tacho? When I had the TB42, I removed the points and put in a Petronix unit. I didn't have any issues with this, but it sound like you put in something with a bit more kick.

I'm not sure why these tacho's are so picky, I would have thought the circuit would be simple ... just a frequency counter triggered by the falling edge of the signal wire. Maybe levels are not high or low enough .. or duty cycle? I need a CRO to analyse the signal from the ignition coil VS. the converter I have.

[patch697]

Yeah I had already found it. I will try it tonight.

Which ignition system did you install that caused issues with the tacho? When I had the TB42, I removed the points and put in a Petronix unit. I didn't have any issues with this, but it sound like you put in something with a bit more kick.

I'm not sure why these tacho's are so picky, I would have thought the circuit would be simple ... just a frequency counter triggered by the falling edge of the signal wire. Maybe levels are not high or low enough .. or duty cycle? I need a CRO to analyse the signal from the ignition coil VS. the converter I have.

I used a Crane Cams multi spark CD amplifier with a mag trigger setup out of an RB30 I fabed up for the TB42 dizzy & dropped ICE ignitions leads & coil on top for good measure.

A CRO would be bloody handy just to get the signal data.... We could build a convertor of our own thats spot on for the job that way but I don't have one laying around anymore nor the bucks to just go pick one up....lol

P.s. A signal gen would go down a treat as well......hahahahahah

[spektrum]

I have a signal generator here, but the Nissan tacho doesn't like this signal either. But my signal generator can only vary frequency and duty-cycle. It cant change the amplitude.

The diesel converter I'm using is is a Dakota Digital DSL-1. The output signal works on my handheld tach/dwell meter.
http://www.dakotadigital.com/index.c...rod/prd128.htm

It has 2 types of outputs .. standard and high voltage. The standard outputs produces a voltage pulse signal from 0 to 12 volts. The high voltage produces 6 to 18 volts -- they told me some tachometers need the extra voltage to trigger. Neither work...

I'll try the variable resistor tonight. Will be good if it works...

[patch697]

I have a signal generator here, but the Nissan tacho doesn't like this signal either. But my signal generator can only vary frequency and duty-cycle. It cant change the amplitude.

The diesel converter I'm using is is a Dakota Digital DSL-1. The output signal works on my handheld tach/dwell meter.
http://www.dakotadigital.com/index.c...rod/prd128.htm

It has 2 types of outputs .. standard and high voltage. The standard outputs produces a voltage pulse signal from 0 to 12 volts. The high voltage produces 6 to 18 volts -- they told me some tachometers need the extra voltage to trigger. Neither work...

I'll try the variable resistor tonight. Will be good if it works...

I'd say at a guess the 18v input is for 24v systems so I hope you didn't pop yours when you gave it the extra juice.

[spektrum]

I had been using the Normal Output for a few nights before trying the high-volt output. Hopefully by testing the High-Voltage output hasn't compounded the problem. The information that came with the unit is a bit sparse regarding the normal and high output.

Maybe it would just be easier to buy a cluster from a diesel vehicle and swap out the tach gauge.

[patch697]

I had been using the Normal Output for a few nights, and it didn't work. Hopefully by testing the High-Voltage output hasn't compounded the problem. The information that came with the unit is a bit sparse regarding the normal and high output.

Maybe it would just be easier to buy a cluster from a diesel vehicle and swap out the tach gauge.

Yes your probably right but where is the challenge in that???........lol

[spektrum]

That's true. Just hope I'm not wasting time with a damaged tacho gauge.

Out of interest, the petrol tach gauge is marked serial number "XP-728E". What is the serial number of the gauge for the TD42, the version that has the sensor connected directly to the gauge (not via the glow controller). "97_gq_lwb" did you see the serial number when you did the gauge change-over?

[spektrum]

I give up. Tried everything to get this working, but it just doesn't want to work. There is every chance I have damaged the input circuitry in the tacho.

Just bought a tacho from the wreckers that suits the TD42. Will fit it later this week. Looking at the circuit diagram (TD42), there are 2 wires from the sensor direct to the tacho ... but if you look on the back of the cluster, one of them is just GND. Therefore I should be able to just ground one wire from the sensor, and connect the other to the existing loom.