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Discussion Starter · #1 ·
Dear Alfa friends, best wishes and happy new year.
My name is Andrea and I have a strong passion for both electronics and cars ...
I ask for your help because I would like to repair the spider alfa romeo third series aerodynamic tachometer (1985).

I try to describe what I discovered:
the instrument is stopped, although a signal is injected into the signal terminal, the needle does not move.
I tried to replace the electrolytic capacitors but doesn't work.
I started a series of measurements, I checked the nominal value of the resistors, the trimmer and the capacitors were ok.
I detected an excessive current absorption (170mA) at rest (key condition inserted, contact on but engine off), in this condition the 82 ohm resistor heats up very much; this absorption disappears if I unsalted pin 7 of the integrated SN29736P.
I did not find any documentation and spare parts for the SN29736P IC... I found spare parts for the SN29736P1 IC... (from China ??)
Could the SAK215 IC, mounted in the spider duetto IV serie tachometer, be it replacement?
Do you have any advice on this?
Since I'm for information ... do you have any news of the actuator, motor, that moves the needle? Do you have a code? Can it be found as a spare part?
I know the questions are many ... my experience little ... I rely on your patience.
Hoping to read your answer, thank you
Andrea

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Discussion Starter · #3 ·
Thanks for your attention ... I'll try even if I tried to move it, put it out of calibration, and in any case the needle does not show signs of movement. The resistance continues to heat up

I measured the trimmer with the tester ... but, anyway, I'll change it.


The trimmer/potentiometer is often intermittent. Try a trim pot cleaner or maybe replace it. 0-100 Ohm will do.
 

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1988 Spider Quadrifoglio
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576 Posts
On the "monopod" Jaeger gauges, the mounting posts double as the power and signal terminals. I found that the connection between the mounting posts and the circuit board can also be a problem. I fixed it by running jumper wires between the posts and the circuit board.

The tachometer is not difficult to recalibrate. All you need is a digital multimeter w/ tachometer function attached across the ignition coil primary, and extension wires so you can connect the tachometer to the gauge cluster. Then start the car and adjust the trim pot to read the same as your multimeter.

If you don't have a multimeter with a tachometer function, you can use the frequency function and a bit of arithmetic.

Good luck!
 

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Discussion Starter · #5 ·
On the "monopod" Jaeger gauges, the mounting posts double as the power and signal terminals. I found that the connection between the mounting posts and the circuit board can also be a problem. I fixed it by running jumper wires between the posts and the circuit board.

The tachometer is not difficult to recalibrate. All you need is a digital multimeter w/ tachometer function attached across the ignition coil primary, and extension wires so you can connect the tachometer to the gauge cluster. Then start the car and adjust the trim pot to read the same as your multimeter.

If you don't have a multimeter with a tachometer function, you can use the frequency function and a bit of arithmetic.

Good luck!
You are absolutely right, I noticed that if the printed panel of the counter moves, the pilot signal of the instrument is short-circuited. I will isolate him.
Today I went ahead with the analysis. I replaced ic SN29736P with SAK215, I also checked the trimmer but it doesn't work. The only certainty is, that at rest, the circuit absorbs less than 50 mA, the resistor does not heat up.
The voltmeter, the motor that manages the indication, has a resistance of 300 Kohm; even if it is powered at 12V, it barely moves (about 2 teeth). This makes me think it's broken.
It is not a problem to calibrate it, I have an oscilloscope, signal generator, laser RPM counter ... I apply the mathematical formula ...
I miss where to buy parts.
Do you have any idea where I can buy motor and IC? Thank you
 

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1988 Spider Quadrifoglio
Joined
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576 Posts
You are absolutely right, I noticed that if the printed panel of the counter moves, the pilot signal of the instrument is short-circuited. I will isolate him.
Today I went ahead with the analysis. I replaced ic SN29736P with SAK215, I also checked the trimmer but it doesn't work. The only certainty is, that at rest, the circuit absorbs less than 50 mA, the resistor does not heat up.
The voltmeter, the motor that manages the indication, has a resistance of 300 Kohm; even if it is powered at 12V, it barely moves (about 2 teeth). This makes me think it's broken.
It is not a problem to calibrate it, I have an oscilloscope, signal generator, laser RPM counter ... I apply the mathematical formula ...
I miss where to buy parts.
Do you have any idea where I can buy motor and IC? Thank you
Sorry no. Try posting on the parts forum, maybe someone has a spare non-functional tachometer lying about that you can use for parts? Or maybe a working one!

Is the motor shaft seized or sticky? Maybe there's been a bit of corrosion or debris build-up in the motor bearing?
 

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Discussion Starter · #7 ·
Sorry no. Try posting on the parts forum, maybe someone has a spare non-functional tachometer lying about that you can use for parts? Or maybe a working one!

Is the motor shaft seized or sticky? Maybe there's been a bit of corrosion or debris build-up in the motor bearing?
Thanks for your attention, the crankshaft is free ... I think it is the coil that no longer works ... together with the integrated ... If I feed, as it should be, the 12V actuator moves only two teeth (100 rpm) ... 12 V from the battery to the motor ... a little bit. I write the announcement in the spare parts section ... If anyone has more information ... welcome! Thank you.

Andrea
 

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Discussion Starter · #10 ·
Dear Alfa friends, best wishes and happy new year.
My name is Andrea and I have a strong passion for both electronics and cars ...
I ask for your help because I would like to repair the spider alfa romeo third series aerodynamic tachometer (1985).

I try to describe what I discovered:
the instrument is stopped, although a signal is injected into the signal terminal, the needle does not move.
I tried to replace the electrolytic capacitors but doesn't work.
I started a series of measurements, I checked the nominal value of the resistors, the trimmer and the capacitors were ok.
I detected an excessive current absorption (170mA) at rest (key condition inserted, contact on but engine off), in this condition the 82 ohm resistor heats up very much; this absorption disappears if I unsalted pin 7 of the integrated SN29736P.
I did not find any documentation and spare parts for the SN29736P IC... I found spare parts for the SN29736P1 IC... (from China ??)
Could the SAK215 IC, mounted in the spider duetto IV serie tachometer, be it replacement?
Do you have any advice on this?
Since I'm for information ... do you have any news of the actuator, motor, that moves the needle? Do you have a code? Can it be found as a spare part?
I know the questions are many ... my experience little ... I rely on your patience.
Hoping to read your answer, thank you
Andrea

View attachment 1716633 View attachment 1716634
I have restored this tachometer... for more video see my youtube channel...
 
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