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Supply line circuit tracking for intermittents

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Scooty-T

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Hello all,

I am a newbie to the forums to as of today. I couldn't figure out as to what forum I should ask this, so I placed it here.

I took some electronics in high school 67-68 but never carried through with the field. Through circumstance I ended up the auto repair business. I embraced the adoption of electronics in cars and specialized in diagnostics. Since the ECU did not allow board level repair and paying customers could not afford re-inventing the wheel, repairs were mainly, isolate the offender and replace the component and/or repair wiring. I also wrote for an auto mag in Canada for 6 years as it was a way for me to keep myself thinking. I have been out ot the repair game for 20 years now.

I have been engaged to try and track down an issue with a 70's car with Y2K technology onboard. Because it has no so called "codes" capability but some data recording ability, there is some hope.

The issue is "intermittent" loss of electrical power and thusly engine power. Tracking the numerous wires in the car is a tedious undertaking. Had a Fluke 97 years ago but burned it up on an engine dyno 10 years ago. I now have a Rigol DS1054 which is years ahead of the 97 in all but one area, portability.

My thoughts are now, to come up with a go/no go piece of equipment. I require something that will "latch" when a condition happens. I would not be monitoring signals only supply voltage.

The requirements are:

1) To have the ability to monitor chassis power, 12-15.3V and ECU supply 5-5.1V.

2) To also monitor ground or return side circuitry

The test unit would have its own power supply, hopefully 5-6V.

Monitoring system should hopefully have high impedance as the 5V rails on most cars are restricted to approximately 50mA system power.

Supply side and low V monitoring would be done on a switchable gang basis. By this, I mean that I would not monitoring 12 & 5V systems at the same time.

However, the latching/monitoring components should be the same and just have some "switched in" circuitry for the 5 & 12V and the high/low side testing. This is why I am thinking the low internal operating V supply.

I have a 74HCT14 chip (packaged in 1999 from RadShack) for doing inversion and some BJT's and MOSFET'S.

I would like to use LED's for the indicators. I have RED/GREEN combo units that I used to use for logic probes years back.

The theory would be to have a latching set up so as to not have an auto reset if the intermittent miraculously "fixed" itself.

This car only has problems after being driven for 20 minutes or more. When it quits it may restart immediately or we have to sit and wait. Doing diagnostics on the side of the road is dicey.

If I have placed this in the wrong forum, please speak up and direct me. Age is showing its down points.

Sorry for the long wind, but if its any consolation I did shorten it some.
 
My Ford Fiesta assembled in Brazil used to go into a complete black out as you describe in any possible condition when underway.
It took 1 nonth and nothing less than 2.000 Km for the factory to report that it was a failed connector.
They played all the tricks to not provide me any proof of the problem.
Bad recollections.
 
The obvious solution is to use a microcontroller, and program it to do as you wish - you could easily use the Arduino Uno development board to make a device to do what you need.
 
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