Trouble shooting 123 dizzy

Technical advice Q&A

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#21 Re: Trouble shooting 123 dizzy

Post by rswaffie » Fri Jan 11, 2019 8:54 pm

Cheers Tom.
I’m going to do a complete check of the ignition and charging circuits before I put the dizzy back as I can’t help thinking that some of the recent electrical issues I’ve had seem to have occurred since connecting the dynator through the relay to the ignition light.

S1 3.8 FHC Opalescent Golden Sand 889504
Undergoing a comprehensive restoration in my small, but utilitarian garage :wrench: :hammer: :fingerscrossed:

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#22 Re: Trouble shooting 123 dizzy

Post by JagWaugh » Sat Jan 12, 2019 7:57 am

Tom W wrote:
Fri Jan 11, 2019 8:21 pm
My 123 wasn’t good to 20v. At about 15v, it causes the ignition to cut out, thought it doesn’t seem to have caused any permanent damage. I had a faulty relay in the alternator circuit, this caused the regulator to see a lower voltage than the alternator was putting out, and concequently the car got overcharged.
As I understand it they have built it to handle up to 20(ish)V without permanent damage. What happens when the voltage goes too high is that the CPU does a reset, and can miss a spark for the brief period that restart takes.

I had a problem with a TR3A to which we'd fitted a 123/tune to. It ran flawlessly while standing still and revving through rpms (We put an ignition scope on it and it was perfect), but as soon as you took it out on the road it would cough just briefly about every 8-10 minutes.

Once we jury rigged a separate battery to run just the ignition the cough went away. Then I read somewhere that the 123 will reboot under overvoltage conditions.

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