Brand New CDI for CB400T/CM400T/CM400E/CM400C/CB450SC

Hey all, I was wondering... Does anyone know the purpose of TH1 at the gate of SCR1 in the circuit? I would think it is a PTC thermistor? Does it provide some sort of protection?
 
If temp goes up on the SCR, higher current would go to the gate? I'm not use to SCR's. What effect does that then have on the SCR's behavior? A shorter pulse?
 
An SCR datasheet shows trigger voltage changes from 1.0v to say 0.5v from 25C to 100C The thermistor is a shunt to ground here, it's hard to see because ground is not easy to see in schematic, it's the green coil wire. So when NTC heats up it's resistance goes down and it pulls the signal down to match. We have 3 signals combined to trigger SCR. This F15 to start, then Advance Pulse wave to advance before F15 with higher RPM. F43 acts as a limiter to avoid advancing any further. It's a complex analog circuit, so it's somewhat hard to speculate on it without testing, but I suspect the Advance Pulse overtaking the F15 signal is the most sensitive part that might benefit from the temp compensation.
 
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Ah I understand now! Thank you very much for the detailed response. I was missing the path to ground.
 
To all who have tried to inquire about a CDI from Frank - he is going through a very difficult time right now, so please respect his need to disconnect for the moment.

Please PM me for further information and expected potential delivery times.
 
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