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JBC Soldering Station CD-2BC - Complete Schematic & Analysis

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Icchan:
I was looking through the schematics and I went over the ZCD and I just can't understand how it prevents the lower transistor from having Veb breakdown since lower transistor sees negative voltages in excess of -23.5v on the negative half cycle...
Unless there's something I missed?

Since both 23.5v and 12v secondaries have common ground, the AC voltage is swinging between +23.5v and -23.5v in respects to GND... right? :D

It's late at night... I might be overlooking something obvious here.

This seems like a learning opportunity if anyone cares to explain to me what I'm missing here ;D

shangaoren:
there is something i don't get in your schematics of reverse engineering :

i have two tips, one that seems to have the heater fried and the other that works. i tried to put both in hot water, measured voltage and resistance between every pins and this is what i get.

As i understand the results, the common is the tip body, heater is between body and middle pin and thermocouple is between first pin and body, did i miss something ? 

johnmx:

--- Quote from: shangaoren on March 09, 2020, 10:12:50 am ---there is something i don't get in your schematics of reverse engineering :

i have two tips, one that seems to have the heater fried and the other that works. i tried to put both in hot water, measured voltage and resistance between every pins and this is what i get.

As i understand the results, the common is the tip body, heater is between body and middle pin and thermocouple is between first pin and body, did i miss something ? 

--- End quote ---
Are you using a T245?
Other types may have different connections.

A picture is worth a thousand words (see attached).

shangaoren:
Yes, the broken one is a C245-789 and the other one is a c245-911

johnmx:

--- Quote from: shangaoren on March 09, 2020, 11:13:01 am ---Yes, the broken one is a C245-789 and the other one is a c245-911

--- End quote ---
As you can see from the attached picture on my last post, C3 is the common, C2 the heater and C1 the thermocouple.

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