Im repairing this circuit, the transistor was torched and all markings burnt away so I'm just taking a guess at what to replace with. I can't figure out what should be gate, collector and emitter though, what is this circuit is trying to acheive?.. my hunch is the 18V with the 15 ohm resistor is for the gate, and the op amp connects to collector but I still don't see why.
Is anyone familiar with this kind of schematic?

https://drive.google.com/file/d/0B24ZN7xs6vYKM3VnUk1kampXQlU/view?usp=sharing

https://drive.google.com/file/d/0B24ZN7xs6vYKM3VEMEptckt3NXM/view?usp=sharing

Seems to have something to do with charging a 6V back-up battery, it went flat and that's how I found the burnt transistor. So I'm thinking the OP amp may be something like a voltage to current converter???

http://www.allaboutcircuits.com/vol_3/chpt_8/7.html

 

Have you tried contacting the company? Forma is now handled by Thermo Scientific.

Ken

 

Hola cam

For starters: it is collector, base & emitter OR drain, gate & source.

Not digged yet at all in your schematic; please recheck carefully all around the LM10.

What that circuit does?

 

Have you tried contacting the company? Forma is now handled by Thermo Scientific.

Ken

Interesting.. there's a Thermo Scientific across the road from me, although I know they don't make these freezers anymore.. I'll ask them on Monday thanks.

Hola cam

For starters: it is collector, base & emitter OR drain, gate & source.

Not digged yet at all in your schematic; please recheck carefully all around the LM10.

What that circuit does?

I'll recheck around LM10, there's more i could include in my diagram so i should do that again too.

 

Could it have been a LM7805 or some other 3-pin regulator instead of a transistor?

 

Could it have been a LM7805 or some other 3-pin regulator instead of a transistor?

That's what I thought too but the PCB is labelled with a Q at that location same as the other transistors, the regulators are labelled with U.

 

Update:
So I have just returned to this repair, I replaced the damaged transistor with a PNP (TIP32C) power transistor. The comparator output to the base, as I'd found this type of schematic on a lot of battery charger circuits just from google image search. It's float charging the battery and I'm not getting any alarms as yet. Thanks for discussing this with me, I know my schematic was useless, there was a relay in there that is switched by the transistor.
Thanks again!