I have spent several hours going over it. I photographed both sides of the board, edge detected the traces, flipped them, made them white and overlaid the component side.
Then manually traced them and drew the schematic. The things connected to REF OUT are the inputs of two different op amp comparators. So it is a voltage reference. Just an odd way to draw/design it. From: Ken Hohhof Sent: Tuesday, December 4, 2018 2:10 PM To: 'AnimalFarm Microwave Users Group' Subject: Re: [AFMUG] OT Linear Circuit Are you sure you drew it right? It’s not making any sense to me, especially with REF OUT being an output. I see a 3V virtual ground, a 100K positive feedback maybe for hysteresis, but that would assume this opamp is acting as a comparator not a reference generator, and REF OUT would be in input, and something else would be the output. I thought maybe this was one of those fancy comparators with a built in reference but an LM324 is just a plain vanilla single supply quad opamp. Maybe once somebody explained how it works we could go aha! why didn’t I see that? But right now it makes no sense to me. Maybe if we saw what was connected to REF OUT. From: AF <af-boun...@af.afmug.com> On Behalf Of ch...@wbmfg.com Sent: Tuesday, December 4, 2018 2:51 PM To: AnimalFarm Microwave Users Group <af@af.afmug.com> Subject: Re: [AFMUG] OT Linear Circuit Nope. The sensor is a different part of the circuit. From: Mark Radabaugh Sent: Tuesday, December 4, 2018 1:41 PM To: AnimalFarm Microwave Users Group Subject: Re: [AFMUG] OT Linear Circuit Seems like one of those resistors is the sensor? To me it looks like the output is going to try to stay just over 3V but will lag ‘ref out’ up or down if there is any voltage on it. I can’t recall if op amps can sink current or not. The wife was annoyed that the contractor blew up the new fan hood for the kitchen remodel with a dead short on the output. A Replacement board was 8 weeks out. “Can’t you get out your special catalog and fix it?”. I suppose - hum.. this circuit board is built to drive more than one fan. Let’s take this SCR out and move it over here, solder a new fuse in here… yep - don’t even need to order parts. Mark On Dec 4, 2018, at 2:43 PM, <ch...@wbmfg.com> <ch...@wbmfg.com> wrote: I am reverse engineering a temp control circuit on an electric tankless hot water heater. Manufacturer says no user replicable parts inside. Oh yeah? It has this as a reference voltage circuit (below) for a comparator to compare against a thermistor and pot combo. LM324 Odd taking a reference voltage from an input. Have never seen this circuit before. I think I have drawn it correctly. The op amp will drive the output to minimize the differences between pins 5&6 so pin 6 should reflect the voltage of the divider with lower impedance. Anyone see why this wouldn’t work? I was sure I had traced it incorrectly, but I think this really is the circuit. It seems the values of R10 and R11 are not critical. Or are they? <image[1].png> -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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