I discovered that the 240 VAC line coupling cap only has about 25% of its rated value. Most of the voltage was getting dropped by that cap. So once I get the replacement part, then the whole circuit can get proper power and we will see what voltages we have at the different places in the circuit. I think I must have had a bad surge. Lost this water heater and the digital read out on my main manual lathe is totally goofy now too.
From: Chuck Macenski Sent: Tuesday, December 4, 2018 6:59 PM To: [email protected] Subject: Re: [AFMUG] OT Linear Circuit Did you look at REFf with a scope? Is that an oscillator? On Tue, Dec 4, 2018 at 3:44 PM <[email protected]> wrote: They also have a pair of LEDs in parallel with each other but in series with the op amp power rail to indicate output. Crazy all over the place. From: Mark Radabaugh Sent: Tuesday, December 4, 2018 2:29 PM To: AnimalFarm Microwave Users Group Subject: Re: [AFMUG] OT Linear Circuit Check the V- side of the circuit - is it tied to 0v or is that the output? https://www.edn.com/design/analog/4320338/Op-amp-can-source-or-sink-current version (e) looks a bit like what you have and they are using the negative rail of the chip as a constant current source. Mark On Dec 4, 2018, at 3:51 PM, [email protected] wrote: 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, <[email protected]> <[email protected]> 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 [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com ---------------------------------------------------------------------------- -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com ------------------------------------------------------------------------------ -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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