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Thermocouples, slow down lights, related CEL’s, and how to conquer them...

Discussion in '348/355' started by jevs, Aug 9, 2012.

  1. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #1 jevs, Aug 9, 2012
    Last edited: Aug 9, 2012
    I am starting this thread in response to my own car having slow down light issues after installing aftermarket exhaust components. This should also help people having troubles with thermocouples or thermocouple ECU’s on stock or other configurations of exhaust.

    I will be posting information I find while looking into this and learning more about the thermocouple system. It may also morph into a way to eliminate the thermocouples and thermocouples altogether and keep the computer happy.

    This will be focusing mainly on the 1996-1999 355’s with the 5.2 Motronic system. The 1995 models are not as picky and from what I understand may be easier to defeat the slow down light (I have not read much on the 2.7 because I do not have one). This info will also be good for many other cars that use the same Thermocouples and/or ECU’s. The part that makes this tougher on the 355’s is that you also have to contend with the by-pass valve thermocouple.

    If you would like to read what led me to this point, feel free to read this thread:
    http://ferrarichat.com/forum/showthread.php?t=377790

    For tonight I will be starting with this:

    I am going to first measure the supply voltage going into one of the Thermocouple ECU's. I expect that it will be at battery voltage 13.8 V or so (I will refer to this as 12V from now on if it is). It was hard to tell on the schematic where the supply was coming from once it hit certain module blocks with vague descriptions so I am just going to measure it for myself (faster than staring at schematics and I do not entirely trust the WS manua)l.

    I will then pull the module and a thermocouple from the car so I can just work with them on the bench. I will apply power and ground to the module and connect volt meters to the output lead. I will leave the thermocouple attached to the ECU. I will then attach the thermocouple to my adjustable soldering iron (goes up close to 900ºF).

    Then I can change the temp on the probe and monitor the output voltage right at my electronics bench where it is easy. I will even be able to dial in an exact temp and see what the output is for future possible simulation. I can then pull all three systems and make sure they work the same. This will tell me a lot as well as test my components to make sure they are all working right in the first place.

    I have a good idea how I can build a nice simple module to eliminate all this stuff once I figure out what the computer wants to see in all bypass states etc.

    So, I am off to the garage. I will post back when I have some more info.
     
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  3. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
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    #2 fatbillybob, Aug 9, 2012
    Last edited by a moderator: Sep 7, 2017
  4. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #3 jevs, Aug 9, 2012
    Last edited: Aug 9, 2012
    Are those the same thermocouples as the 355 that were used? If there is no difference in those and the 355 then that will be great info for this thread.

    It also explains why I am seeing .5V all the way up to about 350-400º so far...I have everything rigged up now. I am not sure if I am going to be able to generate enough heat with the soldering iron. The thermal transfer is not great and the mass of the thermocouple may cause me an issue in doing this. I am working on that now, but was seeing no response so far and was about to pull another ECU to make sure this one was ok, but now I see there is no reason for concern yet.

    I have a feeling at idle and fully warmed up that my car is not even going to be bouncing the thermocouple ECU's output above that .5V since I was measureing 425º or so on the outside of the pipe. Of course with the closed bypass valve at idle, that one will also be sitting on the bottom rail at .5V at idle.

    Right now I am staying focused on testing the components to make sure they work on the bench, then I will get them all back in the car and start taking some measurments with it running.

    I will also post pics and instruction how to test that power and ground are good at the connectors in the car etc. just to make it easy for people visually.

    At least at that point I will know I am not chasing a bad part and move forward.

    Just to have all the info in this thread without having to refer to the WS manual....:

    If the slow down light is flashing then the catalytic converter temperature is too high reaching a level of 1724 +/-68ºF
    If the slow down light is constantly on then the catalytic converter has reached a level of 1796 +/-68ºF
    If the temperature reaches 1868 +/-68ºF for more than have a second, the ECU steps in to cut off the power supply to the injectors

    This is the info from the 355 Workshop Manual. I believe the values in the graph above were actual temp measurments when those components tripped the light?
     
  5. cavlino

    cavlino Formula 3

    Mar 6, 2002
    1,475
    Ottawa, Canada
    Full Name:
    Carm Scaffidi
    Eager to hear more :)
     
  6. Extreme

    Extreme F1 Rookie

    May 26, 2010
    2,515
    Northern Utah
    Full Name:
    Erick
    I’m interested in seeing what you learn.

    I currently have my thermomathingy not plugged into the exhaust after the bypass valve and I haven't noticed anything different. Is its only purpose to detect higher than normal temps like in the case of a stuck open bypass valve?
    The capristo I have has a bung for it however it's on the wrong side of the pipe and the thermomathingy wire isn't long enough to reach that side. That’s the reason it’s not installed.
     
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  8. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #6 jevs, Aug 9, 2012
    Last edited by a moderator: Sep 7, 2017
    OK, to help people out that are not in electronics for a living I am going to post up some very basic checks you need to do with pictures etc. This will be no brainer stuff for electronics guys so skip ahead the next few posts could get boring for you :)

    First of all locate one of your Thermocouple ECU's that you want to test. I chose the main right converter thermocouple because it is the easiest to access without taking anything apart. You can reach it above the lower right diffuser by just jacking ther rear up a bit.

    These instructions will apply to any of the three thermocouple setups (bypass, main right, main left).

    Do not have the key in the ignition or on at this time in case you hook something up wrong you will be less likely to damage anything.

    Next, pull the 4 pin connector loose (only 3 pins are used).

    The first thing you want to do is verify that you have a good ground right at this connector so you can eliminate a resistive or open ground as a problem. Keep in mind if your issue is intermittent or seems to happen with vibration of the car, it could still be a ground and you just happen to be checking it when it has a good connection. If this applies to you, then maybe shake or tap on things in the car to see if the connection ever goes to a higher resistance in response. If it does, you need to look for a an intermittent ground. Have fun with that. Intermittent problems that are hard to replicate are the worst.

    At this point, you want to attach one lead of your meter to the connector pin shown in the pictures below labeled GND (ground).

    Connect the other lead to the ground strap going to your transmission, or another known good chassis ground.

    Set your meter to ohms as shown. Now if you have something less than 1 ohm, and do not suspect an intermittent problem, then you are done testing ground. You have a good one :)
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  9. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #7 jevs, Aug 9, 2012
    Last edited by a moderator: Sep 7, 2017
    The next step is to verify that you are getting a good supply voltage to the thermocouple ECU.

    Switch your meter to Volts DC (Direct Current).

    Connect the black lead to the pin marked GND as shown in the picture.

    By the way I use straightened paperclips for this stuff.

    Connect the red lead to the pin labeled +12V

    Now at this point you should still have your key out of the ignition.

    Make damn sure that you do not let those paperclips or whatever your using touch each other. You will blow a fuse once you turn the key on.

    So, if your sure your leads wont touch each other, go ahead and turn the key to the run position, but do not start the car. You could start the car, but there is no need. The circuit will be energized.

    Now if you got anything greater than 12 volts here, you are good. If you were to start the car you may see this go up a little since the charging circuit will kick in. Again, no need to start the car (I hope you have a good working battery in your car already).

    So, you got a good ground and good power....that was the easy part :)

    I am going to skip checking the signal line at this time because you would have to find the connection point at the motronic to check this. You would simply ohm it from the signal pin of the connector over to the connector of the motronic and ensure it is not open and under 1 ohm. if you do need to check this, then make sure the battery is disconnected from the car (everything off). You don't want to risk damaging anything when you go probing at the computer and I have not done that to give you instructions.
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  10. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #8 jevs, Aug 9, 2012
    Last edited by a moderator: Sep 7, 2017
    Now that those are good, you need to remove the thermocouple and ECU if you want to test the way I did. You can splice in and check this stuff in the car, but to me this is easier.

    Turn the key off and take it out before you remove the parts. You won't need the car for the next steps. This testing will be done on the bench somewhere.

    Label the pins of your ECU as I have done with a sharpe or in some way that you always have the pins identified so you don't have an accident. There is risk of damage to the ECU if you short things together with power applied or apply power backwards or to wrong pins etc.

    Now you need to have some way of connecting leads to the pins of the connector on the thermocouple ECU. I had some connectors for some similar mating plugs that I crimped to some stripped wires and then put some heat shrink over. If you have an old connector on a junk harness or anything you can pop the pins out with the wires or something else. You can also buy some little clips or other things maybe at Radio shack that you can use. I will leave this to your imagination.

    I will be using a red wire for +12V, a black wire for GND, and Blue wire for signal.

    MAKE SURE THEY CANNOT SHORT TOGETHER. Take extra care or you may blow up a still good ECU.

    Go ahead and connector your leads or whatever you have devised. Leave the thermocouple attached.

    Keep in mind if going further something does not act right you may have to swap thermocouples and ECU's until you figure out which ECU's and thermocouples are good. I am going to show you how a good set should react.
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  11. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #9 jevs, Aug 9, 2012
    Last edited by a moderator: Sep 7, 2017
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  13. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #10 jevs, Aug 9, 2012
    Last edited by a moderator: Sep 7, 2017
    Now you will need a 12V power source. You can use an actual power supply, a car battery, an ATV battery, an alarm system back up battery, the battery out of your kids power wheel, the 12V battery out of your power drill, or whatever gives a good 12V DC power source. Make sure you know what negative and positve are on whatever you use as your power source and that it is good. I do not recommend that you use your car battery charger, or other charger. Most of these send out a nasty looking voltage that is stabilized by the battery itself when your charging it.

    Using a 12V battery is your best bet if you do not have a good power supply. Please use a low amperage fuse or something inline so it will blow if there is a problem. I recommend a 5 amp or less fuse. My power supply has short circuit protection, your battery will not!

    You now want to connect the positive output of your battery or power supply to the red wire or the +12V input of the Thermocouple ECU.

    If your using something with a switch, leave it off until you have everything connected. If your using a battery I recommend wiring in a switch or using the fuse that you were supposed to install as a switch. Be extra careful. A battery is live as soon as you start working with these wires and you can damage something if you touch stuff together.

    Next, connect the negative GND from your power supply to the black wire GND of the thermocouple ECU.

    Next you want to connect your multimeter. Make sure it is set to volts DC.

    Connect the black lead of the meter to the same spot as the black wire of the power supply on the GND wire of the Thermocouple ECU.

    Connect the red lead of the meter to the same spot as the red wire +12V of the power supply on the +12V wire of the Thermocouple ECU

    Make sure nothing is touching and go ahead and turn on your power source.

    You should now be reading 12 Volts on your meter. You are basically just reading across the power and ground to the thermocouple ECU ensuring that it is recieving power.

    The ECU is on at this point so be careful. Don't let the blue signal wire touch anything. If you see anything happening, smelling funny, getting hot, the fuse blew, your power supply shut off, or don't see 12V on your meter...disconnect your power source, you got a problem. Recheck your supply and make sure it is good. If the ECU is smelling funny or getting hot and you have connected everything correctly, then the ECU is bad.

    If everything looks good, continue on, your getting closer and you still have a chance that your parts are good :)

    I added a pic of my electronics bench for fun. If your going to do this kind of stuff I highly recommend have a little setup in the basement like this. It comes in handy all the time and you get to start saving money fixing your own stuff.

    Also, sorry for the spaghetti mess of wires in the picture. Don't let it scare you, I just have long leads on everything.
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  14. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #11 jevs, Aug 9, 2012
    Last edited by a moderator: Sep 7, 2017
    We are getting close to the fun part.

    At this point you can go ahead and shut off your power source unless your comfortable moving the red postive lead of the meter over to the blue wire.

    You need to move the red positive lead of the multimeter over to the blue signal wire of the thermcouple ECU.

    Leave the mutimeter black lead as it is connected to GND.

    Turn your supply back on if you turned it off.

    You should now be seeing about .5 Volts on your meter.

    If you do, that is a good sign. Your thermocouple is reading ambient air temps most likely. As you can see up above in the graph that was posted, the thermocouple stays at this level until up around 500º.
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  15. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #12 jevs, Aug 10, 2012
    Last edited by a moderator: Sep 7, 2017
    Now after all that you finally get to test the actual reaction to temperature! The soldering iron idea did not work out well. I decided to use a heat gun instead. So, now you need a heat gun. If you want to try an alternate heating method, your on your own.

    I found out my temperature reading device only goes to about 500º then says "HI". So, I was only able to see that the output voltage started moving up in this temperature range. Based on the graph posted above my thermocouple and ECU appear to be working correctly and if yours work this way, then they are good also......I see no need to graph anything since it was already done for us and we know the specs from the manual when we go to trying to invent a circuit to eliminate these parts we are testing.. :)

    So, go ahead and stick your thermocouple in the heat gun. Get it as close to the coil as you can, but don't let it touch! You may have to bend the heat shroud to get an opening big enough to fit the probe.

    Now the fun part. Turn on the heat gun. Use the highest setting.

    P.S. The first picture below is after the voltage started rising, so at the .6V it was probobly at about 600º. The other pictures are just to show points as it was rising to the last picture of

    P.S. the first picture below is after it started rising, so it was up to about º according to the graph above at this point.
    You should see almost no change from the .5V until it reaches around 500º. Again refer to the graph. Once you get past that, you should see the voltage climbing as the probe gets hotter. My heat gun maxed out its ability when the output from the ECU got to 1.341 Volts. Now the neat part is I can look at the graph above and know my heat gun was putting off about 800º.

    Next you can shut off the heat gun and watch the voltage fall back to .5 as the probe cools off.

    If everything worked out, then you got some good parts.

    Of course there is always some chance that something is out of tolerance in the ECU or thermocouple that could throw the voltage off a bit, but you will know this when you check your other 2. If they don't give about the same voltage output or peak out around the same, then you shuld be able to tell which parts are a problem.

    If you got this far, it is pretty unlikely your thermcouple itself is out of tolerance or bad. From what I have read they generally fail miserably or are good.

    Hope this helps you guys. I will be testing my other two thermocouples and ECU's when I get some more time. If they all check out, then I will make a decision of how to move forward since the slow down light problem will still be an issue and not solved by a parts replacement.

    P.S. The first picture is after the output was already rising (about 600º according to the graph above). The last picture is where it peaked out and my heat gun could no longer get it any hotter. So, the pics just show incrementing snapshots as it was climbing.
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  16. cavlino

    cavlino Formula 3

    Mar 6, 2002
    1,475
    Ottawa, Canada
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    This is terrific Jevs! Thanks for sharing the details. I see your ECU has the Green cover on it, those ones are supposed to be the better ones.
     
  17. Markphd

    Markphd Formula Junior

    Mar 10, 2012
    713
    Nicely done.
     
  18. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #15 jevs, Aug 10, 2012
    Last edited by a moderator: Sep 7, 2017
    Well, on my nice long 50 mile commute home from work today I was thinking of ways to test your signal wire back to the computer just in case someone messed up your wires during a major or something got shorted, or the Motronic computer input circuitry was messed up.

    So here is a a simple check you can do. Make sure the key is off at least and I recommend to go ahead and disconnect the battery at the shut off just in case so there is no power on the Motronic. I tested it both ways, but It is still better to go ahead and disconnect the battery.

    Now hook your negative black lead from your multimeter to the GND pin.

    Hook the red lead to the signal pin.

    Set the multimeter to Ohms.

    You should see around 312K Ohms (this is 312,000 Ohms). If you do, then your car wiring and the computers input circuit are probobly ok. I verified this on two of the circuits to make sure my car was consistant.

    Possible problems:
    1) If it is reading shorted (less than 1 Ohm, then you know your wire is shorted to ground somewhere.
    2) If you see something strange that is no where near the 312K Ohms, then you may have wires shorted together in the harness, or you may have a computer problem. To test if it is the computer, you would then need to disconnect the computer and check that pin right on the computer to ground and see if you get something close then. If you do, then it is in the wiring.
    3) If you see an open condition and are getting no resistance, then you have an open wire between the connector and the computer.

    Next picture will be of my pile of parts I picked up at the electronics store :) I have the circuits basically figured out to make safe, stable, adjustable bypass circuits for this (including one that changes when the bypass valve is activated to simulate the temp change). Keep in mind it will be beta, no guarantees on it working yet, but the theory is fairly good and I ran it by several people for opinions.
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  19. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
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    Suuweet thread.
     
  20. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #17 jevs, Aug 11, 2012
    Last edited by a moderator: Sep 7, 2017
    Since my thermocouples and ECU's are good. I decided they are never going to like my exhaust. I went ahead and bought all the parts I needed to make circuits to eliminate them. Total cost $27. I already had wire and a mating connector.

    I devised a simple circuit that has some protection and stability built in. See the attached schematic. A simple voltage divider could probobly do the trick, but I wanted some safety and stability. A simple two resistor voltage divider would allow your signal voltage to move around with battery voltage.

    This circuit uses a 5 volt regulator and then a voltage divider on the output. This way, the 5 volt regulator will always output 5 volts even if the cars voltage fluctuates. This will keep the output signal from the voltage divider (potentiometer) stable and right at what you dial it in to.

    The diodes are for protection purposes. The capacitors are to keep the regulator from oscillating and recommended by the manufacturers.

    IC1 = 78L05 5 Volt Regulator .100 mA
    C1 = .33 uF
    C2 = .33 uF
    D1 = 1N4001
    D2 = 1N4001
    R1 = 200 Ohm Potentiometer
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  21. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #18 jevs, Aug 11, 2012
    Last edited by a moderator: Sep 7, 2017
    Here is the built circuit. It is very simple to make. I am using automotive grade wire for power, ground, and signal wires. If you build this, make sure you do as well so it doesn't melt or degrade. I have a lot of wire left over from Painless wiring harnesses, so I used that.

    You can also see in the pictures where I went ahead and dialed the output to 1.5 Volts. Since this was tested to work for other people on other Ferraris and fell into a good range on the chart above, this is what I am starting with.
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  22. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #19 jevs, Aug 11, 2012
    Last edited by a moderator: Sep 7, 2017
  23. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #20 jevs, Aug 11, 2012
    Last edited by a moderator: Sep 7, 2017
    Now, lucky for me I found a connector that will mate to the factory connector with just a little modification. I have several connector kits from Casper Electronics. I do not have the part numbers for the individual parts, but I am sure you can call Casper Electronics and just buy these parts, or the whole Metripack kit PN 103009. This is just a 4 pin connector from that kit and all the connectors are the same, just different number of pins.

    Here is a link:
    http://www.casperselectronics.com/store2/product_info.php?cPath=63_56&products_id=686

    The only thing to modify is removing the tab as show.
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  24. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #21 jevs, Aug 11, 2012
    Last edited by a moderator: Sep 7, 2017
    Next , slide the little seals on your wires and strip them about 3/16" or so.

    Then crimp the connectors on. Make sure you have the correct crimper. You can buy a nice crimper that has removable tooling to change between crimps. I highly recommend this. Don't try to use a crimper that is not made for these.

    Then slide the pins into the connector housing.

    Next slide the rubber seals down into the housing.

    You will have to seal the 4th hole. For now I just stuck another seak down the hole. They do make plugs for these, but I will come back and seal it after testing everything in the car.

    Now you can put the back piece on that holds the seals in place.

    I screwed the boxes shut so I could do a test run in the car. Of course I set both boxes to output 1.5 Volts.

    After testing I will seal the boxes and put a strain relief zip tie on the wires in the inside. I will also secure each component with a dab of silicone and a couple dabs here and there to keep the board from bouncing around in the case. I will do this when everything is finalized.
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  25. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #22 jevs, Aug 11, 2012
    Last edited by a moderator: Sep 7, 2017
    The other thing about the connector I am using is that the lock tab is in a position that does not lock the two connectors together tight enough. You will have to use a zip tie or other method to keep them fully seated to each other. The rubber water seal and the connections inside are just right though.

    Here is a picture of my temporary zip tie job. I will use some high temp ones on final install.
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  26. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    Now I got some good news. I wanted to test my two new boxes and see what happens before I built one for the bypass.

    I left the bypass thermocouple ECU installed and just zip tied the thermocouple so it was reading the wind. I installed my two boxes followed by erasing the computers stored codes from last time.

    I then drove the car all over with mixed driving in town and on the highway. I opened the car up a bunch of times and even got it too fast to post about here :)

    Guess what! 30 miles of driving and no slow down light or pending codes. I hooked the computer up and had absolutly nothing (clean diagnostics). Apparently the computer does not care if the bypass thermocouple signal just sits there at .5 Volts reading the wind as long as it is seeing the 1.5 Volts on the main cat thermocouple ECU inputs.

    This is good news because I will not have to make a 3rd special circuit that changes voltage for the bypass.

    I will be removing the Bypass thermocouple and ECU though. I don't like sensors zip tied up in the car. It looks kinda hokey if anyone ever looks at it or I sell the car.

    I have to make a decision on what to do next. I can either modify my right main thermocuple box to also have a second connector coming out that feeds .5 Volts to the bypass thermocouple circuit, or I can make a 3rd box and just set the voltage to .5V.

    I will let you guys know on that. I am done for today....
     
  27. cavlino

    cavlino Formula 3

    Mar 6, 2002
    1,475
    Ottawa, Canada
    Full Name:
    Carm Scaffidi
    Awesome Jevs! And now there are three of us Oz, myself and you that have confirmed that as long as the ByPass thermo is connected to the ECU it doesn't matter if its just reading in the wind. It won't throw a code. Be prepared for some folks to ask you to make them some circuits :)
     
  28. jevs

    jevs Formula Junior

    Oct 13, 2010
    477
    Missouri
    #25 jevs, Aug 12, 2012
    Last edited by a moderator: Sep 7, 2017
    I cannot edit the above posts, but if you look at the back of the circuit boards I accidentally shorted D2 out of the circuit :) It will still work fine, but that was not my intention. That diode is there for protection purposes. I did correct this, so here is an updated picture. Sorry. I marked the spot that should have been left open with a white circle.
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