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Support Forum » LCD won't turn on, chip + voltage regulator heat up!

September 01, 2010
by jafework
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Hi, I have been trying to get my kit to turn on but so far no go, it just heats up, I have started over from scratch 3 times now, and have checked all my connections against all diagrams and still no go, even used a multimeter to check all the voltages. Everything looks good, it just doesn't work see picture: alt image text

September 01, 2010
by hevans
(NerdKits Staff)

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Hi jafework,

Nothing immediately jumps out to me as being wrong with your wiring, but I'll keep hunting for something. The fact that the voltage regulator heats up definitely makes me think there is a short somewhere in the circuit. Were you able to get the congratulations message on the LCD at all? Try flipping the programming switch back to run mode (away from the chip) and resetting power to the chip. Do you get anything on the LCD at all? Also make sure that the contrast resistor is not shorting out against the 7805.

If you can, please take a slightly wider shot of your setup, so I can take a look at the connections to the LCD.

Humberto

September 02, 2010
by mongo
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It might help a little if the LCD was in the picture as well.

December 27, 2010
by isloera
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Same problem here. I got the congratulations message and also was able to load the initialload program with no problems, but today, when I was getting ready to load the temperature program the LCD did bot respond at all. I checked all the wires and looks fine. I used another brand new battery and nothing. The voltage regulator gets really hot I even burned my finger when I touched it.

December 27, 2010
by isloera
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Here are some pics

pic 1 pic 2 pic 3 pic 4

December 27, 2010
by mongo
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Well, everything looks like it should but it's kinda hard to tell in some spots. I just reposted this link for a construction hint. If you follow some of these examples, it makes troubleshooting much easier. Link

December 27, 2010
by mrobbins
(NerdKits Staff)

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Hi isloera,

If the only change was adding the temperature sensor chip, then please try removing that and see if that changes things.

Was anything else getting hot besides the voltage regulator, such as the temperature sensor chip or the microcontroller?

Also, from the photos, it looks like you might have a 10K resistor in place for the contrast resistor (brown-black-orange-gold) instead of a 1K (brown-black-red-gold). However, in that case, you probably wouldn't have received the LCD congratulations message yesterday, and this would not explain the hot voltage regulator.

Do you have a multimeter? Can you measure the voltage from the input to the voltage regulator to ground? And separately, measure its output to ground?

Finally, just a hunch: are you sure that the TO92-packaged item (the smaller 3-pin plastic chip standing up) really is the temperature sensor, labeled LM34? If instead you placed in one of the 2N7000 MOSFETs, then I think you'd have the symptoms you describe, because the MOSFET source would be connected to +5V and the drain would be connected to ground, leading to a huge current flowing through the MOSFET body diode.

Mike

December 27, 2010
by isloera
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I don't have a multimeter yet it will arrive on Wednesday ;-)

I tried removing what I was thinking was the temperature sensor chip and the LCD showed signs of life, but now it doesn't show the first half of the top two lines on the LCD.

You were right about your hunch, i used the MOSFET instead of the temperature sensor. I really hope I didn't damage the LCD with my mistake. I'm attaching a picture so you can see what it looks like.

Thank you both for your quick response

Alt Text

January 12, 2011
by dgikuljot
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From The Picture it seems like you have the contrast resistor connected to the output of the voltage regualtor.It is suppose to be connected to ground. Please just look into that.

April 09, 2012
by TY68
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I just bought a kit and could not get lcd on. I checked and checked... turns out it was a 10k instead for 1k. Those colors are had to see sometimes. I changed it and its up and going great! going to start on led array soon. these forums are very helpful. Thanks! Ty

April 09, 2012
by mongo
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It's been a while since I saw this one... That resistor also looks like it might be a 10k. (Brown, black, orange). If so, swap it with one with red instead of orange.

Also, double check the temp sensor connection. If the leads are in the wrong places, it can load down the regulator. This can also happen if you got one of the transistors mixed up with the temp sensor.

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