Hello,
I'm trying to build a midi-thru device, and I think I might have fried it somewhere while testing the power. Being my first project, I'm not sure if this means everything is useless, if there's only one part I need to fix, or if (optimistically) I didn't actually damage anything, and I am just measuring voltage wrong.
Also being my first project, bear in mind that you might see several glaring mistakes in my explanation.
This is the item that I am building (links to Ebay). Having soldered my guitar before, perhaps I was overconfident going into this, but I made sure to know how to read schematics, get the polarity correct, and (to illustrate how thorough I tried to be) even though resistors aren't polarized, I made sure that the resistors went in the same direction as the photo.
Checked to make sure that the solder didn't touch at any points on the bottom, and left out the ic's when checking the voltage with a multimeter, as per instructions.
The instructions suggested to plug in and check between pins 8 and 5 on the first ic socket. The adapter that I used was the 1 spot 9V adapter, as the instructions say "To be used with a standard wall adapter 6-12V". I plugged it in, set the meter to 20 on DCV (Not sure if that was the correct setting to use), and got a reading of 0.00. Also, I began hearing a strange phasing sound in the adapter, so I immediately unplugged it.
I dug through my random adapters and found a DC 7.5V adapter and plugged it in. Here's the thing. I am not certain if I did or did not see one of the LEDs light up briefly, or if I imagined it, but I know that that's usually a bad thing. I checked the 7.5V adapter, and noticed that the polarity was different than the 1 Spot.
So if I didn't screw up somewhere along the way to plugging it in, I think I screwed up when I plugged one of the two adapters in.
Either way, how would I go about checking to see where things went wrong? Please feel free to just link me to a good electronics bible if that's the scope of my next step. Thanks in advance for your help.
You're correct. Shortly after posting this question, I discovered that I had absolutely reversed polarities, and then found a page about the 7805 which said very clearly "Reversing polarity will immediately short the 7805." Optimistically, I now know never to reverse polarities again.
Good to know this.
But unfortunately, 7805 creates dead short sometimes. The problem is - across the 7805 multiple things are connected. Make sure those ICs are ok and also do not apply power directly before replacing the 7805. Because, if they are rated for 5V, even if you provide proper polarity voltage, due to the short, those ICs will get more than the rated voltage directly from the adapter. So be careful.
Sourav Gupta
PermalinkSeems like you put adapter in wrong polarity and fired the 7805 or other ICs. To rest assure, put a correct polarity power supply and check the voltage across the 7805 Ic. Any power supply with 8-12V rating will work. The 7805 will have three pins and you need to check the first one and the last one. If you could share the top and bottom image of the board, I could assist you how to check the volatge on those respective pins. This is the first thing you should try.
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Joined February 12, 2018 696Monday at 02:11 PM