1 step forward 2 steps back with the electronics i3

Building my first i3 with the Ramps 1.4 and mega 2560. Just solved a stepper driver issue by swapping to a new mega 2560 (previous post). (no idea what the problem was). Anyway, had all motors working smoothly.

Then I went and plugged the extruder thermistor and heatbed thermistor in to the T0 and T1 spots on the Ramps board not realizing I had the 12V power supply plugged in at the time. To boot, I'm not sure if I mixed up the polarity on them. The first pin on T0 I plugged the negative and the next pin positive. Is this backwards? There was no zap or smoke or anything.

Anyway, quickly unplugged the power supply and the thermistors. I fired everything back up with just the LCD and the steppers plugged in and now nothing works:
1. Nothing on the LCD
2. No red light on Ramps board and reset switch does nothing
3. Tested the power terminals on Ramps and they are drawing 12.1V
4. Mega 2560 works when plugged into computer (i.e. proper lights flash when loading firmware) doesn't, however power the LCD through ramps like before
5. Pronterface suddenly doesn't recognize the board

All I have is a basic multimeter to test things. Can anyone tell me specifically what COULD be wrong on the ramps? How I would test it with my multimeter? or if it's already obvious that I screwed up my Ramps board and I need to buy a new one?

Any insight from the better informed is much appreciated. I was enjoying learning about the electronics, but after so many setbacks, I just want to get printing.

I've included a pic of my ramps board with a couple of arrows to the T0 and T1 pins.

thermistors dont have polarity...

remove all stepper drivers from the board (while off) and try again... if they have died they could be shorting out the board.

i guess that solves that then. Is it possible then that the plugging and unplugging of the thermistors while powered on would ruin something in the ramps board?

Quote
Dust
remove all stepper drivers from the board (while off) and try again... if they have died they could be shorting out the board.

So I unplugged everything from the ramps except the 12V power supply. It seems that the mega is getting power when plugged via usb, but nothing gets power through the ramps. I've tried it with both my mega 2560's and both get the same result. Is there a way for me to test with my basic multimeter to see if it's the regulator on the mega's? Or if the ramps itself is fried or something?

Thanks.

well power from the ramps to the mega is just threw the 5A fuse then threw D1 to the mega. very little to it.

Fist check power is getting threw the 5A fuse, multimeter on dc voltage, find the two pins between the power plug and the stepper socket labled 12v-aux

called extruder fan in this image


One probe on each pin. Should read 12v or -12v if probes are backwarads (which doesn’t matter in this case)
DO NOT SHORT THE PINS.

If that has power move on to the diode d1

located here


note the silver band.

test for voltage, put the negative probe to the negative pin on the power plug, put the positive probe to the dioide leg on the silver side. it should read near 12v

If they are both good. its an issue on your mega

Thanks for the detailed descriptions Dust! It looks like my 5A fuse is good, but the diode is reading 0. So do you think I should be able to just remove that diode and solder in a new one to solve the problem?

I replaced the D1 diode (n4004) and am getting 12V on the power terminal, 12V on the pins, but still getting 0V on the diode (see pic).

Any ideas on what the next thing for me to test might be?

Thanks again for the help!

ok, finally found out the problem with this. It was a tiny scratch on the bottom of one of the traces from the 4004 diode. Soldered a pc of wire to the trace and it's finally powering the arduino. One more problem to solve via a different post and hopefully I'll be printing!

cfry:

I had similar problems to what you describe and it took me what felt like ages to get the electronics stable. I went through a Ramps board, and Arduino, and a number of Stepper Drivers. The thing is, my problem resolution process was not scientific enough that I am sure what was really bad and what was a red herring! The good news is that once I got the electronics stable they have stayed so and I have done a lot of printing! The bad news is that you will likely have mechanical and extruder challenges next! All part of the reprap game me guesses.

Hang in there!

Wisar

P.s. Some day I will swap back in the bad components to see if they are really bad...just not for a while given that I am printing!

I did a similar thing, where my steppers were running really rough.
So while switching drivers around, I once plugged one in one pin off, and fried the power voltage thing on the mega that takes in current from ramps.
So I bought new mega and new drivers and it worked.
The rest of my prusa I3 is a dream, except the little extruder gear slips after several hours printing, because the pla softens from the motor heat.
I would recommend always buying ABS parts now, even if $20 more on ebay.
You need them anyway to allow heated build chamber.

I do feel that an aluminum small gear, t2 belt, and abs large extruder gear is worth it. Its quieter and aluminum gears do not warp so way more dependable.
I am thinking a strapping tape system might work too, just not impressed with the herringbone gears.