Solved Another Print Bed Not Heating Thread

I don't know why it's not heating but the D8 LED does not light up when I tell the bed to heat itself, which according to this thread: http://forums.robo3dprinter.com/index.php?threads/bed-not-heating.4446/#post-39232 means that I am not getting 12V to my bed from the board. Where do I go from here?

My bed reads 21C at room temperature. If I put my finger on it for a few minutes it goes to 22C, then 23C so the thermistor is working. I've also unplugged and replugged just about everything I can think. The bed does not heat it self at all.

Recently I had to remove the bed because a print was so stuck to it that I had to use a small chisel and hammer to remove it... However the bed was fine after that for 2 prints, it's just now stopped heating. I don't think this caused my issues but I thought I'd mention it just in case.

Thanks for your help.

 

Have you tried heating the extruder? If the print head thermistor is shorted, it will throw an error "min temp" and not try to heat. Can't remember if it also causes the bed to show 0 temp though.

 

I've done several PLA prints with the broken bed, the hot end is fine.

I tried everything for the stuck print, heating, cooling, taps from a hammer, I even iced the print with the bed hot. It was crazy.

I'm about as bad with electronics as you can be so I'm going to ask a few more questions. There's no DIY on this so I may need to be walked through this:

1. I have a multimeter but never used it. When testing wire connectivity do I turn the Robo off and set the meter to Ohms and then what?

2. Assuming my wires are fine, how do I check the D8/Q3. I would think the robo needs to be on?

3. Can I buy any RAMPS board that comes up on google?

Sorry for all the questions. I'm a mechanic kinda guy, nuts, bolts, fuel, fire, and grit. There's two things I don't do well, electronics and fireworks because something always goes wrong... Hopefully this will be simple

 

The robo doesn't need to be off or on to measure continuity. Measure the resistance across D8. It should be around 1.4 ohms. This will tell you if there's an open circuit.

With the robo on measure the voltage coming into the 11A side of the power connector. Should be 12v.

If you're measuring 12v coming in and the bed reports ~1.4ohms of resistance then it's isolating the problem to the polyfuse and mosfet.

There's some testing we can do further to see if the mosfet has failed but we'll cross that bridge after we isolate the problem.

 

Ok, reporting back.

1. I did not short anything That's a first for me, btw

2. I am reading about 1.6 Ohms across D8. I also unplugged the bed and got the same reading, so it looks like my bed is fine.

3. I get NO voltage across 11A. There is about 24-26 volts coming into the power connector across from it, but nothing coming out of 11A. I checked 5A below it just to make sure I was doing things right and it reads 24-26 volts, which means I have a power supply problem.

What do I do now? (Thanks for all the help by the way)
I have a soldering iron and supplies. Is this just as simple as removing the power connector and restoring connectivity to 11A?

 

24-26v?! That's not good.

You need to disconnect the power connector and figure out what's going on. Follow it back to the power supply

 

I had my multimeter set to ACV following an online tutorial I found. Maybe I should try DCV? (did I do something wrong already...)

I also wanted to note, the bed stopped heating right after I installed a new shroud for my extruder cooling fan. I thought it was just coincidence but it looks like I had wired the fan (previously) into the power connectors across from 11A for a steady power supply. Could this be my problem?

 

It's DC yes.

Sounds like a coincidence but I would have no way of knowing. The circuits aren't connected unless you shorted a fan wire and it's connected into the 11A side of the connector.

 

Well, you're not going to believe this.

My bed works again.

I just went back to measure it with in DCV mode, turned it on and D8 was lit up. The bed heated up and everything. But then as I went to screw the board back on the light went out.

I'm thinking I have a loose connection with the power connector. Depending on how I push on the incoming wires D8 will light up or go off. I have tried unplugging them and reinserting them but when I go to put the board back D8 still shuts off.

How can I trouble shoot this? Should I look into the connector? I know I am getting power to the connector and my fan wires, which are just wrapped around the power supply wires, are running my fan no problem. Can I open the connector up?

 

The connector will pop off allowing you to more easily work on it. Sounds like it's just a loose connector.

If you remove the wires from the connector then tin the ends with solder that should make for a more reliable connection. Soldering the fan wires to this wire doesn't hurt anything either.

You might be screwing down the board too hard as well.

 

I'm talking the light goes out as soon as the board is in position to be screwed in.

I'll pull the connector then. The power wires already have solder on them but maybe I can just heat that solder back up and reposition it on the wires.

Thanks again

 

Remove the ramps from the arduino and look for any loose pins underneath.

 

So I pulled the connector and the positive power prong is fried. Or at least corroded, kinda hard to tell. Check out my pic.

 

Submit a replacement part request for a new ramps. While you wait for them I suggest buying a new connector and replacing it yourself.
http://www.digikey.ca/product-search/en?lang=en&site=CA&KeyWords=WM7847-ND