Heated Build Platform is dead

[Mount PrintMore]

I went out to run a print this morning and my HBP wont warm up at all.

I used S3D to command the bed to 100C, then did the following:
I unplugged the harness at the bed and measured the voltage with a meter and got 1.8 Volts.
I checked my supply voltages into the control box and they were 12V and 19V respectively.
I opened the control box and unplugged the connector with the HBP label on it from the board (the large one with screw terminals) and measured the voltage on the pins the board and got 1.8V.

This leads me to believe the problem is not in my external wiring or my HBP.

Upon visual inspection, I did not see any signs of "melting" or other physical damage to any of the components, but I wasn't 100% sure where all to look.

Where do i go from here?

[ednisley]

I unplugged the harness at the bed and measured the voltage with a meter and got 1.8 Volts.

Caution: unplugging widgetry with the power on can produce Very Bad Outcomes. In particular, unplugging a powered stepper will almost certainly kill its driver chip and scrap the entire RAMBo. The HBP isn't as inductive and has a more durable MOSFET, but the principle still applies.

The original M2 HBP connects between +12 V and the MOSFET. When the MOSFET is turned off, both HBP terminals float at +12 V. When the MOSFET is turned on, it pulls that wire to ground and draws current through the HBP from the power supply.

As a result, when you disconnect the HBP cable at the platrorm and measure the pin voltages with respect to ground, you'll see +12 V on the red wire (from the power supply) and a random voltage on the black wire: there's nothing supplying a voltage to the MOSFET.

The HBP cable typically breaks just outside the red connector, where the wire's insulation may hold the fragments together enough to confuse you: it shows continuity for low current (from your ohmmeter) and opens under high current (from the HBP). You can find that by measuring the resistance while flexing the cable: if the resistance isn't zero and constant, then you've found the problem.

Unfortunately, the wires bonded to the HBP heater may break at the edge of the heater pad on the bottom of the aluminum plate, which requires a new HBP. You can find that by measuring the heater resistance (with the cable unplugged) and flexing the wires: if the resistance isn't about 1 Ω and constant, then you've found the problem.

After you have it working again, you should stabilize the HBP cable to prevent stress concentrations at the connector and heater. I built an ungainly contraption that may suggest something better:

http://softsolder.com/2013/04/07/makerg ... orm-cable/
http://softsolder.com/2013/07/05/makerg ... ilization/

Good hunting!

[/quote]

[Mount PrintMore]

Thanks for the tips.
I pulled this back apart and measured resistances.

I am getting about 1.0 Ohm through the heater when I wiggle the cord around, it doesn't seem to be indicating a problem.

I'm measuring continuity through the wires out to the HBP connector from the connector that plugs into the circuit board out to the red Deans plug.
I'm getting about 0.01 ohms on both wires, again no matter how much I wiggle them.

[Dale Reed]

Turn off both supplies and wait a minute or two, then pull the power connectors at the back of the RAMBo and inspect the pins.

The "Phoenix" style connectors used for power, in my industrial experience, are better "signal" connectors than "power" connectors. A number of people have reported having the 12V supply connector work loose, reducing the area of contacts actually making contact (thus increasing the resistance) and causing the connector to overheat, corrode, and actually melt. So inspect the contacts and connectors, and if the connectors are at all deformed or the pins of the connectors not shiny, you'll need to replace the connectors.

Replacing the connector on the cable from the power supply is easy -- unscrew the terminals, get a new connector, re-strip and insert the wires (keeping close track of polarity), and screw down tightly. Replacing the connector on the RAMBo is another matter. Either replace the entire board (pricey), or, if you're good at de-soldering, remove the old connector and solder on a new one.

If you go to the bother of removing the connector from the RAMBo, I might suggest replacing it with a connector designed for power applications, such as Anderson PowerPole connectors. You won't find those as PC-mount connectors, though, and if you did, almost certainly the contact spacing would be different. Simply solder short pigtail wires to the board (14 AWG or larger if at all possible) and then put whatever kind of power connector you want on them.

Someone here on the forum simply soldered the power supply wires right into the board as an alternative, IIRC, but I like to be able to separate the power supply.

Anyway, turn it off and inspect those connectors!!!
Dale

[Mount PrintMore]

Yep, I unplugged the power supplies from the back of the Rambo and sure enough one of the connectors for the 12V supply is melted.

When I checked the voltages with a meter, I left them plugged in and just measured by touching the exposed screws on the terminal.

Thank you guys!
Mount PrintMore

[Mount PrintMore]

I've done a little searching, but am not having much luck finding a part number of what to order to replace the damaged connector. I found this discussion in the old google group:

https://groups.google.com/forum/#!topic ... gtdY8L3D7E

Does anyone have a part number handy?

I saw a similar discussion on the new forum where someone was trying to nail down the part numbers for the connectors used for the fans. It seems like it would be helpful to get a running thread going documenting part numbers for the various purchased finished pieces like all these little connectors.

[Mount PrintMore]

I received my new 2 pin connector for the 12 Volt supply.

I put it on in place of the melted connector and plugged it back into the machine.
I did a couple of other things to try to make this less likely to happen again:
1) I used conductive silver epoxy to essentially glue the wires into place inside the screw down connections. Obviously I tightened the screws quite tight as well.

2) I used a pair of zip ties to hold the wires into place by looping one around main harness trunk that runs right in front of these connections and then using the second tie to hold the power connection to that first zip tie. I did this for both connections. This way, if I move my machine a bit or something tugs on the power wire connections it pulls on the trunk harness as opposed to pulling the connectors out.

I've run about 6 prints for a total of about 10 hours of print time and it has melted again. It's the same pin that melted the last time.

So, I'm back to no heated bed.

Can something else be going on with this? My first connector ran for about a year with no problem and now it has failed and a replacement has failed in short order. I'm quite confident that the connection between the wire and the screw down terminal was good (due to the silver epoxy). This makes me suspect the actual male/female pin joint as the cause of the heat.

It seems like something else must be going on.

--------------update------------------
I took a closer look at the connector on the rambo board and I can see signs of damage to the connector on the RAMBO. Now this is a real problem....

[jimc]

yes when you have a melted connector you cannot just replace one half of it. its almost guaranteed to melt again. the connector on the rambo board should also be replaced. many people just remove the connector from the rambo and solder wires directly to the board just like dale said. there is nothing going on with your machine. the heated bed just runs right at the limit of the connector thats they use on the rambo board. the m2 was changed to 24v a while back to help eliminate this problem.