Heatbed on all the time. Does not cool down.
Our company just ordered an MK3S+ kit. Finished building it with little issue. The first time I fired it up, the only thing working was the green LED by the USB port and the red LED on the top of the SuperPINDA sensor. Pulled the fuses to check them and after putting them back in, the LCD display finally came to life, plus I had a red LED on the lower half of the board and an LED on the heatbed. Progress! Ran through the self test and everything checked out fine. However, shortly after, I got a MAXTEMP error for the bed. I noticed that the heatbed LED stays on all the time and the bed heats all the time even when the temp is set at zero. I double checked the polarity of the of the power cables. Black to GND, black w/ red stripe to VCC on the bed, and black on the left terminal, black with red stripe on the right terminal on the board. Thermistor is attached to the underside of the bed and connected to the correct spot on the board. Not sure what else to check. Any ideas on what is causing this?
Thanks.
RE:
I'm assuming that you've tried a power-off reset and the heatbed continues to heat, correct?
It could be that the FET on the Einsy Rambo which controls the heatbed (Q5) is shorted, or something in the logic on the gate of that FET is causing it to remain on. My guess would be the former, since IIRC, a fault will turn the heatbed off.
It could also be an unwanted ground on the line from the heatbed back to the Einsy.
If it's a new machine, I would contact support, and they will probably end up replacing the board.
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Cheerio,
RE: Heatbed on all the time. Does not cool down.
I've contacted customer support and have sent them pictures of the PSU and board as they've requested. Hopefully it's an easy fix.
In the meantime, yes I've tried a power-off reset and no change. Is there a way to test the FET on the Einsy Rambo to see if it is shorted?
RE: Heatbed on all the time. Does not cool down.
I've contacted customer support and have sent them pictures of the PSU and board as they've requested. Hopefully it's an easy fix.
In the meantime, yes I've tried a power-off reset and no change. Is there a way to test the FET on the Einsy Rambo to see if it is shorted?
The more I think about this, the first thing I would check and rule out is a short from the negative lead of the heatbed element to ground. If you are handy with a multimeter and electronic troubleshooting, this will be straightforward.
If the transistor on the Einsy is indeed shorted, it will most likely show up as a bidirectional hard short (close to 0 ohms) between the negative Bed-Out terminal on the screw terminal strip and ground. (Measured, of course, with the heatbed element disconnected.)
If this is the case (FET shorted) the best thing to do would be to replace the board, that is, unless you are VERY experienced and confident in doing surface-mount component-level replacement.
I keep a spare Einsy board in the Prusa crash kit. They are not cheap, you can get them for US $90-ish if you look around, but it's one thing I would rather have and not need than need and not have.
RE: Heatbed on all the time. Does not cool down.
I keep a spare Einsy board in the Prusa crash kit. They are not cheap, you can get them for US $90-ish if you look around, but it's one thing I would rather have and not need than need and not have.
One way to almost ensure you'll never need it.
RE: Heatbed on all the time. Does not cool down.
I wonder if there's some way to test the thermistor?
some way to test the thermistor?
With a multimeter: Read the resistance, warm the thermistor and watch for the value to change.
Cheerio,
SOLVED: Heatbed on all the time. Does not cool down.
So, finally got this sorted out. After multiple emails with Prusa tech support and them having us try different things, they finally sent a new EINSY board. It arrived yesterday, just got it installed and everything is working as it should. Just started my first practice print.