1 Topic by andysteed

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Topic: Possible short circut

To preface this I know its my fault and I'm still very new to all this.

I broke my glass bed, so as I was installing a new Mk2b bed and as I was playing around it 2 wires touched (possibly the heatbed solder and the auto calibration wire)
Now the screen shows almost nothing when turned on, although the LED still works.
I'm not sure how to diagnose what exactly what i've broken.

As far as I can tell I might need a whole new board.

Any help would be great
Thanks again.

2 Reply by crocky

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Re: Possible short circut

Did you see my posts in the other message.

Have you got any voltage on the level wires (two blue ones)?

Both should have a voltage of about 3.3v to ground.

Does your board look like the one in the picture or is it different in the way the fuses are done?

The later boards use diodes as well.

Bob

3 Reply by andysteed

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Re: Possible short circut

I couldnt see anything wrong with the board.
I have to see if my dad has a volt meter to check
I think is the same as the one in the picture

4 Reply by andysteed

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Re: Possible short circut

I just had a look at the board again and it must be the other type of fuses, seeing as it looks different to this http://voltivo.com/forum/davinci-hwmods … ot-working

5 Reply by crocky

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Re: Possible short circut

Does it look like this?

This is where the wires meet up from the Power Supply Unit.

Connector 5V then GND
Connector 12V then 3.3V

To the right of the connections there are what looks to be a resistor and diode in three places, I would suspect one of those resistors is blown?

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Bob

6 Reply by andysteed

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Re: Possible short circut

I've looked closely at the 3 resistors and diodes to the right of the connectors and they all look just like yours.
Ill post a photo soon.
I'm not sure how to check if the voltage is 3.3V, we touched a volt meter with the end of the blue wire and the ground and got nothing. Were we doing it wrong?

7 Reply by andrewsteed

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Re: Possible short circut

I screwed up my login details so now i'm using this account...

8 Reply by ajwoot (edited by ajwoot 2014-10-24 04:48:21)

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Re: Possible short circut

I'm right there with you guys.  I installed a mk2b, wired it correctly and was able to print.  I stopped a print after a bad start to the first layer and pulled the extruder to the far right to clean it with a wire brush.  Being an IDIOT I started brushing the extruder nozzle and brushed right over my soldered connections to the heat bed.  After that mistake my display shows my Hot bed sitting at 149 when cold and when I turn on my extruder it will warm up but it will not display the correct heat.  My bed will not even activate because the machine thinks it's already 149 degree's.  I was hoping i could just replace a diode or resistor but i can't see anything on my motherboard that looks damaged.

9 Reply by crocky

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Re: Possible short circut

You haven't done any damage to the thermistor have you, it is the device that reads the heat bed temperature....

The 149 would make me look there first.

I'm just putting a standard heat bed back in mine, replaced under warranty because a wire disconnected itself.....

Bob

10 Reply by carl_m1968

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Re: Possible short circut

Sounds like you when your brush passed over the connections it shorted the heater power to the Thermistor. That in turn caused the thermistor to short. As a thermistor heats, it's resistance drops which cause a device to be able to read that as a temp change. If the thermistor is shorted then it will appear as a very low resistance and the device will see that as max temp. So you will need to see if you can source a new thermistor on that bed or replace the bed again.

Printing since 2009 and still love it!
Anycubic 4MAX best $225 ever invested.
Voxelabs Proxima SLA. 6 inch 2k Mono LCD.
Anycubic Predator, massive Delta machine. 450 x 370 print envelope.

11 Reply by ajwoot

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Re: Possible short circut

carl_m1968 wrote:

Sounds like you when your brush passed over the connections it shorted the heater power to the Thermistor. That in turn caused the thermistor to short. As a thermistor heats, it's resistance drops which cause a device to be able to read that as a temp change. If the thermistor is shorted then it will appear as a very low resistance and the device will see that as max temp. So you will need to see if you can source a new thermistor on that bed or replace the bed again.

Thanks for that I'll update as soon as the new hardware arrives.

12 Reply by imagecatcher

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Re: Possible short circut

I have changed the heat bed for a Pursa MK2b but kept the da vinci thermistor. I sandwiched it between the glass and the PCB heat bed. (left the plasctic hanging out at the back end) .I have done one lot of printing, no problem. Went to print today, turn it on and get error 0013 heat bed max temp...its cold - alson had the 0040 erro but a wiggle of the SD card seems to fix that. I am thinking I should have dremeled a recess in the pcb to house the microscopic thermistor as I think it probably cracked under the heat etc.
What is the thermistor specs for the heat bed? Hoping I can get one from Farnells / Element 14.
Anyone know?