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Wrong hotbed temprature

Posted by dolfin

dolfin

Wrong hotbed temprature
June 07, 2015 03:20AM

Registered: 8 years ago
Posts: 2

Hi,

I assembled a Prusa i3 printer (specifically the Aurora Z605) a few weeks ago, and it worked quite well.

This morning i connected to my printer and noticed that the hotbed temperature reading is 247 celsius degrees in room temperature.
When I heated the bed the temperature dropped to 238 celsius degrees...

Does anyone knows what the problem might be?

Thanks!

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o_lampe

Re: Wrong hotbed temprature
June 07, 2015 03:36AM

Registered: 8 years ago
Posts: 5,232

A shortcut between the thermistor wires .
Check the cable under the heated bed. Loose strands on the RAMPS-connector can also cause shortcuts.
When you unplug the thermistor and it still reads 238°C instead of 0°C, it is a shortcut on the board.
-Olaf

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dolfin

Re: Wrong hotbed temprature
June 08, 2015 06:50AM

Registered: 8 years ago
Posts: 2

I disconnected the sensor from the board, and it still shows that value.
I guess the problem is in the board.

Any idea how can I fix it?

Thanks!

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Salim

Re: Wrong hotbed temprature
July 22, 2015 06:43PM

Registered: 8 years ago
Posts: 8

I have the same problem here.

replaced the heatbed, problem remains
everything is working fine except the heatbed temp.

think the problem from the board.

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tadawson

Re: Wrong hotbed temprature
July 22, 2015 10:28PM

Registered: 9 years ago
Posts: 606

There are basically three parts involved . . . The sensor, a pullup resistor, and the A to D converter in the Arduino. Since RAMPS has three thermistor inputs, and we use two, you can always move to the unused input, modify pins.h, and call it good . . .

- Tim

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Salim

Re: Wrong hotbed temprature
July 23, 2015 09:45AM

Registered: 8 years ago
Posts: 8

this is a melzi board, everything is working fine except the heatbed temp?
any suggestion where I should inspect in the board ?

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mel0n

Re: Wrong hotbed temprature
July 24, 2015 03:08PM

Registered: 8 years ago
Posts: 135

Either a short circuit somewhere, or incorrect thermistor table, or A2D conversion. I would say your board is suspect if you haven't changed your firmware lately. You can always use a multimeter on the ends of the thermistor wires where they connect to your board (not attached to the board) to check the resistance and make sure your board really is the problem.

My creations/2020 aluminum parts/FolgerTech i3 upgrades [www.thingiverse.com]

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Salim

Re: Wrong hotbed temprature
July 27, 2015 07:14PM

Registered: 8 years ago
Posts: 8

Hi mel0n

I have my brother electornics engeneer who checked the boards (another working one too) components compared values and said it should be an A2D conversion.
could firmware upgrade fix this issue ?