EXTU 1 SENSOR ERROR AND HEAT BED NOT HEATING

Nivas

I am currently working on an a5s printer. It was showing sensor error. After looking in the internet I found it was the thermistor that's faulty and I got it changed to a new one (100k 3590 NTC thermistor). after assembling it I still get the same error and the heat bed is not working. Can anyone lead me on how to sort this error and make the printer working? I tried using marlin firmware, but after uploading I get thermal runaway reset printer error. So I decided to upload the original a5s firmware and I'm still getting the same error. 

Samuel Pinches

Welcome @Nivas

If you've replaced the thermistor and still getting a sensor error, then either there is a broken connection or short circuit in the wiring, OR (and more likely) the motherboard is damaged on the thermistor port.

Take a multimeter and measure the resistance of the thermistor, measuring from the plug that goes into the motherboard. Should read around 100K ohms at 25C. That would confirm the thermistor and check the wiring at the same time. If that is all ok, then you need a new motherboard.

Out of curiosity, what temperature does the printer indicate for nozzle and hotend on my marlin firmware?

Nivas

Thank you @Samuel Pinches.

Really thankful for your guidance. I did the same as you mentioned above and I got around 83k ohms while measuring the resistance. I'm really confused a bit cuz the heater cartridge is also not heating. Even after turning the printer ON I still can hold it in bare hands.

 I really would want to know if that's supposed to happen even during sensor error or is it a faulty cartridge? Before changing the mother board I just wanna know if there's any solution for this cartridge problem. 

And about the Marlin firmware, I uploaded it and could not get any readings on the LCD screen. It was just showing EXTU error and that the printer need to be reset. So I uploaded the original a5s firmware. Now when selecting extrude option it shows temperature as 341 C. But when selecting heat option its the same sensor error being displayed.

Can I get some advice on how to sort this out? I would really like to see the printer work again and further I would like to upgrade the printer using Marlin. Kindly help me on this issue.
Thanks in advance.

Samuel Pinches

If there is a sensor error, the motherboard will not heat the cartridge for safety reasons!

The table below shows the relationship between thermistor resistance and temperature, for a typical 100k thermistor type (not exact -- every thermistor model will have a slightly different response). A resistance of 83K should correspond to ~28C, does that sound correct for the real world temperature?

If the motherboard is reading 340C, that typically indicates a short circuit in the wiring OR a damaged port. Since you checked the reading at the end of the wiring, you can eliminate the wiring as a possibility. Hence, the motherboard is damaged -- quite possibly the CPU analog input pin is fried.

Nivas

Thank you @Samuel Pinches for reaching out. As per your advice I'm assuming the main board is fried. Before I go for purchasing any parts, is there any other ways to make the printer working without a mainboard connection i.e. connecting the printer to an arduino mega and ramps board based setup using your Marlin firmware or is it just going with the stock version of the printer? If there are any setup that can be made using Marlin firmware that can run the printer without using the main board please do let me know. It sounds crazy but I really wanna dig about these kinds of setup... Thank you for spending time on this issue. Much appreciate it sir.

Samuel Pinches

You can by all means, replace the motherboard and LCD system with a different board. However, you will need to adapt many of the plugs and connectors, as well as find a new way to mount a different sized board with different positioned mounting points. For this reason, it is quite a lot easier to replace with the same proprietary OEM board. But up to you how far you want to go down the rabbit hole.... totally possible!

Nivas

Thank you @Samuel Pinches
I will try to change the board as of now for a newer one and make the printer work. Will keep posted about the progress on the forum. Much appreciate for your help.