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MKS sbase 1.3 - thermistor problems

Posted by automotives 
MKS sbase 1.3 - thermistor problems
August 21, 2017 11:28PM
Hallo everyone!

As this is my first post here, I do a little introduction to my self:

Introduction (you can skip this, not necessary for the topic itself):

I am Albert, mechanical engineer from Germany and I recently (march 2017) got into 3D-printing. In the meanwhile it is my new and absolute passion....
As I originally didn't want to neither spend the time on building a DIY-printer nor to spend the money for the originally desired Ultimatiker I went for a FlashForge Finder grinning smiley
I love that little machine, as the print quality and usability (HQ touch screen, WiFi, TMC2100 drivers) is quite awesome for a quite cheap plug&play printer.
So I got four more of them, as I thought: 3D printing is slow, I want my CAD-designs printed as fast as possible and there is some money left in comparison to an Ultimaker smiling bouncing smiley
It was a good choice smiling smiley

Nevertheless it has it's issues:
- building space is artificially restricted (140x140x140mm...)
- no heated bed

The lack of a heated bed was the biggest problem for me, as the room/garage where they are working is not heated and there were temperatures below 15°C at that time.
Bed adhesion and warping (even with PLA :/) were my enemies.

So a friend of mine suggested to take one of my finders and upgrade it to 32bit smoothieware, as there was a MKS sbase v1.3 in his possession he didn't use at that time.
The aims: Integrate a heated bed (214x214mm MK3cool smiley and switch to bowden / E3D V6.
Said and done, not a big issue. Among other modifications and some CAD designing this was realized without severe problems.
Building space is expanded to about 190x150x150mm (there is potential for more, especially in Y- and Z- directions) and meanwhile even dual extrusion is integrated in this "FlashForge Finder Plug&Play-Beginner printer".

32bit and smoothie are really nice and quick to master, but meanwhile I have temperature reading problems and the integrated stepper drivers are cruel in comparison to the TMC2100 of the FF Finder.
That's why I opened this thread.

MKS sbase 1.3 thermistor problems
I have four of these boards from different sources (chinese-shop, shops in UK and Netherlands).
At the beginning they worked great.
But after some time using them (abusing them? I had to connect and disconnect a lot and sometimes I forgot the 5V-USB power being still connected) , problems started to arise:

- one board is completely dead, no reaction to 12V or 5V (USB-) power - probably my fault... shouldn't be the topic here.
- board #2 and #3 have quite similar problems with temperature reading
- board #4 is new, no problems (yet)

Temperature / thermistor problems:

board #2:
Three of four thermistor connectors show temperatures of 929°C or 1044.2°C (switching) - doesn't matter if a thermistor is connected or not.
One of the connectors is still working like it should, so I use it to control a heated bed of one of the non-modified finders.
My skills and knowledge in electronics are quite low, so I can't explain for myself what is going wrong...
Screenshot of temperature readings:

board #3:
None of the thermistor connectors are working.
All of the thermistor connectors show temperatures of 202.3°C - doesn't matter if a thermistor is connected or not.
Screenshot of temperature readings:

My questions and I would be so thankful if there are answers to these:

(1) What can go wrong with temperature readings? What and how can this "break"? I don't want destroy more of those boards...
(2) Is there any possibility to repair this for myself? Hardware-like or software-like ("hard reset" or sth?)?

Thanks a lot to everyone!
Re: MKS sbase 1.3 - thermistor problems
August 22, 2017 04:13AM
Super high temperature readings like that indicate a short circuit on the thermistor input. Those inputs usually have an RC low pass filter and then go directly into the uC chip. Check the resistance across the thermistor input pins on the board. If you have a microscope you can inspect the uC pins on the board- it's possible that a solder ball is causing a short and can be eliminated by washing the board with IPA. Otherwise you're probably going to have to replace the uC. It's not too hard to do if you have a hot-air rework station, microscope, and some liquid flux.

I suspect this problem is caused by static discharge through careless handling of the board.

Edited 1 time(s). Last edit at 08/22/2017 04:14AM by the_digital_dentist.

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