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Thermistor readings on Melzi 2.0 vs 1.5

Posted by Taerzik 
Thermistor readings on Melzi 2.0 vs 1.5
November 01, 2016 06:14PM
Preface:
Bought a Prusa i3 a few years ago, it had the phony Chinese knockoff of the Melzi 2.0 board.
After several years of learning and struggling with the issues of that board I went and replaced it with what seems to be an actual Melzi 2.0 board.
The old board had burnt out the switch to the hot bed immediately after it first started so no hot bed - I just disconnected it.
I also got the (no surprise here) 'suprise' when FTDI pulled that stunt with bricking the phony chips, got around it eventually.
That's the my main reason for the replacement - the hot bed.
Oh yeah, and the thermistor pullup resistors were 10,000 on that board.
On the old board, the thermistor on the hot end seemed to be fairly accurate.

As for the new board;
The RS232 seems to be legitimate - in fact it refused to talk to my hacked driver files.
The pullup resistors on the thermistors both say they are 47000.
So, as far as I can tell this board is the real deal.

I'm trying to get the new board installed now and I'm having trouble with the thermistor readings.
To make things easier on myself, I used my old Marling config that I had backed up in case I needed it but the thermistor readings have been problematic.

Issues:
1. Sometimes when the printer starts up and connects I get no reading from the thermistors, just 0 degrees.
2. Sometimes when the printer start up and connects I get a message saying that the printer has triggered an error about max temp. being too high on the hot bed and then no readings thereafter.
3. Sometimes when the printer connects it DOES give me readings - they seem to be consistently at or about 147.9, Celsius presumed.


Can someone shed some light on this?

Thanks!
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