RAMBo v1.2 and High Temp Readings

I was not aware that I needed to add anything to get that to work. I figured with the stock v6 thermistor it was a matter of just setting the proper type in the FW. The strange part is both the hotend and the heatbed are off by quite a bit.

Here is the schematic.

MacGyver: You are correct, you don't need to add anything. I was asking you to check that they didn't make a mistake on the board. The thermistor tables expect a 4.7k balancing restistor, IIRC - just as the schematic shows. Is the actual resistor on the board a 4.7k?

Also, is Vcc a steady 5v? Can you measure the voltage between TP20 and ground at a known temperature, say room temperature?

Carl - Read the first post. He already updated to the correct thermistor table.

Where'd you get the board from?

If I'm not mistaken, that resistor is part of the over voltage protection circuit.

If you shorted R73, I'd expect D12, the over voltage protection zener to immediately blow. I'd also expect you to not have over voltage protection anymore on your inputs.

Well I could be misunderstanding something. Was there a typo in your post? R73 is not 200k.

You said R73 is connected to AREF. Where is this on the schematic? I'm not seeing it on a quick glance.

My curiosity has been piqued. Can you link me to the schematic you were looking at?

If your fix works, you should be fine. There's no reason for there to ever be more than 5 volts on those pins unless there's user error, so the protection is a bit overkill (though good design!).

I just want to figure out why your fix works...because looking at the official RAMBO v1.2 schematic, I don't understand.

I've already filled out the RMA request, And it was approved for the return. I don't feel comfy about doing a mod to get the thermistor to work. Last thing I need right now is a fire at the homestead.

Should I get another RAMBo but from another manufacture? (Never heard of Geeetech) Or is there another controller I should look at? I really liked the idea of a software controlled microstepping and trimpot. Makes things easy and repeatable.

That whole path you described is unfiltered, unregulated +12v from bus 2. It can't be AREF or VCC, since 12v on those would blow the micro controller. I'm not seeing the label in the screenshots you showed?

As far as I can tell, AREF goes from pin 98 on the micro controller to C6, a bypass cap... and nowhere else.

Did you get confused between OVREF and AREF? They are different things - one is an over voltage reference, the other is the reference for the ADC.

I want to understand why shorting that resistor changed anything. Oh well.