Stop! 1st - that is a VERY good question - lots of detail - thank you.
2nd You need to do a little more troubleshooting b4 you jump to buying a new HE.
It is possible the HE is causing a power spike, but it is also possible there is a problem in the control board.
What happens if you disconnect the HE? Does the 3DP still restart?
If it does, you may need to replace your control board - or do some serious troubleshooting.
There are a couple of Heater ports on that RAMBo PCB. You could try the other port.
I think you would have to reconfigure your F/W to use the other port unless you have 2 HEs.
You can find the full schematic of a RAMBo 1.2g bd [link|https://reprap.org/mediawiki/images/thumb/9/91/Rambo1-2-schematic.png/1599px-Rambo1-2-schematic.png|here]. This is a typical heater driver
[image|3617136]
Only the heater drivers have the Zener in the 12V feed. You should check those.
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The MOSFET also has a reverse diode which might be bad. Not sure how to test that.
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But it is driving a resistor, so there shouldn't be any voltage spikes for it to suppress.
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Bottom line - my hotend (not a Prusa) uses a resistor that measures 3.55Ω for 112V supply.
Check that. It should be an easy replacement if it is bad. You don't replace the whole HE.
Stop! 1st - that is a VERY good question - lots of detail - thank you.
2nd You need to do a little more troubleshooting b4 you jump to buying a new HE.
It is possible the HE is causing a power spike, but it is also possible there is a problem in the control board.
What happens if you disconnect the HE? Does the 3DP still restart?
If it does, you may need to replace your control board - or do some serious troubleshooting.
There are a couple of Heater ports on that RAMBo PCB. You could try the other port.
I think you would have to reconfigure your F/W to use the other port unless you have 2 HEs.
You can find the full schematic of a RAMBo 1.2g bd [link|https://reprap.org/mediawiki/images/thumb/9/91/Rambo1-2-schematic.png/1599px-Rambo1-2-schematic.png|here]. This is a typical heater driver
[image|3617136]
Only the heater drivers have the Zener in the 12V feed. You should check those.
Bottom line - my hotend (not a Prusa) uses a resistor that measures 3.55Ω for 112V supply.
Check that. It should be an easy replacement if it is bad. You don't replace the whole HE.
Good luck.