Hot end won't turn off

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VAXHeadroom
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Hot end won't turn off

Postby VAXHeadroom » Fri Mar 16, 2018 6:31 pm

I guess I've fried something, but my hot end control won't every turn off. Even after cycling the main power, I measure 12.3VDC at the Rambo board.

How did I manage that?
Well...
I was changing out the heating resistors for heat cans, and ended up with 2 heat cans that measure 4.2ohms. So instead of wiring them in parallel (the older resistors measured 8.4ohms each) I wired them in series resulting in 7.1ohms. OK - bad idea on my end, but now have I toasted drive circuit on the Rambo? And since I now had a HIGHER resistance than before why would that have occurred?
Any help appreciated.

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geneb
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Re: Hot end won't turn off

Postby geneb » Sat Mar 17, 2018 10:45 am

I've heard that the MOSFETs on the RAMBo tend to fail "on", so it looks like you may need to send the board back to Ultimachine. (or take this as a sign the universe is telling you to upgrade to a DuetWifi and FSRs. :D )

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Re: Hot end won't turn off

Postby VAXHeadroom » Sat Mar 17, 2018 8:24 pm

I think what has happened is that the shell of the cylindrical heaters is connected to one of the leads of the resistor. This means that I've created a short-circuit between the two heaters. Additionally the new thermistor may have a lead touching the hot block and created a 'sneak path' for the control circuit. I haven't confirmed this yet - too many other project in front of the debugging task :)
I'll post what I find...

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Re: Hot end won't turn off

Postby VAXHeadroom » Sat Apr 07, 2018 4:27 pm

Sneak path confirmed. Once I electrically isolated the thermistor wires from the hot-end, the system works correctly.
Except that now I've damaged the thermistor (handling - my fault).
They apparently are no longer available?!?
Is there an upgrade path for a different thermistor?

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Re: Hot end won't turn off

Postby Xenocrates » Sat Apr 07, 2018 6:15 pm

Easiest upgrade is to an M3 threaded thermistor, such as this one. It's not exactly one I've personally used, but it is from the successor company to the folks who made the ones I've used. Alternatively, get an E3D hotend (or an SE300 or similar from Seeme), so that you can keep nozzles available and make use of heater cartridges instead of power resistors. I really, really like the E3D cartridge thermistors and PT100 sensors, as well as appreciating the ability to use silicone socks.

So, if you want a cheap fix, the M3 stud is easy, cheap, and robust. If you want to have long term support, pick a more modern hotend design. Or you can buy loose thermistors from folks like Filastruder still, if you don't want to upgrade.
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Re: Hot end won't turn off

Postby VAXHeadroom » Sun Apr 08, 2018 12:17 am

Thanks for the link, that one looks great. The B value is a bit different, so I think I'll have to update the firmware right?
Didn't really want to fully change out the hot end...

Xenocrates wrote:Easiest upgrade is to an M3 threaded thermistor, such as this one. It's not exactly one I've personally used, but it is from the successor company to the folks who made the ones I've used. Alternatively, get an E3D hotend (or an SE300 or similar from Seeme), so that you can keep nozzles available and make use of heater cartridges instead of power resistors. I really, really like the E3D cartridge thermistors and PT100 sensors, as well as appreciating the ability to use silicone socks.

So, if you want a cheap fix, the M3 stud is easy, cheap, and robust. If you want to have long term support, pick a more modern hotend design. Or you can buy loose thermistors from folks like Filastruder still, if you don't want to upgrade.

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geneb
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Re: Hot end won't turn off

Postby geneb » Sun Apr 08, 2018 10:33 am

The thermistor hasn't been discontinued, it's just sold out.

They should have stock on them shortly.

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Re: Hot end won't turn off

Postby VAXHeadroom » Sun Apr 08, 2018 1:24 pm

geneb wrote:The thermistor hasn't been discontinued, it's just sold out.

They should have stock on them shortly.

g.

OK Thanks. I looked around the internet and couldn't find them at either Mouser or Digikey. But those little tiny glass beads are not very robust system so the hard-mounted/threaded design has appeal for me :)

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Re: Hot end won't turn off

Postby geneb » Mon Apr 09, 2018 8:56 am

You could also buy the SE300 heater block. That takes the new cartridge thermistor and is a drop-in replacement for the older style HE280 heater block.

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Re: Hot end won't turn off

Postby Xenocrates » Mon Apr 09, 2018 11:44 am

Except I'm pretty sure he's got an old style Seeme hotend with the PEEK section, given he mentioned changing out power resistors for a ceramic heater.
Machines:
Rostock Max V2, 760W corsair modular PSU, PT100 enabled E3D V6 and volcano, self adjusting carriages, Raymond style enclosure
Automation Technology 60W laser cutter/engraver

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Re: Hot end won't turn off

Postby geneb » Tue Apr 10, 2018 8:26 am

D'oh. :D

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