Pro2 hot end won't cool down (board issue)

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RonniCox1
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Pro2 hot end won't cool down (board issue)

Postby RonniCox1 » Wed Jun 19, 2019 8:52 pm

Another problem with one of the printers at our Makerspace. We've sent in a ticket to support, and have been going back and forth for a while now, so I figured I'd come and ask if anyone here has any advice.

Essentially, the moment we turn on this machine it starts heating up the left hot end, and nothing we can do short of turning the machine off will cool it down. It's unusable, especially since the dual extruder won't simply let me use the right nozzle if the left is unplugged.

Just before this, one of our technicians accidentally sparked something that blew a fuse while doing repairs. The fuse was replaced no problem, and the motherboard looks fine otherwise (no visual damage), but I assume something has been damaged causing this issue. Does anyone have any idea what it might be?

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Noren
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Re: Pro2 hot end won't cool down (board issue)

Postby Noren » Wed Jun 19, 2019 9:04 pm

I can’t say for sure. But random errors are often caused by a broken flat ribbon cable. The flat one from the extrude board. I have replaced mine twice. There is usually extra cable tucked up inside the machine. Drag out a new part. Crimp a new contact and reattached.

Jetguy
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Re: Pro2 hot end won't cool down (board issue)

Postby Jetguy » Thu Jun 20, 2019 1:01 am

RonniCox1 wrote:Just before this, one of our technicians accidentally sparked something that blew a fuse while doing repairs. The fuse was replaced no problem, and the motherboard looks fine otherwise (no visual damage), but I assume something has been damaged causing this issue. Does anyone have any idea what it might be?


Yes, the answer is simple, #1 know that FET transistors tend to fail in the ON state (hence runaway heaters) and #2 Know that those FETs are located on the mainboard in the base, NOT on the extruder breakout and #3 There is a separate 3 Wire cabled carrying the 24V positive and 2 ground returns for the heaters from the extruder breakout.

Again, without a shadow of doubt, you've blown the hotend FET at the mainboard, it failed in the on state. There may or may no be visible damage to the FET, but between the failure symptoms and the known tendency to fail on, this is a sure bet.
If you want to validate this fact, it's extremely simple- unplug the 3 pin cable at either the mainboard or the extruder breakout. That disconnects the heaters electrically but leaves ALL other parts connected (temp sensors and fans via the separate cable). The mainboard has LEDs near the outputs showing when they are on- so if they are on the instant the board is on- there is your answer.
The PRO2 followed this same convention as the N series before it to be partially backwards compatible.
Last edited by Jetguy on Thu Jun 20, 2019 2:33 pm, edited 1 time in total.

Jetguy
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Re: Pro2 hot end won't cool down (board issue)

Postby Jetguy » Thu Jun 20, 2019 1:08 am

Also case in point when troubleshooting, these and 99.9999% of every printer on the market uses ground switching, not positive due to the ease and efficiency of using N channel MOSFETS. This means that when working on this printer, the heaters are constantly supplied 24V anytime the power supply is on. Only when the corresponding ground wire return to the mainboard in the 3 wire connector is shorted to ground by the transistor, then the heater is on because there is a voltage across it. This means from a troubleshooting and repair perspective be EXTRA careful and never work on this printer powered. Again, even if the heater is not on, when the power is on, there is a constant 24V present. That's likely what contributed to the spark and failure.

Jetguy
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Re: Pro2 hot end won't cool down (board issue)

Postby Jetguy » Thu Jun 20, 2019 2:37 pm

Further, if you want to print with this failed mainboard (not recommended, but in theory possible- well not really but.....), you must disconnect the heater cartridge at the breakout board at the extruder for the failed side, but do not disconnect the thermocouple. That said, I thought switching extruders requires both to heat for the mechanical movement system of the nozzles, and if it cannot heat, I would think that step to change to the active nozzle cannot be changed to because the script function that heats the nozzles would just hang until firmware timeout- maybe even invoke after time and safety limits.

I would definitely contact support on this one, and again, from where I'm sitting, there is zero doubt the mainboard has a failed FET and thus would need to be replaced.
Last edited by Jetguy on Thu Jun 20, 2019 2:44 pm, edited 1 time in total.

Jetguy
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Re: Pro2 hot end won't cool down (board issue)

Postby Jetguy » Thu Jun 20, 2019 2:43 pm

https://help.raise3d.com/support/tickets/new

Replacing the mainboard after you get one.
https://support.raise3d.com/Pro2-Series ... 4-108.html

Again, one of the 3 FET transistors that are in a line between the 2 fuses is blown and internally shorted constant on.
The LRU (Lowest Replaceable Unit) is the entire board.

RonniCox1
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Re: Pro2 hot end won't cool down (board issue)

Postby RonniCox1 » Sat Jun 22, 2019 7:45 pm

Jetguy wrote:Again, one of the 3 FET transistors that are in a line between the 2 fuses is blown and internally shorted constant on.
The LRU (Lowest Replaceable Unit) is the entire board.


Thank you so much for your detailed reply! My manager was hoping we could get around replacing the entire board, but since that's looking impossible at least we know exactly what the issue is, and how to avoid it in the future! We talked with support already and they said they'd never seen this issue on the Pro2s before, so all they could suggest was buying a new mainboard. We're doing that soon, hopefully.


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