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Heaters disabled - power panic sense fault?  

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nicholas.g9
(@nicholas-g9)
New Member
Heaters disabled - power panic sense fault?

TLDR: Bad nAC_FAULT line on my Einsy RAMBO stops the printer working, can I have it replaced?

I built mu PRUSA I3 MK3 from Kit form last week and it worked well for about 1 day then started having a problem when it stopped in the middle of a print. The original symptom was a "Thermal Runaway" message. Having checked the thermistors all worked and were reporting correct temperatures I retried and got the same problem. This time a bit sooner into the print and as I was watching I noticed that the heaters (bed and nozzle) stopped heating long before a message appeared. I tried a different print and it stopped even sooner. Then it would not even preheat.

I checked PSU voltages, thermistor operation vs a thermometer and upgraded to the new 3.2.0 firmware. Finally looking through the Einsy RAMBO schematics I noted that one thing that can kill the Bed and Nozzle heat is the nAC_FAULT line. I looked at that (from J19 pin 3) and saw that although it starts at about 2.7V when turned on from cold it drops over time and at around 2.35V the heaters are disabled. This is repeatable, and the longer I leave it turned off the longer it takes to drop to 2.35V.

I disconnected the power panic line from the psu to the rambo and saw exactly the same behaviour - not the power monitor board then. I suspect the 2.7V zener which clamps the nAC_FAULT line voltage on the Rambo is the culprit but as it's a tiny surface mount component there's not much I can do about that.

Is it time to return the Einsy RAMBO as defective or am I missing something?

Posted : 17/05/2018 12:47 pm
PJR
 PJR
(@pjr)
Moderator
Re: Heaters disabled - power panic sense fault?

Contact Prusa support via chat on the shop pages and give them a link to this thread.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 17/05/2018 1:32 pm
TJH
 TJH
(@tjh)
Eminent Member
Re: Heaters disabled - power panic sense fault?

Please let us know what you find. I've been looking into this as well.

I don't know that I'd say that disconnecting the power panic connector from the board and seeing the same behavior proves that it's the einsy and not the power panic.
Looking at the schematics for both of the boards, I think that the power panic board pulls the output down when AC power is OK.
On the einsy, there's a 10k pullup resistor from the power panic input (J16-2) to VCC (5V)

By my read, when AC power is OK, the FET on the power panic board is on, and the input to the ATMEGA is low.
When the AC power is off (or the connector is disconnected), the nAC_FAULT signal is high.

Edit--I retested my printer and it works fine with the power panic disconnected. Easier for me, but not as fail-safe.
There should be no need to feed voltage into the board.
I did look up the zener value--it's a 5.5V zener intended as transient protection.

Posted : 17/05/2018 3:25 pm
nicholas.g9
(@nicholas-g9)
New Member
Topic starter answered:
Re: Heaters disabled - power panic sense fault?

I have disconnected the power panic feed from the PSU and I'm feeding 3.0V into the power panic connector. The printer is now working fine and has just completed a 2h 26m test print.

The MK3_Power_Panic design on github ( https://github.com/prusa3d/MK3_Power_Panic/blob/master/rev.04/power-panic.pdf ) shows a design which pulls the power panic LOW (0V) when mains power is NOT present if I read it correctly.

Posted : 17/05/2018 4:54 pm
Tiago
(@tiago-2)
Reputable Member
Re: Heaters disabled - power panic sense fault?

This happen to me when i got a power outage, i use a APC Back-UPS 1400VA 230V, heaters go down but printer continue to print and do the moves util thermal runaway error come. When power resume heaters come back. Can this be the cause even with a UPS?

Posted : 18/05/2018 12:20 am
PJR
 PJR
(@pjr)
Moderator
Re: Heaters disabled - power panic sense fault?


This happen to me when i got a power outage, i use a APC Back-UPS 1400VA 230V, heaters go down but printer continue to print and do the moves util thermal runaway error come. When power resume heaters come back. Can this be the cause even with a UPS?

No all UPS are equal. It is possible that there is a short outage being passed to the printer, but that does not explain why the heaters son't turn on almost immediately. This would tend to indicate there is a problem in the PSU sensing circuitry.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 18/05/2018 9:57 am
Tiago
(@tiago-2)
Reputable Member
Re: Heaters disabled - power panic sense fault?



This happen to me when i got a power outage, i use a APC Back-UPS 1400VA 230V, heaters go down but printer continue to print and do the moves util thermal runaway error come. When power resume heaters come back. Can this be the cause even with a UPS?

No all UPS are equal. It is possible that there is a short outage being passed to the printer, but that does not explain why the heaters son't turn on almost immediately. This would tend to indicate there is a problem in the PSU sensing circuitry.

Peter

Well i can't test with other UPS buy my history is:

MK2s + APC Back-UPS 1400VA 230V + Power Outage = All Works
Then i sold mk2s, and the UPS
I buy a new mk3 and new same model UPS.
Now mk3 + APC Back-UPS 1400VA 230V + Power Outage = Heaters go down.

Tried manual switch of, bed at 60ºc and same behaviour happens.
I have all "smart" feature off.

Soon i will move to a enclosure with a proper 24V 20A PSU, i hope the new PSU able to fix this problem... If the power outage is short, like few seconds no problem at prints, but if minutes of outage it will ruin the print.

Posted : 18/05/2018 3:02 pm
rahul.j
(@rahul-j)
New Member
Re: Heaters disabled - power panic sense fault?

Hi I am facing the same problem. I'm using an Apc 1000va 230v ups. When there is a power outage heating stops the printer continues to work. Has anyone found a solution for this. Thank you

...
Posted : 14/08/2018 9:42 am
Tiago
(@tiago-2)
Reputable Member
Re: Heaters disabled - power panic sense fault?

well not me, even with a new power supply more capable with some offline cap power same thing happens to me...

Posted : 14/08/2018 4:05 pm
The Vede
(@thevede)
New Member
RE: Heaters disabled - power panic sense fault?

@nicholas-g9

Hi, reviving this old thread as I have been having the same problem that you described and would like to try applying 3.0 V to the power panic connector as you described.  Just want to check first - did you apply the voltage to the black and white cable leading to the power supply?  Or to the corresponding pins on the Einsy Rambo?  

Thanks

Posted : 07/12/2019 11:25 pm
Alex
 Alex
(@alex-3)
Active Member
RE: Heaters disabled - power panic sense fault?

I have discovered that you can unplug power panic sensor cable (black/white from PSU) to get Prusa work from UPS. Surely, you lose power panic feature, but it should be partially restored by your UPS.

Posted : 29/04/2020 4:56 pm
Alex
 Alex
(@alex-3)
Active Member
RE: Heaters disabled - power panic sense fault?

https://github.com/prusa3d/Prusa-Firmware/issues/2650

Posted : 02/05/2020 9:43 am
e.g. John Doe
(@e-g-john-doe-2)
New Member
RE: Heaters disabled - power panic sense fault?

I've been chasing my "Thermal Runaway" message problem with the hotend for a couple of months. The symptoms changed over the course of trouble shooting. The initial Thermal runaway problem happened overnight during a long print.

1. I had some initial success by adding a hotend silicone boot and performing the nozzle temp calibration M303 sequence. However, the problem would reoccur at times.

2. Finally, I had a complete failure to heat the hotend. The thermistor tested good and the heater cartridge resistance was ok at about 15 ohms. The 24V power supply was putting out 24 volts. The heat bed would heat to temperature just fine, with minimal droop on the 24V PS. When the nozzle heater was turned on, I would only see 0.8V across the heater cartridge. Aha - the Einsy board had a bad FET.

To test that theory, I manually connected the heater cartridge direct to the 24V PS via a momentary switch. Viewing the temp on the info page, the temps quickly went to the setpoint and I was able to manually keep the hotend at the the setpoint by toggling the pushbutton switch for a second or so to maintain temp.

My guess is that the driver Q1 driver FET has been going bad for a while and finally totally failed - allowing me to identify the problem.

My next step is to attempt a board repair by replacing the PSMN1R8-40YLC,115 Q1 FET. Those are $1.35 at Mouser. A new Eisny board is $170, so it's worth the trouble.

Posted : 23/09/2020 8:38 pm
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