Replicator 2 - No voltage on heater pins

[Matt LaRussa]

My heater cartridge shorted out when I replaced the thermal tape on it.  Instead of buying another, I retrofitted my E3D hotend to it.  I got the thermocouple working, but the new 24v heating element wouldn't warm up.  After significant investigation, I found that the heater pins on the mainboard are not putting out any voltage when I fire off a preheat.  I do not see any blown components on the board.  Voltage measured at the extruder fan was 21v.  New power supply or new mightyboard?   Mightyboard rev G running Sailfish 

[Jetguy]

You blew MOSFET on the board. Further, you failed measure correctly, you actually have 24V constantly to the heater, but unless the MOSFET on the return leg shorts that 24V return from the heater to ground, you have NO voltage ACROSS the heater.
Important concept to absolutely get before even trying to test any 3D printer board, ground is switched, not the + power side.
https://i.stack.imgur.com/BOQJt.png
YOU MUST place your meter lead negative on the power source negative to properly understand and diagnose the circuit.

Again, the heater ALWAYS has 24V live on it. ONLY when one side is then switched to the ground or negative plane of the circuit does electricity then flow through the heater.
If you take a meter and measure across the heater, only when in the on state AND the MOSFET is working, would there be a voltage read on the meter.
However, if you properly measure the circuit, you will then see that compared to the power supply negative, even when heater is NOT ON, both leads will then read 24v

Why is this so important? For both troubleshooting and understanding the circuit. Again, the problem is DANGER lurks from ignorance of the circuit. The heater is ALWAYS powered with 24V even in the off state. A short to either wire of the heater then shorts 24V to whatever touched. This is why thermocouples need insulated, but also why a short can result in the entire metal structure of the extruder becoming live with 24V and damaging anything else that touches it.

[Jetguy]

That mainboard is $500 to replace.
Highly suggest you either replace the MOSFET or get one of us to do it.

I will do it for free if you pay shipping of the mainboard back to you.
I have the required MOSFETs and know the board like the back of my hand.
This is the MOSFET https://www.nexperia.com/products/mosfets/n-channel-mosfets-25-v-30-v/PSMN7R0-30YLC.html
Here from Digikey https://www.digikey.com/product-detail/en/nexperia-usa-inc/PSMN7R0-30YL115/1727-4170-1-ND/1993023 , like I said, I have a few and at 76 cents, makes sense to buy a bunch rather than pay shipping for one or two. Hence, why I offered to do it for free, 76 cents- consider it a holiday freebe.

FYI, others have gone down this road https://groups.google.com/forum/#!topic/makerbot-users/OWfrwoBpzzU

Semi related, the FAN mosfets are ALSO easy to blow and don't even require a short to blow it https://groups.google.com/forum/#!topic/makerbot-users/_arqq2V-TQ4

The MOSFET failed is G8 or Q10 (wasn't clear which hotend on the 2X shorted or was non-op)

[Jetguy]

The other thing that could blow in a seriously bad event would be the inductors near the connector, but I would think they would show damage.
The MOSFET doesn't have to look blown to be blown.

[Jetguy]

Just as a follow on to this thread to give an answer, I was sent the board for testing and repair.
What was blown was the inductor on the extruder 1 heater voltage output. See for Rev G board, Makerbot was trying to pass FCC RFI/EMI compliance, and so on any wire leaving the mainboard they added tiny inductors in series with the outputs to block EMI/RFI. In the event of a short or overload, these inductors can blow open circuit like a fuse. This is why the heater was not getting the constant on 24V supply.

However, there was a secondary fault. The extruder fan that is temperature controlled (not the gcode print layer cooling blower style fan) MOSFET was also blown. As expected it was stuck on, but since it was blown it was not barely enough to spin a fan, just when open circuit with no fan attached the corresponding indicator LED was lit showing the on status- a classic telltale.

I cannot stress enough, these boards are expensive and they are "right sized" (to you and me, that's undersized) to the specs from the factory. There is NO room for error. If you fan needs oil, is stopped by dust, dirt or say filament or anything else, it can blow these tiny MOSFETS and then you have printing problems because you extruder overheats mid print.

[TobyCWood]

Wow...  GOOD advice.

Thanks!
I wonder if this would also mean that having the extruder fan vibrate because it's out of balance at startup is probably also not all that good too. As such I replaced ALL my extruder cooling fans with ball bearing fans.

[Will Stone]

Just wanted to thank jetguy for posting the follow-up and add a little info in case others are looking for similar troubleshooting. My rep2 threw the could not heat error and I measured 7V (while "heating up") across pins above carriage that are normally plugged in to heater.
I should probably mention that I live on a lifepo4 skoolie and have the rep2 wired directly to our ~26.6v-28v lithium battery bank (rep2 has been running great for years on this supply voltage).
Anyway, resistance was less than 30ohms I believe from pins that were plugged into mobo that go to heater (black and white). Ended up being just a blown inductor like you mention and based on the way you worded it I decided the machine would be fine without EMI shielding on that line so just cut off the blown up inductor and bypassed it with a little solder (see pics). Up and running again!

[Scott Lichtsinn]

That's why i always recommend in the case of a fan FET failure to just replace the fan that likely caused it, but i have also seen the fan wires break down in the umbilical from flexing and causing shorts and broken wires as well, so replacing the fan and checking the wiring to the fan is always a good idea.  I also replace those fan FET's with a higher current part.  I run fans on my printers that take more then the stock FET's would be able to handle, i think if i recall correctly without looking at the spec sheet they were rated for something like 125mA, the ones i replace with are rated for 3A continuous load and surges up to 6A, i have tested them on a test board to handle 3A no problem, but they do get plenty warm at that level.  But up to 1A they stay ambient temp no problem.

I replace a lot of fan FET's due to failing fans, if the fans are starting to rattle on spin up or growl as they start its classic signs of a fan with bad bearings, you an oil them but its a temporary fix at best, and 24v 40mm fans are cheap.  Just don't make the mistake of putting a 12v fan on, i've had a few boards that the owner put a 12v fan on instead, usually the fan runs a little while then dramatically blows up and shorts and takes the FET and inductor with it.

[Scott Lichtsinn]

A solder blob works just as well as the dang inductors.  Just another pain they changed on these boards for EMI/RFI acceptance.

On a few of my printers i replaced those inductors with 2A fuses, just as an experiment, i haven't blown one yet, but my thought process is if and when a heater fails or if it gets shorted out it should just pop the fuse and leave everything untouched.  I would think it would be quick enough to save the FET, time will tell.

[Scott Lichtsinn]

Ball bearing fans are a good choice, but still keep an eye on them!  I have been running ball bearing fans on mine for a couple years now, problem is as they age due to being in a heated environment, especially on a fully enclosed printer, they start to wear just as much over time and can take a little more current on spin up as well.  I have measured some of the fans i have, all respectable brand name fans from a US supplier, they start out around 70-80mA, but as they age they start taking 120-150mA, i suspect as the lubrication in the ball bearings break down with age and heat but i can't say for sure that's it.  They do last longer then sleeve bearing fans, but they don't last forever.

[TobyCWood]

I would add... when replacing a fan pay VERY strict attention to the polarity of the original and do NOT just plug a connector in without inspecting. I have found multiple times where fans have the polarity reversed on the connectors, Reversed polarity can easily damage the board.

BTW... these days its way less expensive to simply replace a problem Mightyboard with a brand new, fully featured, 32 bit Duet wifi.

[Will Stone]

good to know - do you have a recommended upgrade/conversion guide for the duet2? Worth the time/money to replace a working mightyboard? I assume you're talking about this (official site here)

On the topic of mods/upgrades (e.g. putting fuses where inductors were), anyone here opinions for must-do mods?

I perused the non-printed upgrades thread, but some of it seems outdated and/or unnecessary - if you were setting up a new rep2 are there any upgrades you'd personally be sure to do other than 

1. latest sailfish 

2. upgraded build plate (i use glass attached with dual lock 3m) and maybe 

3. cnc lever/plate ?

After 2,600 hours of printing, my biggest (and recurring) issues generally relate to the hot-end and thermistor... (and it would be nice to have cloud/local network print controls). Does anyone have experience with an upgraded hot-end, like this one I have sitting in a to-do bin? Worth swapping?

Would post a new thread but don't know if the traffic to the group makes it worthwhile... Also not 100% sure this topic doesn't already exist and I just missed it when looking.... thanks for any input here!

[Scott Lichtsinn]

Just my opinion, the Duet boards are ok, but for about $150 USD i can repair a Mightyboard a lot cheaper.  Most of the boards that cross my bench are under $100 worth of repairs, some of them are around $50-60 and they are back in the mail to the owner.

On the Rep 2/2X series boards about the only mods i generally perform and recommend is replacing the Fan FET's with the higher current part, and if your worried about blown inductors you can swap in fuses, but the fuses are soldered on as well, so either way your going to blow a fuse or an inductor, but from my experience the fuse generally blows more gracefully, whereas the inductor usually blows and does some burn damage around it.  However, i have to source some more fuses, the last batch i had i run out of fuses and the fuses i was using went out of stock, so i started putting zero ohm resistors on, acting as a jumper that will still blow up pretty fast in an accidental short.

That extruder you linked to is a Bowden setup... All i can say is yuck.... I despise Bowden extruders, to the point that i have replaced Bowden setups with direct drive extruders.  I had way to many print failures and problems with the Bowden extruder that was on a printer at one time that i swore them all off.  Converted that printer to a direct drive and no more issues.  However if you have the stock Makerbot extruder drive then i can definitely see you getting frustrated with it.  Pitch the Makerbot extruder drive and replace it with an all aluminum spring loaded drive assembly and you will print without much trouble.  I have five Makerbot printers running daily here on my print farm, they all have upgraded aluminum drive assemblies on them, they aren't hard to find and they are cheap if you get the ones made in China off Aliexpress or eBay, some under $20, it makes all the difference.  Most sellers call them the MK10, for Mark 10 extruder.  Just be careful if you get one not to confuse the Rep 2 with the Rep 2X, they are different thicknesses to match the width of the mounting bar for the extruders.

If you really want the printer to be on WiFi there is other options, i have a unit that i am testing that allows communication with the printer over WiFi, it just plugs into the printers USB port.  After i have tested it more i can give you the details on that.  So far i have been able to get the printer connected to WiFi and then from Simplify3D i can send a file to the SD card and start a print, so it basically uploads the file to the printer and then i can tell it to print from that file.  Its still in its Beta stage, the guy that designed it gave me one to test, hopefully it will come to market in the near future as i see it being quite useful since i have my printers in a separate room, i could send print jobs remotely from my computer as needed!

The Rep 2 has a really good extruder setup other then the original Makerbot tension drive they put on it, but the rest of it is a really solid performer.  I find it hard to believe going to a Bowden would improve it at all, in my opinion its a downgrade.  But i like to print things like TPU, and i have never got that to perform perfectly with a Bowden setup.

[Will Stone]

We travel full-time so generally don't have a shipping address for more than a couple days - so I typically order from amazon but can't find a suitable aluminum spring loaded drive assembly on there - any suggestions for URL / source? The ones I found would require 3d printing a carriage rack to fit the rep2...

Got the toshiba flash air card up and running now that I finally put sailfish on the machine - and that solves my wifi needs :)

The lure to me of the bowden tube is it enables me to leave my work-desk platform setup on top of the 3d printer - leaving only about 2-3" of space for filament to slip underneath - which is much better suited to a tube than my old just-let-the-filament-rub-against-the-ikea-laminate-edges method with the direct drive.
So far my experience with the e3d hot-end (i installed it while waiting for parts to fix my original hot-end) is not stellar - but that's probably due to the makeshift thermocouple I hacked together and stuffed inside a molex-pin (and crimped it a bit) before tightening the set-screw...