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Solution for Blown Anet A8 Bed Mosfet on Main Board

anet a8 bed mosfetMy Anet A8 bed mosfet has blown up  – what now?

I have been asked about this question about the anet a8 bed mosfet a few times now.

So my advice was to add an external mosfet and use the output of the controller to switch it on and off.

Thanks to GearBest my order of spare main boards was delayed until a few days ago, and my printer is normally on the go – so I didn’t want to strip it down.

So the first thing I did was to run a new main board up with a power supply – to test it.

I was under the impression that you could run the whole board off the usb, same as the mega. But this is not the case you need power to the board from the 12v dc input.

Now getting the computer to recognise the board was easy – with the ch340 driver installed.

Connecting through the serial port at 115k baud the computer recognised the board in pronterface , but the ‘printer’ was not working – it had errors.

You need to connect the two thermisters, one for the bed and the other for the hotend before you can fool the board into thinking it is a working printer.

So with these now connected, I was able to switch on and off the bed with pronterface.

Switching it all off and now connecting the external mosfet as I had described in an earlier post.

Connect the control wires across r42, the gate resistor for Q1 the bed mosfet.

First thing I had to do was find r42, the second was to solder wires wires across r42either side of it.

Being an 0805 surface mount resistor you don’t have much space between the pads of the resistor, but it is possible to solder either side of it.

Note: an easier place to connect the wires is across the bed mosfet – the two legs are the same terminals as the resistor and wider easier method of wiringspaced.

Wiring in the supply to the mosfet board and putting a load on it of a car led indicator lamp – closest thing I had to hand which worked at 12v easily!, I switched it all back on.

Reconnecting the computer I switched the bed on and … nothing- no light – the onboard mosefet switched on but not the external one.

Ok so what is wrong.

Looking at the circuit, the control voltage goes through a full bridge – to make it polarity independent.

This will take 0.6v off either pin – so from the 5v controller output you need to subtract 1.2v – we are left with 3.6v.

This is fed through a 10k resistor (R5) to the opto device to pass current through a led – this in turn switches on the opto transistor, eventually switching on the output mosfet.

The point of this is, that with 12v on the control input there is enough current through the led to activate the device, but with 5v there isn’t.

Damn – what now!

Calculating the current through the 10k resistor with 12v ( (12-1.2- 1)/10k= 1mA) and with the 5v input ((5-1.2-1)/10k= 0.3mA) we can see why the opto switch is not working.

Note the extra 1v drop in the above equation is for the led internal to the opto device.

So working it the other way round – we need a minimum of 1mA to operate the opto device we can use the voltage to calculate the resistor value.

5-1.2-1 = 2.8v

To have 1mA flowing and calculate the resistor value we divide the voltage by the current.

2.8/0.001 = 2800 or 2k7

I am very lucky to have an 0805 resistor kit, so I looked through this and found the closest value was 2k7 (preferred value). Removing the fitted one and replacing it with the 2k7, reconnecting and switchingreplace 0805 resistor the bed on and off it worked.

So if your anet a8 main board has blown its bed mosfet you have three choices.

  1. buy a new main board – be it ramps and mega or(#amazon link) standard replacement.

  2. Replace the Bed mosfet(ebay link)– see below for directions on how to do this easily.

  3. Use the controller voltage but change the resistor value on the external mosfet board.(#amazon link) resistor kit

Replacing the onboard mosfet easily.

Note: remember these devices are static sensitive – pick up the device and then touch the board with a finger to get both the board and device to te same potential- reducing the chance of it blowing up!

I have just been reminded that you need to know the device number to replace it!
The device is an IRLR7843 mosfet.

Can be obtained  ebay sources in the UK or elsewhere dependant on time scales.

The onboard bed mosfet is located where the designator says Q1. It is under the silver heatsink.

This heatsink is held in place with thermal silicon adhesive.

To remove this heatsink, take a flat screwdriver and carefully lever the heatsink away from the device. This may pop off easily or be very difficult. If you use the board as a lever by the green connectors it is controllable – but be careful you don’t damage the board.

Once this is off you can see the device is held down to the board with two legs and the back pad.bed mosfet exposed

To remove this device easily – carefully cut the legs of the device close to the package.

Use a soldering iron to remove the cut legs- don’t damage the pads on the board.

To remove the main body, hold the tip of the soldering iron against the metal tab at the top of the device and feed a bit of solder onto the iron.

You will see the solder flow onto the tab of the device – when this happens it is ready to be removed.

Use a pair of tweezers to lift the device off the large rear pad and you have done it – congratulations.

All you have to do is to clean up the large pad – make the solder flat – and replace the device with a new one.

To remove the solder from the pad I use (#amazon link) solder wick.

To use this lay the solder wick over the solder you want to remove and press on top of this with the soldering iron, you will see the solder melt and flow into the solder wick.

Remove the solder wick from the area before the solder solidifies.

If the solder solidifies then remelt the solder with the soldering iron and remove it quicker.

Remember that this wick is copper and it will conduct heat – so keep your fingers a little away from where you are going to remove the solder. Or get asbestos fingers!

To replace the device

Melt a little solder onto the large pad. And I mean a little.

Place the device onto the pad and heat the tab.

Feed a little solder onto the iron while it is in contact with the tab and the large pad to assist reflow.

When the solder melts then position the device carefully with tweezers – making sure the two legs are on the correct pads, remove the iron.

Solder the two remaiming legs to their respective pads.

Now all you have to do is to glue the heatsink back on with this (#amazon link)thermal compound.

And you are done.

Now test the board – without loading it with the bed to start with.

So there you have it – how to replace your bed mosfet and how to wire in an external mosfet if your anet a8 bed mosfet blows!

It sounds complicated but really isn’t.

If you have a go at replacing your Anet A8 bed mosfet and have problems then why not comment in the box below and we can try to sort the problem out.

Thanks for reading


3d print journal : Polymer Igus bearings

Update to SB1 : replacing your bearings, Igus Bearings

A while ago I wrote a post about replacing your bearings. SB1Anet A8 upgrades : Anet A8 3d printer

In that post I had bought a set of bearings from China, they turned out to be very poor quality.

Even just running them up and down the rod I could feel that they would make the prints even worse than what was already on there. They were lumpy and grinding, I cleaned and oiled them to no avail.

So what to do. Continue reading 3d print journal : Polymer Igus bearings

3d print Journal 10-01-18 : Slicer Vase Mode

Happy new year to you all.Anet A8 upgrades : Anet A8 3d printer

Prior to the Christmas break I was printing with my Anet A8 3d printer.

I had the slicer vase mode set– if you haven’t tried it you must.

Vase mode produces, in some slicers, a continuous spiral – no steps in layers and only one shell thick no infill.

Great for vases!

But people have found that you can print other items, which follow the rules – continuous circuit on each level.

So a mathematical christmas tree and other objects have appeared.

The first slicer I tried with vase mode was KISSlicer.kisslicer logo

You have a lot more control over most things with this slicer and it can be very confusing to start with – it is really frustrating that most of these slicers call the same thing by a different name – just trying to be clever I think but to the end user it is very confusing.

Anyway, I had gone through a certain number of calibrations with KISSlicer and thought I was getting somewhere.

They have model which does not slow your printer down as a calibration piece. Download it here.kisslicer vase mode

So I was getting on with the vase mode ( found by sliding the infill slider to the right in the style tab) and not really being happy with the fact tat it would print like a normal print – with the z axis going up a full level each layer, but with no experience in vase mode how do you know different.

I started printing out the Christmas trees, and found a few problems -like minimum layer time – the printer would, at the top of the tree, raise the print head and wait then resume. The top would then not print properly.

Another reason to look at the sliced file before printing, so I did next time and thought I had cracked it – it was ok until about 1cm from the top where it did the same again, even with the min time per layer set to 0.

so enough of this I changed slicers, I went back to the one I think most people have used Cura.cura logo

Reading through some of the older posts on forums I came across the fact that in cura vase mode was called ‘spiralize the outer contour’ – vase mode is shorter and more descriptive!

Activate it by going into expert settings and click the selection.

old cura vase mode

So I tried a print in this and wow – I sat there for a fair few rotations of the christmas tree, watching the z axis continuously turning ever so slowly the print nozzle never stopping and the filament continuoulsy being fed.

What a joy!

The print – well there was no seam to start with, it was as people had described vase mode – a very thin single layer structure.

And it printed to the very tip with no problems!

I like the idea of KISSlicer and will go back to it in the future, but at the moment I am back with Cura, version 15.04.6 at least.

With the success of this I looked on thingiverse and downloaded a few more vase patterns – I can recommend the vases by  Ferjerez Mathematical creations which if you have scad you can play with.

Some of the vases and bowls absolutely stunning – thank you Ferjerez.

Printing some of the vases I noticed that in the overhangs there were gaps, looking for the answer online I read that this was due to poor machine setup, hmm what had I done wrong?

I had printed a few more things in ‘normal’ mode and came back to this.

Setting the slicer up and saving the gcode I printed another vase and waited.

This time the walls were thicker and it had all worked, even the overhangs had printed vase worked ok

Looking at the settings in Cura I had left the wall thickness at 0.8, printed with a 0.4mm nozzle. I didn’t think this was possible, but it did it, over extrusion maybe? But I don’t care it worked.

So I went ahead and printed a bowl from the same pack and again it came out with a thicker wall thickness sslicer vase mode green bowland was able to hold its shape well.

I downloaded the later version of Cura – 3.0.2 at that time and had sliced the same model, I need to sort out the start gcode so it acts the same as the old version and not drag the nozzle across the bed.find it here in later versions

I hadn’t really explored it with this program and updated to version 3.1.0, it loads so slooowly on my PC.

I downloaded another ‘ test your printer’ file by majda107 and h

ad sliced that in the latest Cura, saved it – had a quick look at the layers and copied it across to my sd card.

On printing it I thought something was wrong with my printer – the first layer would not stick and the further the machine got into the print the worse it was.

Using a screwdriver I was constantly adjusting the height of the bed – flashbacks of the old days when my Z axis endstop was loose – nope it still wouldn’t stick.

I happened to glance up at the display and saw the Z height at 0.8mm and thought – that’s strange it should be on the first layer, how come.

Then it dawned on me, my hand slid slowly around to the reset switch on the main board and pressed it.

The print head was slid across to the left and the mess on the bed was cleaned up.

Back to the PC to slice it again – this time untick the ‘spiralize the outer contour’ and slice it again.

Yes I did laugh and wonder at the software engineer who could have added something to the display to say that you are in a ‘special’ mode rather than standard mode. But no they leave you in the dark with most of this. And people wonder why 3d printing does not take off with the masses!!

yes I did check the layer mode more carefully this time and yes it did print more than just an outer shell. I do wonder what it really would have printed if I had left it and the layers had stuck together- would It be a ghost outline of the model which it was going to print?

So if you take nothing else from this – make sure you check that you are not going to print in vase mode when you expect something else!

And increase the wall thickness of vase mode to make your models a lot thicker and stronger.

I did notice when playing around with the later Cura 3.x.x you will need to exit the program and restart it to get the model to slice correctly.

Good luck with your printing. so go and have fun with your slicer vase mode.

Thanks for reading


Anet A8 bearing replacement- SB1

Service Bulletin 1 (SB1)Anet A8 upgrades : Anet A8 3d printer

This service bulletin details how to check and perform Anet A8 bearing replacement on the X and Y axis.

What are the symptoms which require Anet A8 bearing replacement

After you have bought your 3d printer and used it a fair bit you may notice a few strange noises.

Where the print head used to glide across the printer, you notice a knocking noise as it changes direction.

When the bed changes direction there is a visible jump.

Well the main cause for this could be wear on the linear bearings. Continue reading Anet A8 bearing replacement- SB1

Why you need a multimeter if you have a 3d printer!

What a digital multimeter can tell you.

You know that time when your printer went wrong and you sat there looking at it?

You were frustrated because you knew it was not mechanical, there was something wrong with the electrics or electronics.

Someone on a forum said – ‘ Have you checked the voltage at …’ and you thought huh?

Well that was the time when you could have done with a multimeter to measure the voltage.

The problem got solved eventually with a friend coming round with a meter and with a couple of checks he said ‘Yep I agree with them, it is the …’.

You just sat there and nodded.

So why not change that?

Anet A8 upgrades : Anet A8 3d printer
See what people think at Amazon – click the picture. (#amazon link)

You know how to put the printer together and operate it.

You have had a go at the cad thingy they are all talking about, and yes it’s ok – maybe with a bit more practise it will get easier.

But what if it goes wrong again?

What will you do then?

Well you could do worse than invest in a multimeter – or meter for short.

What does a multimeter do?

The most basic multimeter will measure voltage, current and resistance.

Any other ranges will be a bonus.

Meters now are capable of measuring capacitance, frequency, temperature and a lot more, all of this for really not a lot of money.

What would be the best multimeter for the 3d printer?

What would you like to measure?

The low voltages around the circuit.

The resistance of the bed and fuses.

The temperature of the hot end and bed.

Checking the cables of the motors and other items.

Checking whether the mosfets are working.

So you can see with a meter you can do an awful lot to fix and test your printer.

Which one is the best one – the one you use – if it is too complex you will look at it and put it to one side, never to pick it up again.

So go for one which will do the job, not the one that has x thousands of ranges to measure between here and the moon, you just need a meter which will measure what you want.

I would recommend something like this (#amazon link) Tacklife DM01M

With this one you even get a light to see what you are measuring.

With this meter you need to be aware of what you are about to measure – if you try to measure 12v on the 6v range it will just show overload, so you need an idea of what you are just about to do or measure.

But this is true when fault finding- if you don’t have any idea of what should be there, then anything you measure will be correct, as you don’t know it is wrong.

So on this meter for measuring the 12v power supply set the dial to 60v dc range.

Connect the black probe to the negative of the power supply ( black lead on the main board input) and the red probe to the positive of the power supply( red lead on the main board) and with the printer switched on the meter should read about 12v – there will be a little bit of fluctuation and you will probably be able to hear that fluctuation in the voltage on the fan on the extruder – this should be in the order of 0.1-0.5v.

Do use the meter when the printer is working so you have an idea of what voltages are expected where, so on the power input of the main board , when switched on, you will get 12v.

On the mosfet output to the bed you may not get 12v until it is on for a certain time period – the meter needs a certain time period to read the voltage. So it may try to fool you by showing 3 or 4V up to 12V and be varying. Watch the led on the bed and if you measure it after switching on the bed you should find it to be 12v, when the led is flashing on/off quickly the voltage will drop, maybe even down to 0v. This is quite normal, as I said the meter needs the voltage to be stable for a time period for it to measure the voltage correctly.

So have a poke around the circuit – do not short anything out ( connect two points together unintentionally) or you may let the magic smoke out -this would not be good, as you cannot catch all of it and put it back.

multimeter resistance measurement 1
Mine read about 130k

With your printer off you can measure the thermistors resistance, along with the bed resistance and the heater resistance.

All of these checks will allow you to determine whether the items are in good order.

The thermistor, when at room temperature will be about 100kr.

To measure this switch the meter to the 600k range, plug the leads into the com ( black) and the red into the one above that.

Unplug the thermistor from the main board and place a probe on each of the connections. As I said the meter should read about 100k.

Note; if the thermistor is hot the resistance comes down rapidly – this is how the controller is able to ‘see’ what the temperature is and switch off the heater.

You can measure the resistance of the print bed – again unplug the bed and measure between the two outer pins on the bed connector.

You should read about 1r, this may be more or less.

Or how about unscrewing the hotend heater and measuring the resistance of that.

heater multimeter measurement
my heater resistance was 3.3R

As it is a 40w heater run from 12v the resistance will be about 3.6r.

Get yourself a log book and start noting these measurements down for the time when your printer goes wrong.

You should also be noting down the filament type and what parameters you change in your slicer and printer to make it print properly, but that is another post!

If one of your motors stops working – you can measure the resistance of the windings and then check the continuity of the cable.

So you can see with a multimeter you can diagnose a lot of the faults, and I will try to list out some of them in another post and how to check for them. So why not sign up to be kept up todate with the posts in the box at the top right.

Why not hop over to Amazon and order one today.

If you do need help measuring anything with your multimeter then get in touch via Facebook, 3deeprinter, or add a comment below and I will be able to help you.

Thanks for reading


Anet A8 Mods – How to Make Your Own Heat Block Cover

How to make your own heat block cover

– don’t let the cooling fan spoil your prints

What Anet A8 mods have you done?

All FFF 3d printers use a similar technology, the heatblock.

anet a8 mods - covered nozzle
one of the most important parts – the nozzle

This is the way they get the filament from the standard 1.75mm or 3mm down to the 0.4mm to create your model.
The heat block is a lump of metal with a 12v ( normally – there are 24v ones) heater cartridge and a thermistor, to report the temperature.
These lumps of metal are hung below the printhead.
As the filament comes out of the nozzle and bonds with the layer below by melting into it. Continue reading Anet A8 Mods – How to Make Your Own Heat Block Cover

3d print journal 01-12-17 : bed screws binding

3d print journal 01-12-17 : bed screws binding

A tale of woe about the dilema to drill out the base bed screw threads or not, and what a lucky chap I am, how I overcame the problem and what you should do if you haven’t got to this stage yet.

And how I initially level my bed to prevent the nozzle crashing into the surface of the print bed.

Read on to find out what happened. Continue reading 3d print journal 01-12-17 : bed screws binding

3d print journal 28-11-17 : Anet A8 problems

More Anet A8 problems

Printing on the Anet A8 last night I heard a thump from upstairs, wingwhere the printer is located.

Going upstairs, I found a pen on the floor – obviously not liking the vibrations of the printer. Thinking that was it I went back to what I was doing.

Later I checked how the print was going, only to see that there was a shift in one or both of the axis, arghh! Continue reading 3d print journal 28-11-17 : Anet A8 problems

Anet a8 upgrades : Adding Led Light to See Your Prints

What Anet A8 upgrades have you done?

Buying a 3d printer is exciting.

Putting together an Anet A8 can be frustrating but rewarding.

what are we prinitng
what are we prinitng?

Printing with it is brilliant.

But one problem is that you cannot see what you are printing! Continue reading Anet a8 upgrades : Adding Led Light to See Your Prints

Anet A8 upgrades : External Mosfet for the Bed

Anet A8 upgrades : Anet A8 3d printerA lot of people are interested in the Anet A8 upgrades, especially the mosfet mod for the heated bed.

The reason for this is a lot of misinformation out on the web about the mosfet on the main board being too small and causing fires.

If you really want to carry out this mod then follow the directions in this post.

We will go through everything you need to do to carry this procedure out safely. Continue reading Anet A8 upgrades : External Mosfet for the Bed