P802M Prusa i3 Unofficial Support Thread

Issue: Having problems with my LJ18A3-8-Z/BX sensor so z-probing doesn't work.
Problem: LJ18A3-8-Z/BX wired up to a voltage divider and the readings are as follows.
12 V from printer PSU.
Reading before voltage divider is 10v when light is off and 0V when light is on

Readings after voltage divider.
Plugged into printer light off 4.5V
Plugged into printer light on 2.8V

Unplugged from printer light off 4V
Unplugged from printer light on 0V

Printer z endstop voltages are (S) 5V ( -) 0 V
Just made a discovery and measured the (+) pin on the z end stop and it's actually 12V

Changed, modified and uploaded so many tweaked versions of Repetier firmware 92.9 that I can do it blindfolded now.....
The G31 signal of probe sensor always stays in one state, either H or L, and only changes when modify I #define Z_PROBE_ON_HIGH 0 or #define Z_PROBE_PULLUP 1( I can't remember) but still wont change when the light goes on or off on the sensor.

IT'S DRIVING ME CRAZYYYYYYY @_@

The printer is here with me at work and I need to get it up and running before the students turn up for the new term as I won't have time to tinker for the next few months over weekdays :-(

And thanks for posting your info robmilr. It looks similar time mine but in your case your probe works.
Oh and I'm sure there used to be a red LED on the Melzi board but after updating the firmware it doesn't light up any more...
I've gone back to the beginning of the thread and I can't see anyone with the same issue.

:'(
Possible fix / solution: Read the following post by Robmilr !

Edited 7 time(s). Last edit at 09/15/2016 06:35AM by Gatchaman.

Not quite sure but sounds like one of the problems I had at first - I used 18K and 33K resistors for the voltage divider, and that resistance is too high for the small amount of current going through, so the firmware always reads it (even 2.8V) as logic '1'. Try smaller resistors -- you can work out current with V=IR since you know V and R, then using the value for I work out what value for R you need to get the lower voltage. If you have a hard time sourcing resistors (like me) Google 'resistors in parallel' and you will find that you can halve the resistance by using 2 resistors (same values) on each side of your voltage divider.
good luck,
rob.

Possible fix / solution: For problems with my LJ18A3-8-Z/BX sensor so z-probing doesn't work.
Will look into asap.

I built my divider out of 2x 18K and a 8.2K.

Will drop the 8.2K for a lower value.

On second thoughts will start a new divider from scratch and will utilize the 12V direct from the Melzi board and plug the old end stop back in as a fail-safe switch.

So near and yet so far :-)

I've got 4.7K, 5.6K,8.2K,10K,18K and 47K on hand.

Update: Used 10K and 5.6K resistors to make the voltage divider and G31 shows a change in probe state!!!!!

THANK YOU ROB!!!!!!!!!!

A quick G32 after a homing the extruder and the probe now works!!!

Rob, you're the best. Can't thank you enough dude.

Edited 9 time(s). Last edit at 09/15/2016 06:46AM by Gatchaman.

Quote
robmilr
I think this effect has been the result of filling in air gaps between the bed heater and the build plate, rather than something special about the coefficient of heat transfer between iron and aluminum. If this is the case, you may be able to speed up your bed heating time with a few layers of aluminum foil (I would place shiny side up towards build plate) between the bed heater and the build plate.

I've done some more experimentation today, sadly it seems to me that it really is the steel heating up so well -- stuffing the gaps with aluminum foil doesn't seem to help any. OTOH the piece of scrap metal gets screamingly hot compared to the rest of the bed, so (a) maybe I'm just heating up the thermistor better and (b) bodes well for the stainless steel build plate I have on order.

To cut a long story short I've been using the wrong configuration.h file to tweak the firmware but that's sorted now. Correction. Uploading the P802M config.h to Repetier configurator would return some certain options back to default nullifying the original file, and if you haven't a clue as to what is what and uploading the firmware to the Melzi then a lot of things wont work in Repetier.

The final piece of this 3d puzzle is the hot stuff.

Can P802M Melzi board users please post their hotend and heatbed settings from their configuration.h file or simply point me in the right direction.

In the mean time I'll scan the [github.com] and compare it to my conf.h for clues on how to set it up.

Got it sorted in the end but came up with another issue when matching configuration.h settings.

When I enable INTERPOLATE_ACCELERATION_WITH_Z 1 and try to upload I get "Sketch uses 130,084 bytes (100%) of program storage space. Maximum is 130,048 bytes." Basically the sketch is to big. But when I disable INTERPOLATE_ACCELERATION_WITH_Z 0 then I can verify and upload to the melzi board.

Has anyone else had this issue and how did you solve it? Can I enable it some other way?

Solved the issue by cutting down start up scripts with only 2 bytes to spare.

Edited 4 time(s). Last edit at 09/19/2016 05:03AM by Gatchaman.

Quote
Gatchaman
"Sketch uses 130,084 bytes (100%) of program storage space. Maximum is 130,048 bytes."

yup, Melzi just ain't big enough. Sorry, can't remember what I turned off, but went ahead and ordered one of the 12864 display + RAMPS + Mega kits off Amazon when I ran into that. Just received it this evening, next to figure out how to mount the display -- but at least it is standard, so I can switch to Marlin easily too now.

Bought one of those kits from the bay about a year ago. It's been under my desk for the same amount of time.
Looking to build a Ultimaker clone of which all the parts are here. Just need to transport the gear home and start fiddling.....

Back to the P802M. I think my steppers are running too hot in my cardboard box enclosure. Getting very stringy supports and sometimes Repetier will have a print waiting go but the P802M wont budge. I have since found out it's a safety feature built into the steppers or Repetier. Apart from getting a multimeter out and tweaking the voltages anyone got any M or G codes I can use to send to the melzi board to lower the current. Either that or I'm going to have to bug everyone in my office when I print stuff with the enclosure off.

The heatsink on the extruder never fitted in the first place. I think the bolts holding the stepper motor onto the extruder carriage were a couple of ml too long so there is a relatively large gap between the heatsink and the extruder. Great :-(.

Yep. Open air printing seems to have sorted the issue....

Edited 4 time(s). Last edit at 09/20/2016 03:34PM by Gatchaman.

On and off been having issues with the temp sensor in the extruder for this little unit.

Pretty sure now it's the thermistor that has either died or developed a break.

I'm pretty sure it's a 100K thermistor, but which one?

which makes me wonder - is there a parts list for these units? or something resembling a parts list? got to know where to start searching for replacement bits...

Or just a pointer on where to look for an appropriately sized replacement bit (presuming it's not just a matter of me dusting off my soldering skills...

Upload the configuration.h file from the P802M github to the Repetier firmware configurator and click on feature tab then heatbed and or extruder and look down the options and you should get to a point where, after a click or two, it lists the thermistors that are known to work with our printers..... I think. Come to think of it you don't have to upload anything, just click on the features tab

If you check back through the thread you'll find the info. I'm sure I've seen the type of thermistors mentioned somewhere here.

Quote
davidmilunic
Awesome job on the RC5!

I was a bit frustrated with the original firmware supplied by Zonestar.
The autolevel never seemed to be right, particularly the very last corner that it would probe.
It always reported it as 2mm higher than all the other spots (which couldn't be possible).

!

You would probably need to change your probing grid to be away from that corner where you have a metal screw....
It is possible that the probe is getting to sense that.

Lovely to see so many people in here...
after having near getting fire on my printer, I had to re-build my bed support.

I upgraded my bed heating system via SSR Fortek DD25A
I believe I might wired it wrongly and the SSR got shorted and was allowing the bed to be infinitely heating up....
Plus, I put a foam under the heated bed to get faster and higher temp.

well, it melt the foam and the acrylic bed support was all deformed.

now I build a wooden base support and I am back on line..

this time installed an SSR of DD40A sit on a heat sink with a temp probe with a 12V fan.





Got tired of the inductive probe that has only 4mm sensing distance (I know there are the 8mm's), plus the aluminum is not that inductive, the sensing distance gets close to 1.2mm....

Now I have upgraded to a SUNX reflective sensor; an adjustable range sensor (recycled from scrapped automation unit from the work)
it is much easier to adjust the distance and using the Z offset to fine tune it....

As you can see, I am testing a pad on top of the heated bed.
it ai a cutting board from dollarama for $2

it is a little bit challenging, but I am getting there.

Will let you guys now.....

I don not like masking tapes.... nor glass.

will keep you guys posted about my testing on that pad.

cheers!!

Edited 1 time(s). Last edit at 09/22/2016 01:20AM by Bobyni.

Quote
glimpse79
In these days i had big trouble with my zonestar prusa, prints suddenly hangs after a variable number of hours (1 to 4), the problem happens either using serial and SD card.

I thought it was caused by too much ambient heat but it happens even at night; any ideas?

Thanks in advance

I hope you have resolved your issue.

if not, try adding a dedicated 12V fan and blow directly onto the stepper driver chips (X, Y)
I believe you should see immediate result.

cheers

Finally sorted out z-probing with a LJ18A3-8-Z/BX ...
After running G32 S2 and disabling the heaters, and running a print, the nozzle ALWAYS dug into the blue tape no matter the settings for the z-probing until I thought that 3D goes in + and -.

I took a chance and changed one thing in the configuration.h, an upload to the melzi, and boom!!! The nozzle floats just above the heatbed instead of digging into the blue tape.

That took me fraking agessssssssss to figure out.......

Edited 2 time(s). Last edit at 09/22/2016 07:09AM by Gatchaman.

Do you have any Arduino programming knowledge? I'm thinking of stripping out the language code in the sketch. If the code for choosing a different language is stripped out I've got a feeling a bit more can be done with the melzi. When I first got a warning of the sketch being to big I had a go at cutting the sketch up but gave up after a while.

Will have to do a crash course in programming the Arduino!!! I'll ask at the Repetier forum at some point if it's possible.

Good luck with the RAMPS kit!

SOLVED:

so, I took the offending extruder heater blocks apart just to see what is what...

first thermistor almost fell apart in my hands - corroded. Now I know what the problem is.... very thin wire, hard to tin, stiff.

resoldered both as robustly as I could, suddenly started working flawlessly...

but there is clearly a design improvement possible here....

TIP: Not sure if this has been posted before but If you cut the filament holder base you can do this.

Was going to print a filament holder to stick on the top of the printer but I looked at the original holder, and thought....just cut the thing.

So cut it with a dremel. Put it on the printer, and it works!

If you do this then you do it at your own risk!

Edited 2 time(s). Last edit at 09/27/2016 11:18AM by Gatchaman.

Looks like a good idea Gatchaman.

Can anyone help me with the extruder heat sink .

When the heat sink is placed in position it isn't flush with extruder. The two bolts that hold the extruder stepper in place stick out by ~1mm so the heat sink doesn't actually touch anything. So I'm left with a ~1mm gap between the metal block and the heat sink.

I'm trying to dremel a space for the bolt heads to fit into so the heat sink is flush but I'm just asking if anyone has experienced this issue before.

Kind of fixed the issue with a lot of dremelling and a bit of foil.

Edited 1 time(s). Last edit at 09/28/2016 11:01AM by Gatchaman.

Quote
Gatchaman
Can anyone help me with the extruder heat sink .

When the heat sink is placed in position it isn't flush with extruder. The two bolts that hold the extruder stepper in place stick out by ~1mm so the heat sink doesn't actually touch anything. So I'm left with a ~1mm gap between the metal block and the heat sink.

I'm trying to dremel a space for the bolt heads to fit into so the heat sink is flush but I'm just asking if anyone has experienced this issue before.

Kind of fixed the issue with a lot of dremelling and a bit of foil.

I have reread your post several times and cannot visualize the problem you are describing. Can you attach a picture? I have 4 of these printers and have not experienced the problem.

I have just built a 3dcstar p802-MSH from gearbest. I have assembled the printer and all axis are working and the printer homes but when I start to run the pla heating file on the software the printer refuses to heat up and the two thermisters read DEF. What is going on with my printer?

Will see what I can do but for now my fix seems to be doing the job.

I'll post a picture soon to show you what I mean. To the left of the blower fan you have the heat sink and fan. It's bolted to the extruder. Underneath that heat sink you have two bolts that hold the extruder stepper motor in place. It's those two bolts that stick out too far causing the heatsink not to be flush. I think that heatsink is there to make sure the filament doesn't get too hot before the right time.

Oh! And I just had the fun of one of the power cables for the heatbed falling off. Took me hours to fix as I'd, cough, glued down the nuts holding the heatbed together.......

Home time!

Managed to print 2 x anti-z wobble things and it looks like the issue has been resolved....

The maker of the anti z-wobble thing neglected to mention that you have to remove the extruder heatsink and fan as the anti z-wob blocks the extruder from x homing!!!!!!!! .
This might help though "Hesine Prusa i3 M-505 X-End shifter"

Edited 4 time(s). Last edit at 09/30/2016 01:36PM by Gatchaman.

boba1000 : start a new topic instead of replying to someone else's with your problem if you want some answers.

---

Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

I'm pretty sure you've heard this before. I just finished assembling a Prusa i3 M-505 and I have NO IDEA what to do now. My specific question at this point is how do I limit the movement of the extruder? When I try to anything it moves outside the bed parameters and below or actually hits, the bed. I can't get help from the sellers. They got their money and simply don't care.

Any help would be greatly appreciated. Tony

Quote
MiniMfg
I'm pretty sure you've heard this before. I just finished assembling a Prusa i3 M-505 and I have NO IDEA what to do now. My specific question at this point is how do I limit the movement of the extruder? When I try to anything it moves outside the bed parameters and below or actually hits, the bed. I can't get help from the sellers. They got their money and simply don't care.

Any help would be greatly appreciated. Tony

I am not familiar with the M-505. Is it auto levelling? Did you follow the setup instructions on the sd card?

Gerry

Yes. At this point: When I hit Start print, the extruder moves all the way to the stop on the left and stays there. Then the temp starts to rise. Every time it hits 240 degrees which I think is too high I hit the emergency stop because I'm thinking it might burn out. It's my understanding the temp only need to be about 175. Am I wrong? Should I let it go and see what happens?

BTW, I have a very simple gcode loaded for test purposes.

Also I don't know how long ago you responded. I didn't know how to find it. Just joined. Thanks very much. Tony

Quote
MiniMfg
Yes. At this point: When I hit Start print, the extruder moves all the way to the stop on the left and stays there. Then the temp starts to rise. Every time it hits 240 degrees which I think is too high I hit the emergency stop because I'm thinking it might burn out. It's my understanding the temp only need to be about 175. Am I wrong? Should I let it go and see what happens?

BTW, I have a very simple gcode loaded for test purposes.

Also I don't know how long ago you responded. I didn't know how to find it. Just joined. Thanks very much. Tony

Have you installed Repitier-Host to control the printer. It is free to download and use. It will allow you to heat the extruder manually as well as move the print head.

Gerry

Edited 1 time(s). Last edit at 10/08/2016 07:17PM by gwc2795.

Sorry yes. I'm using repetier 1.0.6

This is the normal position for the head when heating. You haven't said whether you are referring to the temperature of the extruder or the bed, but I assume it's the extruder. The printer will not function until the bed and extruder have reached their set temperatures. The bed is normally heated first.

You need to look at the settings for bed temperature and extruder temperature in Repetier. There are both machine settings (max and default) in Repetier, plus there are specific settings for a given filament in the configuration of the Slicer.

175-195C for the extruder should do for most PLA filaments with a bed temperature of 60C. Extruder temperatures of around 240C degrees are required for printing with ABS along with a bed temperature of around 100C.

First, Thank you for taking the time!

I am referring to the extruder. The defaults in the printer section are set at 200c and 55c as specified in my instructions. There are no recommendations on the extruder settings. The instructions I have are not very good.

What do you recommend for extruder settings? I'm trying to test with pla supplied with the printer. The rec. temp for which 175.

Should I allow the extruder temp to go above 240 and just see where it stops or is there a temperature extreme I should avoid?

At this point, for all I know, if I let it go it might just move the extruder over the bed and start printing as it's supposed to.

Thanks again, Tony

Okay. Since you mentioned the bed usually heats up first I tried again and paid attention to the bed temp. It didn't move. I'm thinking at this point maybe the extruder keeps rising because it doesn't shut off until the bed is at temp. Is this thought is correct? If yes, what should I do about it?

Thanks, Tony