ESD

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ESD

Postby davegun » 2015-Jan-Thu-22-Jan

My Z Probe when out on my Simple 1405 (wood). I looks like the MOSFET on printrboad Z Stop has failed. I have been in contact with printrbot support and it looks like they are sending me a replacement board. Today I put an ohm meter on the power ground and I am not seeing any connection between ground and the z-probe threaded case, or the case of the stepper motors. I'm wondering if a static discharge to the Z probe, or stepper motors could take out something on the printrboard?

Since the 1405 is all wood, there is no grounding though the case, I'm thinking about adding some ground wires to all the metal parts to give any static discharge a path to ground (not thought the electronics). Has anyone else experienced this, or has tried grounding?

Thanks,

Dave
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Re: ESD

Postby thawkins » 2015-Jan-Thu-23-Jan

davegun wrote:My Z Probe when out on my Simple 1405 (wood). I looks like the MOSFET on printrboad Z Stop has failed. I have been in contact with printrbot support and it looks like they are sending me a replacement board. Today I put an ohm meter on the power ground and I am not seeing any connection between ground and the z-probe threaded case, or the case of the stepper motors. I'm wondering if a static discharge to the Z probe, or stepper motors could take out something on the printrboard?

Since the 1405 is all wood, there is no grounding though the case, I'm thinking about adding some ground wires to all the metal parts to give any static discharge a path to ground (not thought the electronics). Has anyone else experienced this, or has tried grounding?

Thanks,

Dave


Hmmm. There is no mosfet on the zstop. Its an input not an output.
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Re: ESD

Postby thawkins » 2015-Jan-Fri-00-Jan

thawkins wrote:
davegun wrote:My Z Probe when out on my Simple 1405 (wood). I looks like the MOSFET on printrboad Z Stop has failed. I have been in contact with printrbot support and it looks like they are sending me a replacement board. Today I put an ohm meter on the power ground and I am not seeing any connection between ground and the z-probe threaded case, or the case of the stepper motors. I'm wondering if a static discharge to the Z probe, or stepper motors could take out something on the printrboard?

Since the 1405 is all wood, there is no grounding though the case, I'm thinking about adding some ground wires to all the metal parts to give any static discharge a path to ground (not thought the electronics). Has anyone else experienced this, or has tried grounding?

Thanks,

Dave


Hmmm. There is no mosfet on the zstop. Its an input not an output.


I take that back, apparently there is an "revf4" varient, different to the "revf" which does have a small mosfet on the z stop input. It appears to be being used as a level changer to enforce the 4.8v input range on the zstop input to the AVR, interesting. That is the board with the 5v/12v jumper for zstop sensor power selection.
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Re: ESD

Postby davegun » 2015-Jan-Fri-03-Jan

Yes, I have the Rev F4 board. I'm not sure what caused this, it worked well for about a week, then the Z-stop quit working.

I live in the northern US and it's been quite cold. My furnace has been running steady for the past several days and the humidity is low. It's easy to build up some static in these conditions.

Thanks,
Dave
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Re: ESD

Postby thawkins » 2015-Jan-Fri-04-Jan

davegun wrote:Yes, I have the Rev F4 board. I'm not sure what caused this, it worked well for about a week, then the Z-stop quit working.

I live in the northern US and it's been quite cold. My furnace has been running steady for the past several days and the humidity is low. It's easy to build up some static in these conditions.

Thanks,
Dave


Normaly there is a high value resistance between the mosfet gate and ground, a few hundred k or so, to bleed any static charge away, but they seem to just have a naked gate input here. The esd protection resistor may be incorporated in the fet package, but it does not appear in the schematic. Disconnected Mosfet gates are normaly very static sensative.
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Re: ESD

Postby RetireeJay » 2015-Jan-Fri-11-Jan

As an Electronics Engineer, I would call the use of a MOSFET with a naked gate connected to the outside world a design flaw for sure. For the optimum protection of the MOSFET, there should be a resistor to ground (or to +5V, depending on the nature of the external circuit driving it), and this resistor should have a relatively low value, like 4.7K.
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Re: ESD

Postby davegun » 2015-Jan-Fri-22-Jan

RetireeJay wrote:As an Electronics Engineer, I would call the use of a MOSFET with a naked gate connected to the outside world a design flaw for sure. For the optimum protection of the MOSFET, there should be a resistor to ground (or to +5V, depending on the nature of the external circuit driving it), and this resistor should have a relatively low value, like 4.7K.


Great information! I'm an Electrical Engineer, but my experience is in building design and construction, not designing circuits. Tinkering with electronics is just a hobby:) I made a short jumper that has a 10K resistor from the sensor output to ground. I will test it out when I get a working board.

Do you think grounding the exposed metal of the probe, and maybe run the sensor wires through a ferrite choke would help ?

Thanks,
Dave
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Re: ESD

Postby thawkins » 2015-Jan-Fri-22-Jan

davegun wrote:
RetireeJay wrote:As an Electronics Engineer, I would call the use of a MOSFET with a naked gate connected to the outside world a design flaw for sure. For the optimum protection of the MOSFET, there should be a resistor to ground (or to +5V, depending on the nature of the external circuit driving it), and this resistor should have a relatively low value, like 4.7K.


Great information! I'm an Electrical Engineer, but my experience is in building design and construction, not designing circuits. Tinkering with electronics is just a hobby:) I made a short jumper that has a 10K resistor from the sensor output to ground. I will test it out when I get a working board.

Do you think grounding the exposed metal of the probe, and maybe run the sensor wires through a ferrite choke would help ?

Thanks,
Dave


The reason why i suggested a much higher resistance, was that the probe has an internal load resistance of 4.7k between the output and the vcc supply. So using a 10k resistor to grnd on the gate input is going to form a voltage divider that will put 8v on that input when the probe is powered from 12v. The probes LED is also across that load with a series 2.2k resistor, so the 4 volts across the load when it turns off is going to be enough to keep the led on permenantly.

While i agree that a lower value is safer, 100k will provide enough to bleed off static charge without creating a large drop across the load in the off state.

A better way alltogether is to not have a mosfet at all and use a diode with the cathode connected to the probe output, and the other end connected to the mcu input, that ensures that the probe behaves like an open collector ouput, and the effect of the internal load is elminated and the probe can only sink current, not source it, the internal pullup on the mcu will provide the clamping to 5v when the probe is in the off state, regardless of what voltage the probe is operating with..

However im not 100% certain if the printrbot supplied probe IS NPN or PNP. mine are all NPN which is the most common type, and above holds true, but mine are not printrbot supplied. Ie does the ouput go low when activated NPN or go high PNP.
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Re: ESD

Postby RetireeJay » 2015-Jan-Sat-08-Jan

+1 on thawkins.
I don't have a probe, and I don't know the exact specs of its output. The selection of resistors is totally dependent on the complete circuit. So he's right, my suggested 4.7k isn't going to work.

I didn't realize there was a voltage discrepancy where the probe puts out 12V in the high state. Ouch. I guess the MOSFET has at least a 12V rating on its gate...

As to using a diode in series with the signal lead (and I assume no MOSFET buffer), it would be worth checking the definition of a logic LOW at the input of the MCU. Back in the TTL days, logic LOW was 0.4V, and you can't get there if you have a 0.6V diode in series with your "ground." But maybe nowadays logic LOW is defined as some other voltage south of 2.5V (there's always a "forbidden zone" between a clean logic LOW and a clean logic HIGH).
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Re: ESD

Postby thawkins » 2015-Jan-Sat-08-Jan

RetireeJay wrote:+1 on thawkins.
I don't have a probe, and I don't know the exact specs of its output. The selection of resistors is totally dependent on the complete circuit. So he's right, my suggested 4.7k isn't going to work.

I didn't realize there was a voltage discrepancy where the probe puts out 12V in the high state. Ouch. I guess the MOSFET has at least a 12V rating on its gate...

As to using a diode in series with the signal lead (and I assume no MOSFET buffer), it would be worth checking the definition of a logic LOW at the input of the MCU. Back in the TTL days, logic LOW was 0.4V, and you can't get there if you have a 0.6V diode in series with your "ground." But maybe nowadays logic LOW is defined as some other voltage south of 2.5V (there's always a "forbidden zone" between a clean logic LOW and a clean logic HIGH).


I have an IN4001 on my two probes which operate at 12v, and they work very well.
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Re: ESD

Postby davegun » 2015-Jan-Sat-21-Jan

I looked up the part number on the probe, it LJ12A3-4-Z/BY. It's a PNP, 6-36VDC 4mm Detecting Distance NO Inductive Proximity Switch. I also tested my probe and the LED works correctly, but the output with a 12V supply is 6V, and when triggered is 4V, so I think this is also bad. They were $5 on Amazon so I ordered two.

I like the diode with no MOSFET, if I were not getting a replacement board, this looks like the best solution I have seen. The MOSFET could be removed from the board, or I could reassign an open pin from the Extension Pin Header. I would need to re-compile and flash the board. I have poked around in the source code and found how to change the pin numbers, but I don't think I'm quite ready to go there just yet.

I can print just fine with a level bed, and no Z stop. To be honest, I have made the best prints since the Z Probe went out. I have only been printing for a few weeks, so that may not be saying much:) I think for now, if Printrbot follows through and replaces my board, I will run it stock, but with added grounding. Grounding the probe case to give any static discharge a path to ground, and a choke on the Z Probe wires to discourage any static discharge (or induced current) from traveling down the probe wires can't hurt. If the MOSFET get's taken out again, I will make it work another way.

Thanks for all the discussion, this has been interesting and information I can use!

Dave
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Re: ESD

Postby Hopbot » 2015-Jan-Sun-00-Jan

Dave,
Just so you know you are not alone with the blown MOSFET. I like the idea of adding grounding wires, I could work on adding them while my new board in coming. I haven't got to print anything yet, the PB guys wanted me to send in my board before they sent out a new one. I also ordered a couple new proxes for the Z stop, it is amazing that they ship two of those from China on a plane for $10 somebody is losing money on that deal for sure.

Thanks to all for the information from me too!

Chris
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Re: ESD

Postby thawkins » 2015-Jan-Sun-01-Jan

davegun wrote:I looked up the part number on the probe, it LJ12A3-4-Z/BY. It's a PNP, 6-36VDC 4mm Detecting Distance NO Inductive Proximity Switch. I also tested my probe and the LED works correctly, but the output with a 12V supply is 6V, and when triggered is 4V, so I think this is also bad. They were $5 on Amazon so I ordered two.

I like the diode with no MOSFET, if I were not getting a replacement board, this looks like the best solution I have seen. The MOSFET could be removed from the board, or I could reassign an open pin from the Extension Pin Header. I would need to re-compile and flash the board. I have poked around in the source code and found how to change the pin numbers, but I don't think I'm quite ready to go there just yet.

I can print just fine with a level bed, and no Z stop. To be honest, I have made the best prints since the Z Probe went out. I have only been printing for a few weeks, so that may not be saying much:) I think for now, if Printrbot follows through and replaces my board, I will run it stock, but with added grounding. Grounding the probe case to give any static discharge a path to ground, and a choke on the Z Probe wires to discourage any static discharge (or induced current) from traveling down the probe wires can't hurt. If the MOSFET get's taken out again, I will make it work another way.

Thanks for all the discussion, this has been interesting and information I can use!

Dave


If the probe is PNP, then the situation is slightly different as the internal load resistor for the probe is between output and ground and not vcc, so a 10k resistor between the input and ground would work fine as a static charge bleeding measure. And would ensure the gate was grounded when the probe was disconected. Given the rate at which the wire faults in the probe wire show up, that is a real problem. The situation i described was for an NPN probe which is what i have.
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Re: ESD

Postby thawkins » 2015-Jan-Sun-01-Jan

davegun wrote:I looked up the part number on the probe, it LJ12A3-4-Z/BY. It's a PNP, 6-36VDC 4mm Detecting Distance NO Inductive Proximity Switch. I also tested my probe and the LED works correctly, but the output with a 12V supply is 6V, and when triggered is 4V, so I think this is also bad. They were $5 on Amazon so I ordered two.

I like the diode with no MOSFET, if I were not getting a replacement board, this looks like the best solution I have seen. The MOSFET could be removed from the board, or I could reassign an open pin from the Extension Pin Header. I would need to re-compile and flash the board. I have poked around in the source code and found how to change the pin numbers, but I don't think I'm quite ready to go there just yet.

I can print just fine with a level bed, and no Z stop. To be honest, I have made the best prints since the Z Probe went out. I have only been printing for a few weeks, so that may not be saying much:) I think for now, if Printrbot follows through and replaces my board, I will run it stock, but with added grounding. Grounding the probe case to give any static discharge a path to ground, and a choke on the Z Probe wires to discourage any static discharge (or induced current) from traveling down the probe wires can't hurt. If the MOSFET get's taken out again, I will make it work another way.

Thanks for all the discussion, this has been interesting and information I can use!

Dave


If the probe is PNP, then the situation is slightly different as the internal load resistor for the probe is between output and ground and not vcc, so a 10k resistor between the input and ground would work fine as a static charge bleeding measure. And would ensure the gate was grounded when the probe was disconected. Given the rate at which the wire faults in the probe wire show up, that is a real problem. The situation i described was for an NPN probe which is what i have.
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Re: ESD

Postby davegun » 2015-Jan-Sun-18-Jan

thawkins wrote:If the probe is PNP, then the situation is slightly different as the internal load resistor for the probe is between output and ground and not vcc, so a 10k resistor between the input and ground would work fine as a static charge bleeding measure. And would ensure the gate was grounded when the probe was disconected. Given the rate at which the wire faults in the probe wire show up, that is a real problem. The situation i described was for an NPN probe which is what i have.


That makes sense.

Thanks,

Dave
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Last edited by Mooselake on 2015-Jan-Mon-14-Jan, edited 1 time in total.
Reason: Fixed quote typo for you :)
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Re: ESD

Postby davegun » 2015-Jan-Sun-19-Jan

Hopbot wrote:Dave,
Just so you know you are not alone with the blown MOSFET. I like the idea of adding grounding wires, I could work on adding them while my new board in coming. I haven't got to print anything yet, the PB guys wanted me to send in my board before they sent out a new one. I also ordered a couple new proxes for the Z stop, it is amazing that they ship two of those from China on a plane for $10 somebody is losing money on that deal for sure.

Thanks to all for the information from me too!

Chris


Chris,

Good luck! It's too bad they made you send the board back first, it isn't that hard to print without the Z Probe.

Dave
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Re: ESD

Postby lwalkera » 2015-Jan-Mon-13-Jan

Yeah, it's an issue. Brook wanted something quick to use 12V on the probe towards the end of the Rev F dev cycle, since some of the probes they were getting didn't work correctly on 5V. So I just used the same FET as the fan output since it was already on the BoM. Live and learn I guess.

On new boards, I told them to switch to MMUN2211LT3GOSTR-ND which is a pre-biased NPN BJT. It shouldn't be as sensitive to ESD, and is a drop in replacement if you'd like to repair your board.
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Re: ESD

Postby davegun » 2015-Jan-Mon-20-Jan

lwalkera wrote:Yeah, it's an issue. Brook wanted something quick to use 12V on the probe towards the end of the Rev F dev cycle, since some of the probes they were getting didn't work correctly on 5V. So I just used the same FET as the fan output since it was already on the BoM. Live and learn I guess.

On new boards, I told them to switch to MMUN2211LT3GOSTR-ND which is a pre-biased NPN BJT. It shouldn't be as sensitive to ESD, and is a drop in replacement if you'd like to repair your board.


The BOM for the F4 shows Q4 is the MMUN2211LT3GOSTR-ND. I looked it up on Digi-Key and minimum order is 3000. The MMUN2211LT3GOSCT-ND minimum order is one. I assume the only difference is one is a tape and reel that are used in mass production, the other isn't. I have never ordered anything from Digi-Key, do they take small orders? If so, I will order a fist full just to have some spares in case it happens again.

Dave
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Re: ESD

Postby lwalkera » 2015-Jan-Mon-22-Jan

Yeah, those are the same part, just different packaging. I bought a strip of 100 myself for testing and rework because they were so cheap. Also, if you're in the US, make sure you use the First Class Mail as the shipping option. I got mine delivered (in CA) about 2 days after it left the warehouse (from MN).
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Re: ESD

Postby davegun » 2015-Jan-Tue-22-Jan

Laine,

Great info, thanks. I think I will order some.

Dave
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Re: ESD

Postby davegun » 2015-Jan-Thu-23-Jan

Update, Today my two Z Probes came in the mail, my MOSFETs from Digikey came in the mail, and Printrbot sent me a message that my replacement board is in the mail! I should have this problem covered.

Dave
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Re: ESD

Postby davegun » 2015-Jan-Sun-23-Jan

Final Update: My replacement printrboard came this weekend. When replacing the board, I installed a new Z Probe. I looped the three sensor wires once through a ferrite toroid. I soldered a ground wire on one of the lock washers and used this to ground the probe. I looped the ground wire around case bolt of the extruder stepper and ran the ground in the spiral wrap. I ground the y stepper, and the z stepper on the way. The ground wire is terminated at the power supply ground. I also added a jumper with resistors in line with the Z Probe.

Everything now works as it should. I don't plan to test this by touching it after running across the carpet in wool socks, so all this extra voodoo may not do much, but it makes me feel better :)

Thanks everyone for your comments. I'm new and don't know who's who, but I couldn't help noticing Laine Walkers name on the printrboard... small world!

Thanks,
Dave
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Re: ESD

Postby JonS » 2015-Apr-Sat-14-Apr

My z probe has failed. The wiring was flaky, so the probe was failing on the right side of the bed. I spliced in some replacement wires, but now it's completely dead. So I wonder if my FET has blown too, or if my manipulation of the cable has opened up another break somewhere.

I have a new probe on its way, so I'll find out soon. I guess I should order some FETs just in case.

I see they're made by ON Semiconductor, my company. Not that that really helps me. I work for the CMOS image sensor division.
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Re: ESD

Postby RetireeJay » 2015-Apr-Sat-14-Apr

The FET was a mistake to begin with. Laine Walker-Avina (lwalkera) designed the board, and he's admitted as much. He also has a redesign used in boards Rev F5 and above using a bipolar transistor with built-in biasing and protection resistors. It's a physical drop-in replacement for the FET. viewtopic.php?f=15&t=8929&p=57547&hilit=bjt#p57547

So don't go buying replacement FET's; buy the bipolar one instead.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
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"My next printer is..." Prusa i3 MK3, upgraded to MK3S
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Re: ESD

Postby JonS » 2015-Apr-Sat-20-Apr

Thanks Jay. That's what I've bought.

Yes, it was a mistake to use an unprotected FET. I know ON Semiconductor has a whole load of ESD protection parts in its portfolio. Maybe I can put lwalkera in touch with one of our Solution Engineering Centers. I'd love to see us doing something for 3D printers, and we have a lot of parts in our portfolio (including stepper motor drivers) that are a fit.
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Re: ESD

Postby scotthraban » 2019-Jan-Tue-13-Jan

I know this is a really old post, but hoping those in the know can still help. I am pretty sure that the fet on my board is fried. I am getting the "up, then up some more when homing Z", always triggered according to M119, but light only comes on when near the bed / metal. I see the voltage change along with the sensor light when measured at the board Z stop connector, so pretty sure it is not the sensor, but have one on order anyway, since that is the easy fix.

I also have some of the bipolar ... transistors identified above on order for when changing the sensor does not work ;). That is where I need help, does anyone have a picture or description of where the original fet is on the F4 board? I see a component just off the corner of the Z stop connector that looks to be the right form factor, but it is not labeled that I can see ...

Thanks in advance,
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Re: ESD

Postby RetireeJay » 2019-Jan-Tue-14-Jan

Yes, there is a 3-terminal device, Q4, immediately adjacent to the Z probe connector; that's the "MOSFET" or input transistor for sense level translation.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
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RetireeJay
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Re: ESD

Postby scotthraban » 2019-Jan-Sat-15-Jan

Thanks @RetireeJay, I also found the schematic of the board, and proved to myself with a multimeter that I had idetified the right component.

First time doing any SMD soldering, so I tried to practice on an old dead board, but I think the board may have been too old and didn't have lead free solder, since it was much easier to remove components than from the F4 board, and unfortunately I ended up lifting a pad. As a silver lining, the pad I lifted was for the sensor trace, so I was able to do a wire patch from the connector to the leg of the transistor, bypassing the trace.

So my board now looks like ... crap ..., but it WORKS! Thanks so much to everyone on this thread, you get extra karma points today!

--Scott
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