How to verify Transistor is working for Z Sensor

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How to verify Transistor is working for Z Sensor

Postby pbtalkAM » 2017-Apr-Wed-23-Apr

Long story short...had an accident/issue and noticed Z sensor is no longer working. No matter the direction it is connected, the light doesn't turn on anymore when near metal. Accident definitely caused huge pulling on the probe to where the tension was so high it actually disconnected *sad face* I didn't notice it until I had recovered (or so I thought) from the issue, and the print head slammed into the print bed and kept going lol.

So I've done some reading on this website to know that likely, the conductor snapped on the inside when it was pulled under high tension.

So I did more reading on this website and found that I need to be careful and determine if that transistor has been fried as well. I went to this site for a schematic and found the ground pin.
http://www.makersbox.us/2015/04/ken-ver ... -stop.html

Then I tried to measure PIN2 vs GND and I didn't get 5V.
Is something wrong? When it comes to micro-controllers, I don't want to assume because I know that maybe the voltage isn't even turned on. Can I try anything else - I can't easily hookup to the transistor to force a 12V connection to then see if there is 5V (did I just answer my own question?) that is opened. I just assumed that I should be able to probe the voltage as long as I use a common ground. the 12V connection is only needed to open the gate so current will flow.

What can I do to see if the transistor is working? I mostly don't want to order another induction probe to have it break, and, if i need to order a new printrbot board (I have rev F4 which looks like it doesn't have a current limiting resistor to prevent a short), I do it now vs in the future. FYI I have SOME electronics knowledge, but assume that I don't if any response becomes complicated :-)


EDIT before I even press "POST":
I restarted the system, and now I get 5V. So its just a probe? Geez 25 bucks, any drop in replacements from amazon? I saw other posts, but I'm not looking to upgrade or enhance, I just want a drop in replacement and don't need extra distance because I print directly to an aluminum bed.

Edit:
NM i found it on amazon, but can anyone tell me what size pin connectors these are so I can rebuild it myself? The part comes with frayed wires and I want to match the connectors from the PB Board (assuming that the board itself is perfectly fine)
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How to verify Transistor is working for Z Sensor

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Re: How to verify Transistor is working for Z Sensor

Postby Jack Crow » 2017-Apr-Mon-19-Apr

Boss,
I have the same issue, many thanks for the education on the subject.
The transistors arrived today, and I expect a replacement sensor by the end of the week.

What I would like to know is the 'why' of it all?

Also if there is a schematic of the F5 board available. Would like to learn how this whole thing works.

Thanks in advance.
Jack Crow aka Radio Mike
Virginia Beach VA
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Re: How to verify Transistor is working for Z Sensor

Postby RetireeJay » 2017-Apr-Mon-20-Apr

Jack Crow wrote:Also if there is a schematic of the F5 board available. Would like to learn how this whole thing works.

https://github.com/Printrbot/printrboard/releases/tag/revF5
After you download the zip file, unzip it. Then use Eagle software to read the file; Eagle is free for non-commercial use.
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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
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Re: How to verify Transistor is working for Z Sensor

Postby Jack Crow » 2017-Apr-Tue-06-Apr

Jay,
Thanks for the pointer. Will have to get this Eagle SW you mentioned.
Will follow up when I know more.
Thanks
Jack Crow aka Radio Mike
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Re: How to verify Transistor is working for Z Sensor

Postby Jack Crow » 2017-Apr-Tue-19-Apr

Boss,
Some follow ups.

Went and looked up the z probe by it's P/N.

L12A3-4-Z/BY

There is a page out there with a 'test circuit'.
It shows how to hook it up on the test bench. Did that.

The last time I went to tie a link to this list, I got a warning from the system, so search by the P/N and you should find it.

Dismounted the probe from the printer.

Found that BP installeda handy 3 pin connector heat shrieked to it's mate behind the hot end.
The far end of that wire connects to the printers F5 board.

Anyhow connected my 'dud' sensor as per the drawing.
The red light works fine.
It's black wire that is supposed to change state when the sensor is tripped.
Did not source voltage in either the on or off state.
Did not work as an 'open collector' type output.
The drawing was vague on that subject.
On the scope I can see a slight change in the level, but not enough to turn on any down stream transistor (FET).

Went to see about trying to fix this probe.
The only way to open this probe seems to require destroying it.
So that is out for now.

Have a new part coming from PB hopefully this week.
Have new transistors in from Digikey.

With a little bit of luck I can be back on the air this weekend.

Again, thanks all for the insight into this problem
Jack Crow
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Re: How to verify Transistor is working for Z Sensor

Postby pbtalkAM » 2017-Apr-Thu-03-Apr

Update on my end - bit the bullet (bought from PB store, but I bought more backup from amazon).

New Probe came in, doesn't work, and light doesn't turn on. I'd be surprised if I got a dud probe, now I'm thinking the Transistor was dead, and the 5V measurement literally had nothing to do with the function of the transistor. As I look at the diagram, the 5V just shows to me that the microcontroller is working to output the 5V as expected. I need to actually trigger the transistor to activate, can't verify its function statically.

Based on your advice, I will look into verifying the probe works with the Scope, and then also read about how to test a transistor (looks like lots of resources online, not too bad).

My biggest fear is that if the Transistor is dead, I need to buy a new printrboard because, unlike you, I barely have the skill to solder through-hole, let alone surface mount lol. And not just a surface mount, but a surface mount with a current limiting resistor....and a new printrboard (looks like they have rev F6) is going to run 70 dollars..

Are you going to slap a resistor on there as well so you don't run into the same issue?
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Re: How to verify Transistor is working for Z Sensor

Postby RetireeJay » 2017-Apr-Thu-06-Apr

It's unfortunate that they show an FET transistor in the schematic diagram. If you look up the part number from the Bill Of Materials, you find that the transistor that receives the signal from the probe actually is a bipolar transistor with built-in resistors. So there's really only one part to replace.

Several people posting here have said that shops that repair cellphones may be willing to do the soldering work for you if you come to them with all the appropriate parts. The transistor itself is very cheap.

The transistor, however, has nothing to do with powering-up the probe. So if you purchased a new probe and the light on the probe never comes on, it is not the fault of the transistor. I'd rather suspect that the probe is not receiving the appropriate power. Some probes run off 5V, some run off 12V. Most versions of the Rev F board have a jumper where you can select which voltage feeds the probe.
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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
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Re: How to verify Transistor is working for Z Sensor

Postby pbtalkAM » 2017-Apr-Thu-20-Apr

RetireeJay wrote:It's unfortunate that they show an FET transistor in the schematic diagram. If you look up the part number from the Bill Of Materials, you find that the transistor that receives the signal from the probe actually is a bipolar transistor with built-in resistors. So there's really only one part to replace.

Several people posting here have said that shops that repair cellphones may be willing to do the soldering work for you if you come to them with all the appropriate parts. The transistor itself is very cheap.

The transistor, however, has nothing to do with powering-up the probe. So if you purchased a new probe and the light on the probe never comes on, it is not the fault of the transistor. I'd rather suspect that the probe is not receiving the appropriate power. Some probes run off 5V, some run off 12V. Most versions of the Rev F board have a jumper where you can select which voltage feeds the probe.


Hmm I'm looking at the schematic and I see that now; however, I've never changed the jumper and its the PB drop in replacement, so why should it be different all the sudden?
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Re: How to verify Transistor is working for Z Sensor

Postby Jack Crow » 2017-Apr-Fri-20-Apr

Boss
Follow ups.
Got the transistors in.
Got the new probe in.

Installed all the new parts onto and into the Simple Metal.

No Joy.

Got a new failure mode.

Went to calibrate the probe.

Could move the Z by hand and see that the LED on the back of the probe would turn on and off in proximity to the print plate.
Went to print a test part. The X and Y do their thing.
The Z goes up and comes down, and never stops.

It rams the print nozzle into the plate until the coupling for the z axis screw pops off the motor.
Tried the old setting of -1.5, new settings of -5 and +5.
Each time it ramed into the plate after detecting.

It's late for me. Im exhausted, hungry, and aggravated.
Skipped dinner to get this thing working, and it's determined to keep failing.

In the morning Im going to do a 'buzz' check on the wires, make sure the black, brown and blue have 100% continuity back to the circuit board.
If I have to will tip this thing on it's back and see if the transistor is changing state when the sensor is tripped.

May have to get that software package and see what else is between the transistor and the uProcessor, I suspect little else is in the signal path.
If the change in state is getting to the micro I suppose I could re flash the firmware, some how I doubt that is going to help.

Worst case I order some micro's.
Damm I wanted to make stuff this weekend and it's still broken.

Jack Crow aka Radio Mike
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Re: How to verify Transistor is working for Z Sensor

Postby RetireeJay » 2017-Apr-Fri-21-Apr

Easier than tipping the bot on its back and probing with a voltmeter is to use the M119 command. It will tell you the current state of the X, Y, and Z position sensors (two switches and a probe). If you see the light on the probe change state but repeating the M119 shows no change, then the first place to check is the wiring between the probe and the board. Only then, if wiring is known good and the M119 stubbornly refuses to change, is it time to do the voltmeter thing. In very rare cases, reflashing the firmware might cure an inability to "see" the probe's state - but reflashing is usually not necessary, and runs a small risk of making things worse.

And no, there's nothing in the signal path between the transistor and the microprocessor. Not even a pull-up resistor because it's internal to the uP. You can find the schematic in PDF at reprap.org/wiki/printrboard (but it might not be for your version of the Printrboard) or download the actual schematic from Github (I posted a link to that recently in this thread).
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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
User avatar
RetireeJay
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Re: How to verify Transistor is working for Z Sensor

Postby Jack Crow » 2017-Apr-Fri-21-Apr

RJ
Thanks for the data.
This will be tasking for the morning.
Will follow up with results.
Jack Crow
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