Ran the test again under the same conditions except the K40 was powered on.
Same results and measurements as above.
You already proved the led works like we thought.
I assumed the laser was on the whole time in the first test???
Measuring the resistance while the circuit is active will give erroneous reading. Measuring voltage on Laserfire during the job and at rest would be interesting.
I was trying to replicate the test that Ray suggested here. I ran the test with the machine on and off. Same results and measurements both times.
Stand by while I perform this…
I think @raykholo went to MRRF and so has been on the road. I wouldn’t start modifying the board without him getting back on line. I know that he asks that when it comes to getting official support for his hardware that it’s too confusing to try to do it both here and on his forum, so he wants to focus his answers there. I know he’s a small business so being on the road for MRRF probably makes a dent in response time. It does sound to me like it’s been reduced to likely some hardware problem, so at this point I personally would be taking it there…
@mcdanlj my thoughts as well as far as doing any kind of modifications prior to having Ray diagnose this issue.
MRRF would explain the delay in response times if he is there… here’s to hoping he hops in soon and can help out.
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We actually have posted in both locations albeit more detail here since there was no acknowledgement on the C3D forum.
Would be great if a support entity can’t answer then provide a “out of office notification” that lets us know when they will return.
Your call @Dkwells how you want to proceed.
I am going to do some more measurement on an 817 to see if the resistance measures are fooling us.
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@donkjr can I measure voltage on Laserfire using the G pin on the board or would it be safer to use G on the LPS? (Leftmost plug, not from the LV connector)
Don’t want to short anything out here…
Oh, should we do this test with the LV connector plugged in as well as unplugged? Like we did before when trying to find voltage?
Before I was using the G on the leftmost connector on the LPS to measure voltage on the L pin, so I guess there’s my answer?
Just a reminder, electrons move from ground to positive but we often consider them moving from positive to ground, either way of thinking works. With that we know that everything but the L signal on the LPS is not connected to or with the C3D board, it’s really all stand-along stuff on the K40 machine itself so we don’t have to think about those things when considering measuring things related to the Laser Fire signal coming from the C3D board.
But the because there is the Laser Fire signal between the C3D and the LPS, we need to have a ground level in common to the two devices( C3D and LPS ). As long as you keep the LPS 4 pin connector(24V/GND/5V/L) connected between the LPS and C3D and always keep the GND wire connected between both sides, you can measure using that ground connection on either device no matter the L signal wire is connected or not.
Also, the optocoupler acts like a switch which is turned on when the LED light inside the package/chip turns on(lights up). We can’t see it light up but we can see a voltage across the 2 pins of the diode change. If you put a volt meter across any LED diode in a circuit you will see a voltage across the LED diode of anywhere from 1V to 3V(typically 2.x volts). In the circuit we’re dealing with, that switch is supposed to be connecting the GND of the C3D board to that which is connected to it which is the L signal of the LPS. When you press the laser fire button on the K40 you are doing something very similar only manual. ie YOU are the thing closing the switch to GND the L signal.
You seem able and willing to understand stuff so hopefully explaining a few concepts helps make sense of the things going on here.
@donkjr can I measure voltage on Laserfire using the G pin on the board or would it be safer to use G on the LPS? (Leftmost plug, not from the LV connector)
For this measure we want the LVPS cable plugged in. The grounds are the same in this case so use either one.
Don’t want to short anything out here…
Oh, should we do this test with the LV connector plugged in as well as unplugged? Like we did before when trying to find voltage?
If you unplug the LV cable the Laserfire will be floating (hanging without a connection) and the measurement will not be meaning full. Measuring with the cable connected is enough.
Before I was using the G on the leftmost connector on the LPS to measure voltage on the L pin, so I guess there’s my answer?
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From the C3D forum, looks like the same measurement.
Nov '19
I had tried that before and it was only 14 ohms with the power off. I think it’s shorted out. I’ll lift the pins off the board to make sure there isn’t a short on the board. Digikey is ok. … I ended up buying the kit. Delivery Wednesday.
It was closed 14 days later…
I measured a new 817 out of circuit and the collector to emitter is OPEN in either direction of the meter.
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@dougl all of that info is very helpful, thank you!! I’m all for learning new things and I appreciate your help in educating me.
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“When the red light turns on, you won’t get a full on beep from the meter, but you should have some amount of continuity something showing.
If not, bad opto.”
Correct me if I’m wrong here… when I measured G and Laserfire when running the command and the ohms dropped from ~15-17 down to ~2.5 doesn’t that indicate some amount of continuity?
Ray said if NOT, bad opto. Am I mistaken that dropping down to ~2.5 indicates some amount of continuity?
Just ran this test. Conditions were:
- K40 powered on
- LV connector plugged into LPS and C3D (24v and 5v not connected to C3D side)
- C3D powered on
- Ran command G1 X10 S0.6 F600
I measured voltage between G on LPS (leftmost connector) and Laserfire on C3D
Results:
Voltage when K40 is powered on (no command entered) ie “at rest”: ~3.3V
Voltage when running the command: Changes during the job, but drops down to ~1V then returns to ~3.3V
… about what I expected however:
It should drop to near 0** , and return to close to 5V.
This tells us the PWM signal is pulling the line low when PWM is activated but the OPTO never turns fully off (3.3v). Its off state is not high enough to keep the LPS off.
** it likely doesn’t because the signal is a PWM and the meter will measure the average.
Still feel it’s one of two things:
- The opto’s transistor is bad. My bet…
- A design problem…that I doubt. The choice of current limiting resistor value is such that when the opto part is at its highest CTR it will partially turn on the output transistor even when the processor signal is off. This means some parts will work and some may not.
At this point all you can do is replace it and see if we guessed right 
!
Is this all that I will need (other than the soldering iron obviously) to remove the opto and replace?
I have done some surface soldering in the past, but it’s been years. I’m sure I can do it, just need to be sure I have what I need.
Still debating whether to just replace the opto with one of those Amazon ones or wait for Ray to give any additional insight…
Also, any chance me replacing the opto would affect the level of support Ray will provide?
As Don said, that optocoupler just looks like it’s not doing what it is supposed to be doing. It’s supposed to be acting like a piece of wire connected to Ground and momentarily touching the L connection over and over. Pulse Width Modulation on the diode in the optocoupler does this over and over holding the “wire” on the L connection for longer or shorter periods which effect the overall laser output power.
What’s being observed is that the wire not only doesn’t “touch” the L signal well enough to bring L to the same GND potential, when it releases the connection it’s not doing that completely either.
FYI, when I was teaching some DIY IoT stuff with Arduinos and LoraWAN I’d purchased a dozen kits like this and I still use one of them when I have to do mobile repairs. It was 6 or so years ago so these look similar but not exact.
@dougl great explanation!
Anyone know if this opto would work?
https://www.digikey.com/en/products/detail/lite-on-inc/LTV-217-C-G/4573246
Current transfer ratio (min): 200% @ 5mA
Current transfer ratio (max): 400% @ 5mA
vs. the one Ray pointed out in the other thread
https://www.digikey.com/en/products/detail/lite-on-inc/LTV-217-G/4573250
Current transfer ratio (min): 50% @ 5mA
Current transfer ratio (max): 600% @ 5mA
I’m not sure what these measurements mean and how they affect this application. I’m guessing it wouldn’t work due to the range being less than what Ray suggested.