Well, if the DRV version doesn’t connect that pin, it would seem to imply that the 5V there is specifically a 5V logic supply for the stepper drivers on the normal version with the steppers on it. But do I understand that it did it not buzz out to any pin on the DRV8825s on your nano?
The V7 from 2015 (first PDF) and the V9 from 2018 (shown in dougl’s pic, the one almost everyone got nowadays) look very similar at least.
That small chip on the right of the V7 is most likely also a 78L05 voltage regulator. They are also available in this 8-pin package.
The power consumption of the V7 and the V9 are probably about the same. It doesn’t look like there were any major changes. The tweaks are likely all about saving a few cents here and there.
The CH341 should draw a lot less than 30 mA since it isn’t moving a lot of data around. According to its datasheet, 30 mA is the maximum and 12 mA is typical.
40 mA in total sounds kinda plausible. Even more so if you consider that second 5 V source via the voltage regulator. I really wonder why they did that.
Either way, 100 mA minimum for the 5 V supply seems like a sensible recommendation.
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I completed some final measurements, not because I have any interest in the Nano but to better be able to help those with M2Nano problems. [I am moving on 
]
These questions come to mind when I see K40 host connection problems and users replace their LPS with non-stock versions. Therefore I paused my other projects to see if I could get rational answers.
My conclusions are not resolved from an exhaustive trace of the PCB but from external continuity measurements that lead to logical, but potentially misleading conclusions. I have no plans to trace these boards…
Will low capacity or no 5vdc power to the Nano cause a problem?
It depends. Some nano versions derive 5vdc internally some don’t. For the ones that don’t create it internally, an external 5V must be provided. All versions that I tested had a 5vdc pin. In one case that pin was NC and the 5vdc was created by an internal LM317.
Can the Nano’s 5v be provided by the USB host?
No, all versions tested show no connection between the internal 5v buss and the USB 5V.
Can the Nano run without its 5V input?
It depends. Some nano versions provide internal 5vdc some don’t.
Is the Nano ground connected to the host USB ground?
Yes.
I have three M2Nano boards and they …wait for it…
ARE ALL POWERED DIFFERENTLY 
!
I did these checks on the three boards I have:
- 342A-28: what connects to pin 28? i.e. provides 5vdc for the logic bus.
- 5V- in: is there a 5v pin on the DC power connector?
- 5V out: what provides power to 5V on the end-stop connector (right side of the board)
- 7805: is there an internal 7805 5V regulator
- LM317: is there an alt 5V regulator
- USB to 5V: is there a connection between internal 5V and USB 5V?
- USB to Gnd: is there a connection between Nano ground and USB ground?
I tabulated these measurements below:
---- **Nano 5V power schema ----
| Model | Firmware | 341A-28 5V | 5V in | 5V endstop out | 7805 | LM317 | USB to 5V | USB to Gnd | Note |
|---|---|---|---|---|---|---|---|---|---|
| 6C6879-Laser-M2:3 | 2014.05.15 | 5V in | yes | 5V in | N | N | N | Y | 6 pin with 2x 5V-in pins |
| 6C6879-Laser-M2:7 | 2015.07.15 | 5V in | yes | 5V in | N | Y | N | Y | What is 317 for? |
| 6C6879-Laser-M2:9 | 2015.010.15 | LM317 | yes | NC | N | Y | N | Y | 2x 317, 5V is derived from 24V |
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Lol. What a mess. So, there’s a green V9 from 2018, a green V9 from 2016 (DRV), and a blue V9 from 2015. And the blue and green non-DRV V9 versions aren’t even the same.
I wonder if at least the “firmware ver” date can uniquely identify them.
I thought I had the same green 2018 V9 as the one in dougl’s pic, but nope, mine’s not a 2018.06.18 V9, it’s a 2018.01.08 V9.
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Just to add more data, my M2 Nano is a green board 6C6879-Laser-M2:9 with 2016 firmware and the layout appears to match Don’s 6C6879-Laser-M2:9 with the 2015 firmware. 5V derived from the 24V.
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If yours is like mine & the 5V-in pin is not connected to anything?
Theoretically you could disconnect that 5V connection from the LPS and is would still work!?
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Yea the 5v isn’t connected to anything on mine either. I’ll try disconnecting the 5V to verify.
LOL … An M2:9 only with a 7805 and no 5v to the end-stops. Clearly the model # does not capture the hardware version!!!
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On my board, when I powered from 24V in, I measured 4.? volts on the end stop pins so there some some thing there even if pullups through the uCPU.
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The community could benefit from tracing this board to a schematic.
That’s not on my list… especially now that there are so many versions… and I do not use it…
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Boy, it seems the controller is made the same way the K40 machines are, ie same name and shape but everything else is up for grabs as to what’s inside.
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So what I’m hearing is that if anything ever happens to my M2 I should just ditch it and put in some more standardized controller? 
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That’s why I use smoothies. Support, schematics, docs, open code, updates, rational engineering …
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The nano boards are probably 4 layer boards so that’s why you can’t see the 5v connection to the a4988 step drivers.
Could be 4 layer but I used a meter to test for 5V many places on the board especially where the 5V connects to the processor chips and found no continuity.
This made me curious since the A4988 needs 5V see A4988: DMOS Microstepping Driver with Translator
So I measured myself and indeed no 5V connection to the 5V input. However 24Vdc goes to a 78L05 on my board (like doug’s photo post). So there we have it. I never understand the logic of chinese designs.
ps. (Just pulled a Chinese TCL led tv apart after it’s backlite power supply was failing. The voltage for the pwm control IC (of the backlight) sits behind the transformer which it drives. How does the pwm IC gets it’s power from?)
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Turns out it depends on the board version some use the 5V pin some don’t 
And some use a LM317 vs 7805… go figure!
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What do you have lugged in on the far left? It says X-motor, just asking because I do not have anything plugged in there…
If the flexible flat cable is used, the X motor connector and the end stop connector are unused. The FFC handles these two things.
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