Defective generator, problem Nano V2

Hello world,

I have not used my Nano for 2 days. It remained in its cases and this morning I wanted to make a demonstration of my DSO Nano V2 with a friend. By connecting the generator and the probe (I did not connect the mass together like BenF says it) to visualize the square waves, here now what I have

I reloaded it and that does not change anything. What occurs? The remainder functions correctly. If I connect the generator with high speakers, I hear the sound of the frequencies when I pass from one frequency to the other. But as you can see on the image, there is a problem.

I hope that it is not already broken!


Try changing VD to 1v/Div and TD to 500us/Div.

And try Push and Hold OK button.

Here the result:


Yah something is not right. It’s not getting a good signal. If you have a multi meter test the resistance of the probes and gen leads. Maybe generator leads went bad, shorted or brocken.

Other than that I can’t think of anything else. I hope others will shine in with advice.


R25 resistance posts on my ohmmeter “14.09K or 8.59K” and R26 posts “13.07K or 44.13K”. The value changes by reversing the probes of my ohmmeter. Obviously there is a problem with these resistances.


Are you measuring resistors on the board in circuit? Most times you have to remove resistors, caps, transistors even diodes to accurately measure them because they interfere with one another while in circuit.

What I was saying in previous post is take the probes out from nano and see the resistance of probes.

Sorry to answer also tardily.

The probes are OK, they posts 4ohm with my ohmmeter. I also compared with other probes similar, and I always obtain 4ohm. My voltmeter posts 87mV on the output of generator, it does not matter the probe used.

I as noticed as the battery discharges more quickly than front.

I cannot unsolder resistances because it is of micro component then impossible to change.

I am disappointed to note the brittleness of this oscilloscope.

Thank you.

Hi. First grab the v2 schematic … Scheme.pdf
And datasheet … HC125.html

What board version of V2 do you have?

You should forget about R25, R26. These are related to USB not Func Generator.

Lets make sure your 74HC125 has VCC on pin 14. Should be close to Battery voltage. Mine has 3.7v

And pin 8 about half of Battery voltage. Mine has 1.9v.

Attached pics of my Nano 2.5. I placed Ground Volt meter probe on USB shield and Red to VCC of 74HC125 pin 14 then 8.

Be careful.


My board version: DSO201V2.5

I placed Ground Volt meter probe on USB shield and Red to VCC of 74HC125 pin 14 then 8

Fuction Gen Out=0.8v

Pin 8=0.8v
Pin 14=3.7v

Thank’s for help me.

Ok lets check more points.

With my battery at 3.7v I get these readings in attached pic. My DVM Ground is on USB Shield as before.

Also lets see if Main Arm processor U6 putting out a signal.


If you short out this signal, you will have have replace U6. So for safety do what I did in Pic.

Take some electrical tape and make a slit. Put it over U9 exposing only pin 9. Don’t ever short pin 9 with pin 10 of U9.

Get DSO Nano positive probe. Put a needle or solid wire in it. I put TR Mode to SING to capture the signal. I used a mirror in front of me so I could see Nano screen. Put positive probe on pin 9. You should see the signal as in Pics.

If you do see signal, then post likelly your U9 is dead.

may be better to him to measure some AAA, AA battery, because it is not evident that his oscilloscope part is working well. may be his input is damaged?
can his device show 1.5v on some battery? or test it with some audio jack, measuring voltage there?

ps…measuring the processor with some voltmeter, is a good way to damage it. imho. processor pin is working - he watches generator signal, and listens(!!!) it via speakers(I doubt he can listen signal if processor doesnt deliver it). but he cant see signal properly on the screen(it is too small).

advice. to have less troubles with measurements on such small elements, bind with scotch tape a sharp needle to the probe, and use needle to touch testing points.

Ok I took the measurements of tensions:

EN85 pin 1=+3.7v

For Pin 9(U9), I did not have any signal with the screen and after 15 seconds, the U9 becomes very hot.

When I connect my speakers of my computers in the output of the generator, I to hear the various frequencies.


Looks good.

Wow, my U9 is cold, never seen it even get warm. I am guessing its shorted inside or Gen Output is shorted. The fact that you can’t see any signal on Pin 9 (Fout*) of U9 is not good. Either U9 pulling/shorting it ground or STM32 is shot.

alys: thank you.

gtr: As alys said. Hook up some working battery (AAA, AA, 9v, CR2032…) to Nano Input and adjust VD to see a straight line and proper reading. This will verify if Input is working or not.

I think you somehow need to disconnect U9. Perhaps lift pin 14 VCC. I don’t like that is hot.

FYI: I know V2 battery soldered directly :blush: So its best to splice in some connector before you do resistance checks or soldering to avoid shorts.

imho, working plan.(i have not device, and see only schematics and photos)

  1. discharge yourself touching with finger some ground point of your device. device must be turned off.
  2. put your finger on the chip which was hot (U9?), turn device on and wait, if it will be warm or hot. is warm/hot - turn device off and visually search for shortening from U9 output pins and device generator output jack. if it is hot - it is problem. may be problem is in jack(remove any cable from this jack-cable can be shortened too).
  3. if U9 is not warm or hot(without cable in generator output jack and with) - try to measure some battery with this oscilloscope, to prove that oscill. part is working. if you cant measure proper volts - oscill part is not working, but generator seems good. results here.

PS. looking at the scheme, i see that they have not any resistor in serial to limit output current of u9. so if output is shortened - it can damage u9? Also, it is obviously wrong to drive some speaker with generator output. there must be resistance about 100 or greater omhs in serial, to limit output current. I propose to make this mod to everybody to save U9 output.

The U9 is hot with or without cable connected to the input or output of the generator. I can test the batteries, no problems. I can test the AC as well and I see a sine wave. I have a multimeter with a square wave function and I can see it but look at the images on different V / div, the top and bottom of the wave is not perfectly straight.


because U9 is hot(it consumes big current) - it is damaged or some outputs are shortened to the ground, to another output or somewhere. if output is not shortened then chip u9 has been internally damaged and shortage is internal. also as i said - there must be resistors in serial from u9 to output jack.
ripple on graphs may have the reason, that u9 is shortened. device withstands high current, and this is the ripple with his generator frequency.
so. inspect where is shortage, with turned off device, anyway you cant have it turned on - u9 will burn down.

ps. do not try to drive speakers with device generator.
pss. nothing in this device could be hot. it is low current device, and all parts must be at (about) ambient temperature.

I don"t know much about electronics but is 74HC125 chip a 4 in 1 fast switches? I don’t know its purpose or why it was used in design.

Anyways, looking at schematic and datasheet I see An are Inputs, Yn are Outputs and Cn are On/Off pins. When Cn is grounded, then connection is made from An to Yn.

If this is true, than A8, Y9 and C9 are of interest. The other 2 sets used for unknown connector? And 1 set is Xed, possibly not used at all?

I am nor sure about all this so need experts to help.

If it was me. What I would do is carefully lift pins 8, 9, and 10th.
Feel U9 if it still get hot. If still hot. Then lift pins Sets for TX and RX . Again feel if its hot. Then if its still hot, then last set is shorted to or the whole U9 is damaged which you have to replace anyways. Now I would remove U9 and do the Will it Blend test.

Once removed, then test pad 9 for signal like I showed before.

However if removing first set removes the short perhaps you can salvage U9 by re routing to unused set of pins.

Again I speak from limited knowledge so please run it by another person at least.

I wish you best and keep us informed.


it is bus driver. the common usage - to attach/detach some signals from one part of device to another one or to/from external device. and to raise output current abilities of some low current outputs and to isolate expensive chip(like processor here) from output jack(better to ruin cheap bus driver than main processor). Ax - inputs, Yx - outputs, Cx - on/off pins. if Cx is in off state(high level on Cx) - Yx is in high impedance state and element is detached from output.

all output pins are of interest, if chip gets hot. because is some output isnt in high impedance state and is shortened somewhere - all chip will be hot. so all Y pins must be checked if they are not in high impedance.

from schematics we see that 3th element - has input (A3) connected to processor pin Fout*, C3 connected to the ground, and Y3 goes to jack. seems low C3 enables element and it simply repeats signal from Fout*, driving jack.
seems all Cx of the chip are grounded, so all elements are enabled. so any shortage on Yx, if appropriate Ax is high(seems it is not inverter), can get hot the chip. so it is good to measure voltage on Ax. if it is high(more than 1 v) but Yx is low(zero volts) - it is wrong.

imho, if his oscilloscope part is still working, better to do next - switch off generator(if it can be programmatically switched off), look via oscilloscope probe or voltmeter, if Ax is high, but Yx is low.

imho, because schematics has not 100-150 omh resistor from Y3 to output jack he could overload Y3 with speakers(as he said) and damage Y3 output.


Alys, thank you for taking your time with great explanation.

Looks like it works ok. As far as I know, Function Generator is on at all times. Only way to disable it is to edit firmware source, recompile, then flash.

Interesting advice. I would do it if it was easy. I have not took the main board out yet to look at the Output connector so not sure how easy it is.
I also read another safety feature to add is a Diode to protect against grounding the Output. Few burned out their 74HC125 by connecting Fout to Input ground.

The least gtr should do is lift pin 14, 9, 6 and 2 if he doesn’t want to troubleshoot which should remove the short and not cause further damage.