DSO138
« on: March 16, 2018, 11:40:03 AM »
One of these arrived a few days ago ,I had checked other reviews online and wasnt hopping for much ,

Cost 12 dollars ,presoldered and ready to go out of the packet .
I found a grounding mod which did help a bit with noise
but  I also replaced the caps on the V+ rail with branded low impedence items ,still a bit noisey ,left the unit on over night.....
This morning it was alot quieter and Im typically able to get a noise reading of less than one millivolt pp on the 10mV per division range ,  there was short term spikes of almost 10mV pp before I did any of the mods ,of course this was with the input grounded Im just doing a few more tests now ,but over all the waveform looks a lot cleaner with less wobble than before.
Im going to put a rotary encoder on to make adjustment faster ,but its all seems to work fine and the interface is simple .
Ok bandwidth starts to fade at around 40khz and the screen is no bigger than a couple of postage stamps , but for a simple quick tester for audio its great, well worth spending the extra on better electrolytics too, I'll post a few pics later of the mods and comparisons between noise  before and after.


ruffrecords

Re: DSO138
« Reply #1 on: March 16, 2018, 11:55:23 AM »
I had to laugh when I visited the JYE tech web site:

https://www.jyetech.com/Products/LcdScope/e138.php

Top of the page this Chinese company is complaining about some other company stealing its design!!

Cheers

Ian

www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: DSO138
« Reply #2 on: March 16, 2018, 12:01:06 PM »
heres a pic of what was going on with an unmodded one

Re: DSO138
« Reply #3 on: March 16, 2018, 12:02:55 PM »
With the same settings on mine I only have noise one pixel high ,certain ranges are just a flatline with no visible noise at all ,
This thing is actually half useable , I still seem to be getting some noise in the negative direction ,seems a bit variable ,I wonder if thats because I havent changed the neg rail caps yet , Im pleasently surprised with this little toy .
« Last Edit: March 16, 2018, 12:31:48 PM by Tubetec »

Re: DSO138
« Reply #4 on: March 16, 2018, 12:51:53 PM »
Theres an anoying Jtetech logo that keeps flashing up on the screen while in use and a splash screen/anti piracy warning on boot up that can be removed by loading third party firmware ,The neat thing is that the open source firmware provides the abillity to access a second analog input and a pair of logic channels as well , volts per division on the second analog input is fixed as the range switching is only active on channel one ,but with an external attenuator and line input it should work ok .According to the schematic I need a voltage of 1.6 volts at the analog input so the wave form offset on the screen is correct , input one uses the offset at the output of one section of a TL084 ,  I think theres a vertical offset adjustment per channel in the UI at any rate .

https://github.com/ardyesp/DLO-138

Rob Flinn

Re: DSO138
« Reply #5 on: April 11, 2018, 04:39:48 AM »
With the same settings on mine I only have noise one pixel high ,certain ranges are just a flatline with no visible noise at all ,
This thing is actually half useable , I still seem to be getting some noise in the negative direction ,seems a bit variable ,I wonder if thats because I havent changed the neg rail caps yet , Im pleasently surprised with this little toy .

Is ths with the scope input shorted ?    It might be noise it's picking up externally.
regards Rob

Re: DSO138
« Reply #6 on: April 11, 2018, 07:14:07 AM »
Hi Rob,
I made good progress on reducing the noise in the dso, unfortuately  now the STM32 seems to have developed a short to ground across the 3.3V rail,either that or the board developed the short internally  , I have a spare processor on the way .

The 3.3V rail is derived from the 5 volt op amp supply which seemed to be a major source of noise ,another mod I found sourced the 3.3v directly off the 9 volts supply ,but I didn't get a chance to try that out yet . Definately some extra screening both to prevent external noise and internally to prevent rf getting into the analog path is a good plan though. Anyway win some loose some ,not a massive amount of cash involved in any case .

gyraf

Re: DSO138
« Reply #7 on: April 18, 2018, 03:13:56 AM »
(..thanks for the updates, following from sideline...)
..note to self: don't let Harman run your company..