Hi,
I bought a assembled DSO138 from aliexpress seller here: https://www.aliexpress.com/item/DSO138- ... 0.0.wVDyay
It has been working great for about a month but all of a sudden it just died on me. Screen is white and no LED blinking on reset or startup. The LM78L05 is burning hot and it
turns out the 3.3V rail is shorted. I see nothing looking bad on the board:
https://photos.app.goo.gl/Wdj09VRALS2BpJCV2
What are my options? I read something about disconnecting a jumper (J4?) to see if it's the MCU that's burnt or something else. What should be my next step? Any help highly appreciated!
(I have ordered another one but delivery time to Sweden is going to be at least a month and I really need it to debug some other projects)
Working, but broke, 3.3V shorted.
Re: Working, but broke, 3.3V shorted.
I desoldered the JP4 jumper and now I have 3.3V on TP-22. Does this mean my MCU is fried? I don't think I stand a chance of changing that one I'm afraid. I have bought a hot air soldering station but I'm totally noob on smd.
Re: Working, but broke, 3.3V shorted.
I assume you have removed the LCD screen so you know it's not at fault.
If you are very lucky the problem is just a solder short some where on the board.
Look at the schematic and carefully check all the places the V3.3 goes. Reheat the pins on the header connectors (J3, J6) and through hole components in case there is a solder whisker you don't see. The distance from component pads to the ground plane is very small.
C26 is an electrolytic so it's possible it has shorted.
If you are very lucky the problem is just a solder short some where on the board.
Look at the schematic and carefully check all the places the V3.3 goes. Reheat the pins on the header connectors (J3, J6) and through hole components in case there is a solder whisker you don't see. The distance from component pads to the ground plane is very small.
C26 is an electrolytic so it's possible it has shorted.
Re: Working, but broke, 3.3V shorted.
@MnTech, yes, I have removed the display. I have no blinking LED's or anything so it's not booting even without screen.
My DMM says 5.6 Ohms over C26 on board. Sounds very little - will desolder and check in isolation. I mean, resistance over a any cap would be 0L (infinity since it's measuered with DC, right?). But it could be the surrounding circuit and not the cap itself? Replacing a 100uF cap would be the easiest fix I could think of so holding my thumbs! Thanks for the tip!
The board have been working for a couple of months so I'm not really going to bet on bad soldering, rather something burnt because of a temporary short somewhere (I have been using it uncased and snipped components on my messy desk so accidental but temporary short is low odds.
My DMM says 5.6 Ohms over C26 on board. Sounds very little - will desolder and check in isolation. I mean, resistance over a any cap would be 0L (infinity since it's measuered with DC, right?). But it could be the surrounding circuit and not the cap itself? Replacing a 100uF cap would be the easiest fix I could think of so holding my thumbs! Thanks for the tip!
The board have been working for a couple of months so I'm not really going to bet on bad soldering, rather something burnt because of a temporary short somewhere (I have been using it uncased and snipped components on my messy desk so accidental but temporary short is low odds.
Re: Working, but broke, 3.3V shorted.
Desoldered C26 and it was unfortunately fine:
