Startup test troubleshooting
Posted: Mon Apr 01, 2019 8:28 am
I have problems with three DSO shell units. Two of them did not boot up at all. One did boot up first time (with 9V power adapter), but next time I tried it did not boot up. One I tried with my lab power supply, and noticed that 1.5A went through the unit, until some component gave up a bit of smoke.
I have printed the schematic and did some testing yesterday.
Unit 1. Bought from Banggood. This did not boot when I first received it. This is the one that gave up some smoke after drawing 1.5A. When powering this on yesterday, using 3.3V (with the power supply, current limited) on the 3.3V point on the PCB, it draws about 700mA. The red diode lights up. The large IC (STM32 F103C8T6) gets burning hot within a few seconds. Too hot to touch. I only let this run for 5-10 seconds at a time. This PCB does _not_ have a short between 3.3V and GND. I suspect the IC has been destroyed.
Unit 2. I received this as a replacement directly from JYE Tech. This is the only one that booted up when I first got it (using the 9V power adapter). For some reason it didn't boot again. I noticed that there is a short between 3.3V and GND. I de-soldered the voltage regulator, as all legs seemed to be shorted. But after de-soldering this, there is no short between leg 1 and the others, though leg 2, 3 and 4 seem to be shorted (not sure if this is how it's supposed to be). After de-soldering the voltage regulator, I applied 3.3V to the 3.3V point on the PCB. I find no components that get hot. I turned up the current until 1.2A flows through the circuit. I still can't find any hot component. The large IC might get mildly warm, but not enough that I can be sure. I don't get burned by any components. Maybe there is a short through a small component somewhere, or on the trace? The red led does _not_ light up.
Unit 3 seems identical to unit 2. It did not boot up when I first got it, though. All legs of the voltage regulator are shorted (or 0.5 ohm).
How can I troubleshoot step 1? I saw that someone else just started a thread with a similar question. Unfortunately I don't own a IR camera, which I think would be usable for finding the short.
I'm thinking of desoldering some more components on unit 2 until I find the short. I hope I won't have to de-solder the large IC though.
I found this guide on the web, where 12V was used instead of 9V. The voltage regulator gave up smoke, as well as the STM32 IC. These were both replaced, and the unit started working again:
https://www.instructables.com/id/DIY-Os ... leshootin/
I have printed the schematic and did some testing yesterday.
Unit 1. Bought from Banggood. This did not boot when I first received it. This is the one that gave up some smoke after drawing 1.5A. When powering this on yesterday, using 3.3V (with the power supply, current limited) on the 3.3V point on the PCB, it draws about 700mA. The red diode lights up. The large IC (STM32 F103C8T6) gets burning hot within a few seconds. Too hot to touch. I only let this run for 5-10 seconds at a time. This PCB does _not_ have a short between 3.3V and GND. I suspect the IC has been destroyed.
Unit 2. I received this as a replacement directly from JYE Tech. This is the only one that booted up when I first got it (using the 9V power adapter). For some reason it didn't boot again. I noticed that there is a short between 3.3V and GND. I de-soldered the voltage regulator, as all legs seemed to be shorted. But after de-soldering this, there is no short between leg 1 and the others, though leg 2, 3 and 4 seem to be shorted (not sure if this is how it's supposed to be). After de-soldering the voltage regulator, I applied 3.3V to the 3.3V point on the PCB. I find no components that get hot. I turned up the current until 1.2A flows through the circuit. I still can't find any hot component. The large IC might get mildly warm, but not enough that I can be sure. I don't get burned by any components. Maybe there is a short through a small component somewhere, or on the trace? The red led does _not_ light up.
Unit 3 seems identical to unit 2. It did not boot up when I first got it, though. All legs of the voltage regulator are shorted (or 0.5 ohm).
How can I troubleshoot step 1? I saw that someone else just started a thread with a similar question. Unfortunately I don't own a IR camera, which I think would be usable for finding the short.
I'm thinking of desoldering some more components on unit 2 until I find the short. I hope I won't have to de-solder the large IC though.
I found this guide on the web, where 12V was used instead of 9V. The voltage regulator gave up smoke, as well as the STM32 IC. These were both replaced, and the unit started working again:
https://www.instructables.com/id/DIY-Os ... leshootin/