Brandnew product STM32 based product dead after a couple of hours. - Page 1
Forum section: electronics / general

author: peteb2
author_rank: Regular Contributor
timestamp: March 04, 2020, 10:13:31 pm
content: OK this is more a repair subject but i need to pick the brains of an STM32 guru please. From its unboxing, it took multiple power-on key presses to awaken the unit whereupon finally revealing plenty of charge via the icon in the onboard LCD. I powered it off & left it around 2hrs.When i next went to power it on i found any number of power-on presses nothing happened & recalled is sluggish startup previously. The two removable 18650 LiOn cells read fully charged on a DMM.Returning the unit under warranty will be an excessive cost so why not have a look deeper... right?So far my back-engineering on the thing reveals each press of the power-on switch puts 3.3V to a test point on the board as long as the button is depressed. Random multiple stabs can make NRST (pin14) of the LQFP100 STM32F103VET6 sometimes(!) go Hi and in that state all VDD pins for the STM receive 3.3V, so supply is latched on (it looks).Sadly nothing else is happening. Absolutely no action from any buss other than 3.3V on VDDA & other 5 pins for VDD. All VSS are showing continuity to the OV PCB plane.The ext Osc i/o pins 12/13 for an 8MHz xtal reveals utter deafness (using a teeny tiny mod'd scope probe tip viewing things using a pcb microscope so as not probe the wrong thing ). The xtal is silent probing all 4 solder lands with only a tiny voltage present. Nothing else on the internal 32KHz RTC, OSC32out & OSC32in either... (maybe the routine isn't using it anyway). It's like the chip is permanently asleep, bricked or DEAD.Over the years i have had similar brickages with other microcontroller based ccts i have been asked to bring back to life as a maint tech & found a dead xtal to be the cause but shouldn't the newer SMD one in the pic kind used be far more reliable?Do any of you STM32 gurus believe it **might** be the xtl or have i some how tripped the TAMPER port #pin7 & killed the thing fully anyway.... if the programmer bothered with including that too....The thing owes me a few bucks (its a bit of handheld test gear). If i can wake this thing up i'll learn something about hardware into the bargin.... Surely an STM32 is going to have somestuff happening on its pins no matter how asleep in shutdown mode it goes to save on energy... or am i wrong? Any ideas would be a great help even if it confirms this thing to be a lost cause.Thanks for any input...

author: thm_w
author_rank: Super Contributor
timestamp: March 04, 2020, 11:07:27 pm
content: If its a brand new product and failed out of box, consider asking the seller to pay for the return shipping and see what they say.If the 3.3V is present but the xtal is not doing anything, either the flash has somehow wiped itself or they have a check in the firmware prior to starting the XTAL up. I don't think it is that common to have that, but might depend on the end product.What is it?

author: peteb2
author_rank: Regular Contributor
timestamp: March 05, 2020, 04:52:15 am
content: I'm slightly concerned to name the brand of product here because it is a known Chinese brand and i don't want to 'bad name it' or 'wash my dirty laundry' on this website at this stage over the whole thing, for now. Interestingly i have today finally had a reply from the seller asking me to fully charge the cells, then make a video of the problem & email him.I've checked the lowest cost of shipping the item back to be well on the way to buying another new unit via Ebay!I'm pretty much screwed though as even if the thing does go back there's evidence of my having probed the PCB which i'm sure is pretty quickly an out on the warranty for the supplier.My recent experience with China produced technology was 'top-end' portable radio receiver that ceased working on AM. Even though Amazon whom i bought it from offered a warranty the return shipment to the States i was told i had to pay almost covered another receiver so i back engineered the thing (very little data available it) finding disgustingly bad leadfree soldering joins, tomb-stoned devices and finally a microscopic cap that went wrong after an hours use inside a pcb screened can for the AM stage PLL chip's xtal circuit. The poor XTAL would just stop oscillating....I guess i'll assume that the firmware for an STM32 takes if out of 32KHz self osc 'sleep' & and then uses the 8MHz reference. (Apologies i've never learned to program the STM32). That isn't happening which says the things a dead duck i guess. Beats me though, i would have thought that no matter how deep asleep-mode a devices is set to after power off that something on one of its hundred pins would show some sort of activity in some form of measurable pulseset/ heartbeat etc....

author: Psi
author_rank: Super Contributor
timestamp: March 05, 2020, 06:56:02 am
content: Check that the BOOT pins are not floating. I've seen odd behavior when they float.It doesn't take much noise and the MCU starts up in boot loader mode without you asking it to (at least on STM32F042)

author: mbless
author_rank: Regular Contributor
timestamp: March 05, 2020, 03:56:26 pm
content: Quote from: peteb2 on March 04, 2020, 10:13:31 pmWhat probe did you use? I believe you need a high impedance probe, otherwise there will be too much capacitive loading and the crystal won't start so it'll look like it's dead.

author: ogden
author_rank: Super Contributor
timestamp: March 05, 2020, 04:33:01 pm
content: Quote from: peteb2 on March 05, 2020, 04:52:15 amDid you look at solder joints of this device as well? If everything about joints are good - what about cleanliness? XO may have problems running on dirty PCB/pins. Did you check stm32 power rail voltage? If it is OK then try to reset MCU when power is stable by shorting reset pin to ground, then releasing it.Quote from: mbless on March 05, 2020, 03:56:26 pmUsually stm32 (8MHz) crystal oscillators are fine with 1:10 probe connected to OUT pin. Yes, you may get some clock glitch, but oscillator won't stop (in case it is started by boot code).

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 05, 2020, 04:41:41 pm
content: Would it be yet another product with a counterfeit STM32F103?

author: Psi
author_rank: Super Contributor
timestamp: March 05, 2020, 10:30:38 pm
content: Quote from: SiliconWizard on March 05, 2020, 04:41:41 pmSTM32F103 would definitely be the one they would counterfeit.

author: thm_w
author_rank: Super Contributor
timestamp: March 05, 2020, 10:47:30 pm
content: Quote from: peteb2 on March 05, 2020, 04:52:15 amParts can be faulty from any brand, what matters is how they respond to it.If you bought via ebay the onus is on the seller to resolve the issue:QuoteAs long as you didn't scratch the PCB, desolder parts, or make some obvious damage that would kill it, I don't see an issue with that. If you are sure its not caused by you, do not mention to them that you probed the PCB.

author: peteb2
author_rank: Regular Contributor
timestamp: March 07, 2020, 03:01:42 am
content: Boot pin tied to OV via a 10k. There’s also an unpopulated gold tinned pair of vias silkscreen labeled as a connector, one goes to Boot, the other the leg of couple of J3Y transistor/A3F reset devices that trace back to port pins 87 & 83 on the STM32.