"LC Technology" STM32F103C8T6

I have a generic board labeled “LC Technology” on the bottom and its USB doesn’t work. I decided to take a closer look at it on the scope. PA11 (USB D-) was at 5V and PA12 (USB D+) was at 3V, with just a steady voltage. Comparing to my other board, PA11 was at 0V and PA12 was at 3V and roughly every 1ms there’s some data. I assume that’s the USB Start of Frame (SOF). So I’m pretty sure D- shouldn’t be pinned to 5V.

Pictures:

LC-Tech-Top.jpg (140.01 KiB) Viewed 3277 times

Thanks for sharing this.

Take care with that board, the quality can be pretty low if it is the board I am thinking of.

Search this forum for “ugly board”. Also be aware that as shipped there is probably a zero ohm link between VCC and VBAT called R14.

This makes life very interesting if you add a button cell to power the RTC. The battery will explode. It is in other words a bad idea, unless you have a thing for exploding button cells. See here for details.

According to the STM documentation, this link should be omitted, or should be a small value capacitor (I can’t remember which document mentions the capacitor, or its value). I removed the link, and the RTC worked fine on mine. In short, (pun intended), remove R14, it is a waste of time, and potentially dangerous.

Also check the jumper settings, I seem to recall, that they are connected in some way with the USB pins, but I can’t remember exactly how, and I don’t have the board to hand. One of them may be your mysterious short to +5V

There is some other design fault on that board.

You may find it does not boot up when not attached to a PC.

I cant get the bootloader working on that board.

I have no idea why the bootloader does not work. I thought it may be something to do with the oscillator not starting up cleanly, but I tested a few changes, but I could not get it to work.

ahull wrote:Take care with that board, the quality can be pretty low if it is the board I am thinking of.

Search this forum for “ugly board”. Also be aware that as shipped there is probably a zero ohm link between VCC and VBAT called R14.

This makes life very interesting if you add a button cell to power the RTC. The battery will explode. It is in other words a bad idea, unless you have a thing for exploding button cells. See here for details.

According to the STM documentation, this link should be omitted, or should be a small value capacitor (I can’t remember which document mentions the capacitor, or its value). I removed the link, and the RTC worked fine on mine. In short, (pun intended), remove R14, it is a waste of time, and potentially dangerous.

Also check the jumper settings, I seem to recall, that they are connected in some way with the USB pins, but I can’t remember exactly how, and I don’t have the board to hand. One of them may be your mysterious short to +5V

@ddrown

OK

I’m glad it works for you. But not for everyone (not me )

RogerClark wrote:@ddrown

OK

I’m glad it works for you. But not for everyone (not me )

ahull wrote:<…>
suspect that the poor quality control and rough soldering may be the issue with the one you have.

I’m all for recycling of parts, so long as the QA is there.

The average lifespan of a consumer gadget seems to vary in inverse proportion to Moore’s law (perhaps we should call that Eroom’s law, or ahulls law).

The more transistors we cram in, the shorter the lifespan of the product, so anything that extends the service life of gizmos is probably a good thing…

However having said all that, why does that idiot on the left of that big pile of crap cheap components shortly to appear in the Shenzhen electronic market (and shortly thereafter, no doubt on ebay) appear to be eating a PCB?

saving face?

zmemw16 wrote:saving face?

Organoleptic QA test… may be taste?

TomaTLAB wrote:Organoleptic QA test… may be taste?

I had some time to mess with this board again today, and I used a soldering iron to pull the bridge between 5V and USB D- apart. And now the stm32duino bootloader works on it

Slightly blurry close up after picture:

IMG_20160305_114048-2.jpg (72.73 KiB) Viewed 1447 times

Some probing reveals that the shield on the USB connector does not appear to be connected to ground in any way as it is on the Genuino boards and most other USB devices. This is a potential ESD issue for me because I will typically touch off on the USB shield since it is usually the largest and easiest to access ground point. At least in my case, I’m going to solder it to the nearby ground connection to S1 to ease my mind. When it comes to ESD I don’t like to mess around.