Reverse engineering FNIRSI-5012H

[ataradov]

Hardware-wise the debugger is fine. I've never used ST-Link or its clones, so I have no idea what software works with it.

The comment applies to the debuggers that have voltage level shifters to accommodate multiple target voltage levels. In this case the debugger is fixed at 3.3 V.

The debugger will be powered from the USB, the target will be powered from the battery. Both sides are fixed at 3.3 V, so there are no issues with voltage levels.

[neuralsim]

OK, I've got everything now. Silly me, I only ordered 1 replacement chip :/ I can buy more but they take a long time to ship of course.

I'm kind of new to soldering. I bought an SMD rework station, but the air gun doesn't really work all that well. I happen to have some SMD breakout boards and a bunch of SMD cmos chips I ordered by accident (meant to get through-hole chips). So I figure I'll practice with that. To get the original chip off, I'm thinking I'll just use solder-wick instead of trying to use the air gun to heat it off the board. Then I'll do my best to mount the new one.

I'm really nervous about this, any tips to help me succeed, other than practice a bunch?

I'm really looking forward to flashing the new firmware on! Also, as I mentioned earlier, I'm a professional software engineer. I'll be happy to contribute any improvements I make to the firmware, assuming I succeed with the hardware mod! Alex, is there anything in particular you think needs work and you aren't actively working on now, or have put on the back-burner?

[ataradov]

I'm not sure how well solder wick will work on a TQFP part. I imagine it will not work too well. The better option may be to carefully cut the old device pins with exacto knife close to the package and remove the leftovers with the wick.

But the hot air is definitely the best method.

As far as improvements go, I'm not really interested in doing more work on this. It really needs analog front end improvement to be a real tool. And really it is still too cumbersome to operate except for a few simple cases.

[thinkfat]

OK, I've got everything now. Silly me, I only ordered 1 replacement chip :/ I can buy more but they take a long time to ship of course.

I'm kind of new to soldering. I bought an SMD rework station, but the air gun doesn't really work all that well. I happen to have some SMD breakout boards and a bunch of SMD cmos chips I ordered by accident (meant to get through-hole chips). So I figure I'll practice with that. To get the original chip off, I'm thinking I'll just use solder-wick instead of trying to use the air gun to heat it off the board. Then I'll do my best to mount the new one.

I'm really nervous about this, any tips to help me succeed, other than practice a bunch?

Use plenty of flux. Everything works better with more flux.

[neuralsim]

RE: no more updates - Sad but understandable. If I manage to get the firmware updated I'll poke around and see if there's anything I feel I can contribute. As an extreme novice in EE, I don't see much hope that I could build a better front-end for it or improve the existing one, but maybe someday that will be a project I decide to take on. But when it comes to software, I'm incredibly comfortable and confident with just about anything, including assembly language on a chip I've never used before, so maybe I'll have some bright ideas.

Anybody else have features or tweaks they'd like to see if I do manage to get it flashed? Also, what would a better front end look like/consist of?

RE: lots of flux - yeah, I knew that in an abstract way already from many sources over the years, but I'm definitely learning that flux really is the king of solder in my practice sessions.

I've decided to get either a real scope, or a USB scope/logic analyzer, so I'm a little less concerned about hurting the FNIRSI. Think I'll just go for it this weekend when I have time. I'll see if I can get the air gun to function. I probably shouldn't have cheaped out on my rework station. It only goes to 480 degrees, and maybe it is simply my (lack of) skill but the whole rig seems very inconsistent, sometimes the iron works great and other times it just heats the pins and doesn't melt the solder. The heat gun seems kinda hopelessly bad. But maybe I'm bad. Here's the one I got: https://www.amazon.com/gp/product/B07XC9VV2C/ref=ppx_yo_dt_b_asin_title_o08_s01?ie=UTF8&psc=1

[ataradov]

One of the bigger problems of this device is overclocking of everything. MCU is overclocked, ADC is overclocked (presumably, since we don't really know the ADC model).

There are a few decent frontend designs out there. The Rigol one can be used as a decent starting point.

But the bigger issue is that it is cumbersome to use. Knobs and a bigger screen are just better.

This device is still useful and I do use it from time to time if I need to quickly check if the signal is there or check UART baudrate. But if I need stuff like decode or accurate measurements, a real scope has no alternatives.

Generally those cheap air guns work fine. What is wrong about it? Does it not get hot?

[neuralsim]

Yeah the air gun doesn't seem to get all that hot, I've managed to use it to get some solder off boards I didn't care about messing up, combined with a desolder vacuum pump. I read through the entire thread yesterday and saw your recommendation to use a thin wire to pull underneath the pins, but it seems like the solder will just re-solidify before I get all 4 sides up. I'm just afraid I'll burn the board or something.

Oh well, I ordered a real scope that's coming this weekend, so I'm feeling more adventurous now with this one. You guys will probably laugh at it but it really looks good for the price. Hantek DSO5102P. I couldn't bring myself to spend another $150 for the $400 Rigol when I haven't even run into a need for a scope yet.

[ataradov]

Yeah the air gun doesn't seem to get all that hot, I've managed to use it to get some solder off boards I didn't care about messing up, combined with a desolder vacuum pump.

Why would you need a pump. Hot air should be able to melt the solder and then you just remove the component.

It is hard to tell if the gun is indeed under-performing or you are doing something wrong. Usually those heat guns either work or not at all. I assume you have tried to adjust air flow and temperature?

I read through the entire thread yesterday and saw your recommendation to use a thin wire to pull underneath the pins, but it seems like the solder will just re-solidify before I get all 4 sides up. I'm just afraid I'll burn the board or something.

The hot air gun must be able to produce enough heat to heat up the whole chip at once.  The wires are pulled when the solder has melted on all 4 sides.

[thinkfat]

Yeah the air gun doesn't seem to get all that hot, I've managed to use it to get some solder off boards I didn't care about messing up, combined with a desolder vacuum pump. I read through the entire thread yesterday and saw your recommendation to use a thin wire to pull underneath the pins, but it seems like the solder will just re-solidify before I get all 4 sides up. I'm just afraid I'll burn the board or something.

Oh well, I ordered a real scope that's coming this weekend, so I'm feeling more adventurous now with this one. You guys will probably laugh at it but it really looks good for the price. Hantek DSO5102P. I couldn't bring myself to spend another $150 for the $400 Rigol when I haven't even run into a need for a scope yet.

Well, "buy cheap, buy twice" is what they say. You bought cheap the second time already

[neuralsim]

Well, "buy cheap, buy twice" is what they say. You bought cheap the second time already

LOL it's a fair point... but this time I was a lot more careful to look at reviews and the specs of the device. Let's face it, there's no maximum price for a scope. There's always a more expensive one with more features and better bandwidth. I'm completely new to this game, I probably won't even need the scope any time soon, and I can't justify spending $400 - $20,000 on a tool I don't even need yet. I'm planning to do mostly arduino and simple hobby projects, I think the Hantek will last me quite some time.

Really I could probably get by with the unmodified FNIRSI, it did fine testing my signal generator. But I figure it will be nice to be able to look at non-periodic signals someday.

The first real workout the Hantek will get will probably be when I build my bench power supply. Someday when I learn what the heck I'm doing, I figure I will build my own oscilloscope. That day is a long way off.

[neuralsim]

The hot air gun must be able to produce enough heat to heat up the whole chip at once.  The wires are pulled when the solder has melted on all 4 sides.

Ahh. But the chip is surrounded by tiny little smd parts... capacitors I guess? How to avoid dragging those along for the ride?

[ataradov]

if you heat the IC itself (from the top, but concentrating towards the sides), then surrounding components will not heat enough. Or even if they do, they will be held by the solder tension.

You need to adjust air flow so it does not just blow everything away. Generally the lowest flow possible works fine for that.

[neuralsim]

You need to adjust air flow so it does not just blow everything away. Generally the lowest flow possible works fine for that.

That's probably my issue. I just turned the knob all the way to the right. Less flow equals more heat. That makes sense. Thanks for being so patient with my beginner @55.

[thinkfat]

You need to adjust air flow so it does not just blow everything away. Generally the lowest flow possible works fine for that.

That's probably my issue. I just turned the knob all the way to the right. Less flow equals more heat. That makes sense. Thanks for being so patient with my beginner @55.

That depends on how cheap the hot-air gun is. If it's properly regulated (even if it's just half-arsed), more airflow means more energy transfer.

[neuralsim]

That depends on how cheap the hot-air gun is. If it's properly regulated (even if it's just half-arsed), more airflow means more energy transfer.

It's about as cheap as they go, so my guess is there's nothing proper about it. Unfortunately I don't have a thermocouple that can measure temperatures this high so I dunno how hot it actually is. I'm just gonna play with it for a bit and then go for it on Saturday. Wish me luck!

[CChin254]

The hot air gun must be able to produce enough heat to heat up the whole chip at once.  The wires are pulled when the solder has melted on all 4 sides.

Ahh. But the chip is surrounded by tiny little smd parts... capacitors I guess? How to avoid dragging those along for the ride?

Kapton tape may help.

[neuralsim]

Aborted the mission this weekend, I got a 3d printer and spent most of my weekend trying to get the damn thing set up. May try it tonight.

I did get the Hantek though, and it's a very nice little machine for $250!

[neuralsim]

Finally got the chip off and the new one on, but a few of the pins are connected according to my multimeter . I assume none of the pins are supposed to be connected?

I can't see a bridge in my microscope, either. Bummer

[ataradov]

What specific pins you are talking about? Have you seen the pictures of the board with the chip removed (first page of this tread)? You can clearly see what pins are supposed to be connected.

There are not a lot of of pins connected, but there are multiple pins that are power supply and grounds, and they all are connected together.

[neuralsim]

What specific pins you are talking about? Have you seen the pictures of the board with the chip removed (first page of this tread)? You can clearly see what pins are supposed to be connected.

There are not a lot of of pins connected, but there are multiple pins that are power supply and grounds, and they all are connected together.

Just checked, it's those pins! So maybe I was successful after all.

[neuralsim]

Well I did a connectivity test on each pair of pins and checked for continuity and bridges, I got 100% with my multimeter. So now I need to solder a micro connector. I took pictures of my SWD board can you help me figure out which pins I need to connect? Edit: never mind, I've got it I think. Missed the diagram in the middle on the back side of the board, I see the pins from the docs.

So now solder a connector, plug the programmer into my PC along with the multimeter, install OpenOCD or whatever it's called, power on with F2 and flash the code, right? I'll try that out tomorrow, it's super late here.

[ataradov]

You don't need F2 on a blank device, but generally yes, this is the process. I don't know anything about those programmers, so it would be on you to figure that out.

[neuralsim]

You don't need F2 on a blank device, but generally yes, this is the process. I don't know anything about those programmers, so it would be on you to figure that out.

Yeah, fair enough. If it recognizes the board but can't flash it for some reason I'll probably just buy yours, I should have done that anyway to thank you for your work on the project. I'll hit your tip jar if I get mine to work.

[neuralsim]

I've got openOCD installed and I'm trying to use it, not having a lot of luck because I have no idea what I'm doing. I need to compile the code to some format and run a flash utility on it, right? GCC I guess? I'll figure it out eventually I guess!

[ataradov]

You can use binaries attached to this thread. You don't actually need to use GCC or compile anything.

But you need to get OpenOCD to recognize your debugger and your chip. And I really have no idea about that.