Jump to content
Boogieman

Gotway Tesla, MosFet legs covered in laquer, should i leave it be?

Recommended Posts

Posted (edited)

Ok, so i did my first full teardown on my tesla v1.2 as i was changing tyre (was curious and want to move beeper....add tail light...paint some stuff....add some better dampening of the main board that rattles in the slots...cant be goodnfor gyro).

I found one of the mosfets LEGS were "glued together" by circuit board laquer.

I dont know if this is good (aka can prevent shorts between legs)

Or

If this is bad (aka laquer leads electricity which can overload the electronics)

Any electric guru here that could say if i should

A. Leave it be(my favourite, if it works dont mess with it)

B. Remove laquer with i.e. a tooth pick (to decrease risk of burnt mosfet) . Im thinking it could pick up dirt, that could get moist, that would lead electricity (for example I found a dead fly on the main board :-) )

 

See attached image

20200519_181326_copy_720x1280.jpg

Edited by Boogieman

Share this post


Link to post
Share on other sites

Additional question.

Anyone here that knows what the free slots on the circuit board is?

Inwant to connect a red tail light. Thinking in parallele with front light (risk of overloading led driver?) But even better if one of the outlets are allready constant led power :-)

see image

20200519_182354_copy_1105x633.jpg

Share this post


Link to post
Share on other sites
Posted (edited)
4 hours ago, Boogieman said:

B. Remove laquer with i.e. a tooth pick (to decrease risk of burnt mosfet)

Most probably (99%) not. It theoretically could be some remaining solder flux residue which could increase s bit corrosion (about negligable).

EUC mainbaords are normally coated with some "humidity secure thing" which should never be removed. As the wheels are not really watertight.

Edit: the photos don't have enough resolution to see anything in detail once one zooms in to pin level.

Edited by Chriull

Share this post


Link to post
Share on other sites
13 hours ago, Chriull said:

Most probably (99%) not. It theoretically could be some remaining solder flux residue which could increase s bit corrosion (about negligable).

EUC mainbaords are normally coated with some "humidity secure thing" which should never be removed. As the wheels are not really watertight.

Edit: the photos don't have enough resolution to see anything in detail once one zooms in to pin level.

Oh, i could se the laquer if i zoom first photo. But here is a non resized zoomed screenshot (max limit 3Mb prevents full sized images)

Screenshot_20200520-121211_Gallery.jpg

Share this post


Link to post
Share on other sites
29 minutes ago, Boogieman said:

Oh, i could se the laquer if i zoom first photo. But here is a non resized zoomed screenshot (max limit 3Mb prevents full sized images)

 

My first impression is that the solder was molten up again and distributed on the PCB?

I'll take another look later on the computer monitor - maybe i can recognize this better...

Share this post


Link to post
Share on other sites
1 hour ago, Boogieman said:

(max limit 3Mb prevents full sized images)

I assume the wheel is still working without problems?

It almost looks like the two legs are connected and should (imho, afaik) be not. But the image is a bit unsharp and with some laquer on it hard to see it in detail...

Best you show it to someone experienced with electronics in real life?

Share this post


Link to post
Share on other sites

Its definately laquer, with air bubbles in it as I believe the boards are sprayed rather than dipped. Its fine, dont touch it.

Share this post


Link to post
Share on other sites
9 minutes ago, Planemo said:

... I believe the boards are sprayed rather than dipped...

I've always assumed it's a brush-on laquer (or silicone-based conformal coating) based on the brush marks I can see in the material on all of my boards...

Share this post


Link to post
Share on other sites

However its applied, its often viscous enough to trap air bubbles on application. In any event, given its there for protection I wouldnt go anywhere near it, let alone poke around with delicate components in abundance.

Share this post


Link to post
Share on other sites
12 minutes ago, Planemo said:

... In any event, given its there for protection I wouldnt go anywhere near it, let alone poke around with delicate components in abundance.

I agree wholeheartedly!

 

Share this post


Link to post
Share on other sites
17 minutes ago, Planemo said:

However its applied, its often viscous enough to trap air bubbles on application. In any event, given its there for protection I wouldnt go anywhere near it, let alone poke around with delicate components in abundance.

I still cannot really identify this "silvery spot" between the two legs. Could be just from the reflections/deflections/refractions of the laquer, but also the mosfet/the pcb traces getting hot enough to melt the solder, let it distribute and create bubbles in the laquer?

Share this post


Link to post
Share on other sites
Posted (edited)
On 5/20/2020 at 9:29 AM, Chriull said:

I still cannot really identify this "silvery spot" between the two legs. Could be just from the reflections/deflections/refractions of the laquer, but also the mosfet/the pcb traces getting hot enough to melt the solder, let it distribute and create bubbles in the laquer?

Did you notice the inconsistency of solder connections between the legs on all ICs? At the bottom of the first picture I see "almost nothing" next to "gob of blob." Are some joints looking cold?

On the recent zoom-in picture, the IC in question,

  1. the first solder joint (toward the bottom) looks like the board eroded from too much heat, and/or the top of the PCB and the hole for the pin is visible (or it could be flux deposits). It does not appear like a good, reliable joint.
  2. the second joint looks cold with solder BBs (bad flux causing spatter instead of flowing? moisture? impurities (dirt) in the conformal coating?).
  3. the third joint (top of the picture) looks brittle, and that it might short with the 2nd joint.

It's hard to tell conclusively from the pictures, and understandably hard to take the pictures too. Those do not appear to be quality welds.

If I had to guess, from pictures alone, I'd say the ICs look like they were hand soldered given the flux on the board (the flux is generally acidic and should be cleaned off). (Over time, the more I think about the board in general the more I see wrong. Gotway Quality Control is, um, well...do they have Quality Control? It looks like they put a moderate effort into design and significantly less into production.)

13 Common PCB Soldering Problems to Avoid

 

Edited by WI_Hedgehog

Share this post


Link to post
Share on other sites

As long as it is clear laquer and not silvery coloured solder between the legs of the mosfet, it is fine to leave it alone. It’s a protection from moisture. 

Share this post


Link to post
Share on other sites

Thanks for all the replies.

I have tried looking with my eyes from every single angle and taking photos with and without flash, but i can not see"past the laquer bubbles" add they reflect what i see covering the solder joint.

One leg looks like a cold joint in the image, but that's just burnt flux (all other legs look well soldered on top and the ones i can see looking under the board on the tiny gap also below.

Reason i got worried was that my last "crash" was a low speed crash into a low steel pole (was taking of and came to a sudden stop and when looking down i saw wheel fighting to accelerate causing the horrible overload sound (hum) so i immediately stepped off (with cracks in my big toe its later turned out). I was really scared i had burned a MFET but i could roll away without problems. 

Since it's the center FET its also the one most likely to overheat getting heat from the other fets, but i guess since the wheel is spinning all of them are ok, or could the wheel function with one of them broken?

I have not made any high speed runs after this due to my toe

Share this post


Link to post
Share on other sites

Looking at this again after thinking about it, and taking some time to view it on a bigger screen, starting with the Surface Mount Device mounting:

  • Flux screening seems iffy. This is really hard to do well, and they don't seem to do it well.
  • Parts placement sucks. It looks like it was done by hand, although it is probably automated and the pick & place machine's bearings are worn.
  • The reflow soldering isn't great (not enough solder paste).
  • The board washer looks like it is working okay. (Clean board! Yea!)
  • The ICs are hand-soldered after the board is washed, and the flux is not being removed (poor work).
  • The conformal coating is most likely being applied by brush instead of a conformal coating machine, and a brush that needs to be replaced at that. There's a lot of dirt and bubbles trapped in the coating, so chances are nobody washes their hands (ever), and the environment is "less than clean." (Is that some Kung Pao trapped in there? On the left, next to the rat droppings....)

Typical Chinese work, which is all about manufacturing volume.

There are some great companies in China that do incredibly good work for very reasonable prices. This is not one of them.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...