Bernina control board

[snoptel]

Hi everyone.

I have a strange one here.

The PCB in the picture is from a Bernina Artista 200 embroidery machine that was given to me.

Plugged it in and nothing happened. Opened it up and found remains of water and a blown capacitor, (Circled in the picture).
Replaced the cap and the screen back light came on and the screen as well, but nothing happened afterwards. Turned it off and then back on and it´s back to being dead.

All four voltages are present, indicated by the four LED´s on the top of the board.

The IC that's circled get extremely hot, which leads me to believe there´s a short somewhere.

I´ve cleaned the board with alcohol as there were some areas that had water stains. I don´t see any shorts on the IC pins anywhere.

On of the caps looks slightly bulged compared to the others, I may end up replacing it.

Of course, no schematics online.

Any help/ideas are greatly appreciated.

[stj]

Re: Bernina control board

thats just i/o
where's the computer? is it plugged into those strip connectors?

[CapLeaker]

Re: Bernina control board

What are the 4 voltages? The LC14A is a Hex Schmitt Trigger inverter. If you look up the datasheet, it should be on a 3.3V rail. Check pin 14 for voltage. I know what these embroidery machines cost, those aren't cheap. I'd replace that hot IC and see what happens. For shits and giggles, remove that hot LC14A IC (either with a hot air station, or carefully cut the legs, take the casting out, then remove the leftover legs with solder and solder paste. Clean it and turn it on without that IC. See what happens...

I wonder if the bad IC sucking the 3.3 rail down for other chips to work.

[snoptel]

Re: Bernina control board

thats just i/o
where's the computer? is it plugged into those strip connectors?

Yes Sir..
The pc is on the back side of this board where you see those two strips.
I removed it when I cleaned the board.

[snoptel]

Re: Bernina control board

What are the 4 voltages? The LC14A is a Hex Schmitt Trigger inverter. If you look up the datasheet, it should be on a 3.3V rail. Check pin 14 for voltage. I know what these embroidery machines cost, those aren't cheap. I'd replace that hot IC and see what happens. For shits and giggles, remove that hot LC14A IC (either with a hot air station, or carefully cut the legs, take the casting out, then remove the leftover legs with solder and solder paste. Clean it and turn it on without that IC. See what happens...

I wonder if the bad IC sucking the 3.3 rail down for other chips to work.

The voltages are 3.3v, 5v, 12v and 33v.

When powered up, the LEDs light up indicating the voltages are present.

I will check the voltage on pin 4 later today. As for removing the IC, if I have a spare moment tomorrow I'll tackle it
Thanks for the help.

[momaka]

Re: Bernina control board

The voltages are 3.3v, 5v, 12v and 33v.

When powered up, the LEDs light up indicating the voltages are present.

Don't trust the LEDs - they could be just tied to each of those rails with a resistor and could be lighting up even when the rails are too low. Take a multimeter instead and measure the voltage on each rail to confirm it is what it should be (give or take 5%, usually... and maybe 10% for the 33V rail.)

For shits and giggles, remove that hot LC14A IC (either with a hot air station, or carefully cut the legs, take the casting out, then remove the leftover legs with solder and solder paste. Clean it and turn it on without that IC. See what happens...

Concur.
Though a safer way to remove the IC without possibility of damaging the board by cutting the legs (at least to me, this seems a bit dangerous, but perhaps it depends on the person doing the task too) is to "flood" all of the pins on both sides with leaded solder and repeatedly heat up each side while applying very gentle lifting pressure on the IC. Once the IC gets a little off the board, you can continue the heat & lift method in bigger steps until the IC is off.
... or if you have TWO soldering irons, apply leaded solder on all of the pins on both sides of the IC and heat up the IC on both sides with the two irons simultaneously, then slide the IC off the board when the solder melts. I usually use this 2nd method. In fact, I'm often able to do it with a single iron, provided the IC is small enough that I can take a really big blob of solder and melt it over both sides of the IC simultaneously (hint: a big, fat, spoon or chisel or bevel -shaped tip on your iron is recommended for this.)

[snoptel]

Re: Bernina control board

Hi guys, I apologize for the tardy reply, but I´ve been super busy plus my hot air station isn´t working - Murphy's law.

I checked the voltages, I´m getting what's expected, 5.05vdc, 37vdc and 12,5vdc.

I can isolate the 12vdc rail from the 5/33vdc rail via a two plugs. The aforementioned IC heats up when the 5/33vdc rail is on.

I hope to use a friends hot air station tomorrow, hopefully removing the IC clears the short..

One more questions, I did some probing around checking the capacitors, and there are a lot that are grounded on both sides. I know that checking components in place isn´t always the best way to go, but has anyone ever come across this before?

Thanks.

[momaka]

Re: Bernina control board

One more questions, I did some probing around checking the capacitors, and there are a lot that are grounded on both sides. I know that checking components in place isn´t always the best way to go, but has anyone ever come across this before?

Yes.
If the capacitors in question are all in parallel, it really only takes one to be shorted for the whole lot to appear like they are shorted. Generally, this happens with ceramic capacitors more than any other kind, and typically when there are multiple of them filtering a power rail. However, it could also be a faulty IC (the one that overheats?) that has a short to ground, especially if that short-circuit is on its input power rail - in such case, any capacitors attached to that power rail will appear as shorted but may not be.

That said, try measuring the resistance to ground on both side of the caps rather than using continuity (beep) function. Do both sides of the capacitors that appear shorted show the same exact very low resistance? (i.e. same as when multimeter probes are shorted together.) One side should clearly show a short-circuit to ground, as that would be an actual ground. The other may or may not. If not, then that's likely a power rail.

In any case, looks like you may just have to remove the IC either way.
Again, if you don't have hot air but do have (or can get) two soldering irons, that will work fine too. Any cheap 25-35W iron will probably do the job as the second iron. So that gives you an option if you can't get ahold of a hot air station.

[snoptel]

Re: Bernina control board

Update..no joy.

I removed hot IC, no change. (Plus I think I lifted a track :S)
As I wrote in the initial post, the cap circled in blue looked somewhat bulged, so I removed it..no change.
kind of bummed out. Any suggestions?

The other ceramic caps are still grounded on both sides. The short is somewhere else.

[CapLeaker]

Re: Bernina control board

Either you need something like a LeakSeeker 89 or inject power with a lab grade CC CV power supply and see what is getting hot now.

[snoptel]

Re: Bernina control board

Either you need something like a LeakSeeker 89 or inject power with a lab grade CC CV power supply and see what is getting hot now.

Hmm, a LeakSeek would be nice..they´re hard to find now a days.

Have to see If I can get a hold of a lab PS.

[snoptel]

Re: Bernina control board

I´ve traced the 5v rail to in red. Goes to a component that I can´t seem to make out the number - 3Bs something. Not sure if it´s a voltage regulator or something.

I was thinking of removing the cap at the beginning of the 5v rail and checking the other if shorted, and going from there working my way forward..

Also, I noticed that the regulator circled in blue was quite hot, removed it but that just cut the 33vdc and didn´t solve anything. (This was just for some piece of mind.)

I left the board powered on for 5 mins and felt around.. the IC circled in yellow get quite warm, the others don´t.. model is: AHC16244

[CapLeaker]

Re: Bernina control board

I could have been that transistor, since the voltage IS present. You are looking for missing voltages to identify where your problem is. The injecting power trick only works if something is shorted to ground.

[snoptel]

Re: Bernina control board

I could have been that transistor, since the voltage IS present. You are looking for missing voltages to identify where your problem is. The injecting power trick only works if something is shorted to ground.

I´m assuming your talking about the transistor at the end of the red 5v rail??

I may have one on some salvage PCB´s.
I´ll take a look and if so, swap it and hope the stars align.

[momaka]

Re: Bernina control board

Even if the transistor is bad (or not), I still think the caps that show short-circuit on both sides are the ones to worry more about.
I don't have a LeakSeeker either, nor a good enough lab power supply... so my usual plan of attack for such boards is to keep removing components until I get to the shorted one. In the case of the shorted caps, if they are ceramic or tantalum, start removing them one by one and test each out of the board. If good, and the resistance across the other ones still shows shorted, keep removing them one by one. You can also solder them back in once each one is checked and showing OK. May seem like more work, but at least for me, removing and putting back those small caps is usually easier than removing whole ICs or looking for replacement transistors.

[CapLeaker]

Re: Bernina control board

My last post should have read “couldn’t be the transistor”. I guess my iPads spell checker messed around. If you don’t have any of these devices, you have to do what momaka said. You also can break things in sections by cutting the shorted trace in specific sections. Then measure which section is still shorted to ground. That should could down the area you need to look at.

[kaboom]

Re: Bernina control board

Re the CC/CV power supply to heat up "shorted" components:

If they're well & truly shorted, they'll drop little voltage, even with a few amps through them. So you won't always find them this way.
Had a shorted SM MLCC a few months ago in something unrelated.
There were multiple in parallel- had to pull & measure each to find the shorted one.
Backfeeding with a current-limited PS did NOT help here.