Garage door module Nice SNA4/A - burnt component

[jm1234]

Hi,
I'm trying to guess what component got burnt on the control board for my Nice garage door motor Nice SNA4/A. You can see it in front of the 2 capacitors. The component is connected across the 36V rectified input wires, maybe it was some kind of protection device?
All the pictures I could find were of the whole product, so enclosed in the plastic box, eg. https://www.ebay.co.uk/itm/123998876212
Any help appreciated.

[jm1234]

Better focused picture

[jm1234]

actually it's rectified 35V AC, so it's 50V DC

[stj]

i think it was a GDT
small one made of glass - the bigger ones are ceramic to prevent that!

[stj]

if it's 50vac input then you need one rated atleast 75v - maybe 100v

[jm1234]

Thanks for the suggestion, just learned something new again :-).
However, thinking about it some more, my bridge rectifier was not damaged, it still produces those 50V. Not sure how would high voltage appear on that GDT to burn it then?
Also, does it seem the right place for GDT to put it after the bridge rectifier?

[stj]

not sure about the design, i wouldnt use a GDT,
a GDT will latch on once it trips until the voltage drops a lot - a MOV is safer but slightly slower

[redwire]

I agree the busted part is a GDT but not sure why it exploded. Did it just pop, they are gas-filled under pressure. No signs of heat. I thought the fuse would blow before it heated up enough to explode.
It's seems to be a worm gear reduction, so you could not push against the door and generate high bus voltage.
*Is that big Jamicon preggo, rusty at the top?

The lowest voltage available GDT's are rated 75V ±20%. Most common are 90V. Once they are ionized lit up, they stay on conducting like 12V arc at 1A. Until zero-cross if AC is present. This one seems to go on the DC bus- which is not the brightest idea. MOV are what you use. It typically is a 24VAC mains transformer making around 35-40VDC but the motor seems to get higher voltage. I think a toroid power transformer is inside and a bridge rectifier board as well.
Could not find board pics or decent info on the Nice SNA4.

Garage door openers are susceptible to lightning. Overvoltage transients come in on mains, or on ground between the door rails/frame and PE ground.
The Nice has no PE ground connection? So much plastic.
More on garage door opener lightning protection in this thread: https://www.badcaps.net/forum/troubl...e4#post1815406

[jm1234]

Both caps are bulged, need to replace them. I think the only other thing that popped was fuse on 220v side.

[stj]

jamicon are always shit

[CapLeaker]

Replace the GDT with a bi directional TVS and call it a day. The GDT may have a higher surge capacity, but here I can't see it being an advantage over a TVS. If you want you can theoretically triple your input protection by GDT, TVS, MOV all in parallel. Lol

The TVS or MOV would be my choice, because I don't have any GDT's in stock. As long as the rating is correct on the surge protection device, you can't do anything wrong here. If you take the damaged GTD out, the board should work again, less the protection of course.

[redwire]

I think you'd have to sketch the circuit around the GDT and see what is going on, there should not be 75-90V there, and current long enough to heat it up and blow it up. The fuse should pop quickly before all that.
Then there are the bad electrolytic capacitors. Strange failure. I keep thinking the motor regen with low value caps did it, but again it's a worm gear so the motor should not backspin.

I haven't seen Jamicons since the 1980's lol in CRT monitors, arcade games.

[R_J]

Littlefuse makes a mov that looks similar IE V47MT2B or Harris V68MA3A

[CapLeaker]

Littlefuse makes a mov that looks similar IE V47MT2B or Harris V68MA3A

Looks a bit small to me… and the leads are thin too.

[R_J]

Looks a bit small to me… and the leads are thin too.

"similar" as in not exactly the same.

[redwire]

I've never seen a GDT with such thick leads as OP's. That makes me thing it's a TVS or diode, MR756 first thing to come to my mind. Or maybe some other 6-10A diode? What does a 6A10 look like inside. No PCB silkscreen hard to know if the part has polarity.

The reason for a big diode I think is the 24V gel-cell power option for this opener, it might be protection against reverse-polarity? Was a battery wrongly connected letting smoke out?

[CapLeaker]

I've never seen a GDT with such thick leads as OP's. That makes me thing it's a TVS or diode, MR756 first thing to come to my mind. Or maybe some other 6-10A diode? What does a 6A10 look like inside. No PCB silkscreen hard to know if the part has polarity.

The reason for a big diode I think is the 24V gel-cell power option for this opener, it might be protection against reverse-polarity? Was a battery wrongly connected letting smoke out?

That's exactly what I would put in there… a TVS and call it a day.

[jm1234]

Just got back to this, sorry about the delay. I bought TVS https://www.tme.eu/ie/en/details/1.5...dil/1-5ke68ca/.
When I put it in the PCB, I noticed tha TVS is connecting + poles of the 2 biggest capacitors. So I can see the supply voltage on the 1st capacitor, but it doesn't get to the 2nd capacitor. That's a homework I should've done before bying TVS, sorry about that.
If I understand this correctly, TVS isn't the right way to address this, as I need that voltage to be passed onto the 2nd capacitor (and the rest of the board). Instead of the over-voltage protection that TVS provides, I probably need some over-current protection there, right?
Thanks in advance.

[CapLeaker]

Huh? So you bought a 68V TVS that protects a 50V capacitor? A TVS you can buy in unidirecttional and bidirectional versions. So it matters which way you put the unidirectional TVS in. You gotta read up on how these protection devices work. The protection devices work on over voltage, like TVS, MOV etc. vs over current like a fuse. That what is in there is not a fuse. In it does guaranteed not feed one big cap to the next via a TVS or whatever. Would be idiotic.

This is connected between the positive poles on the 2 capacitors? It should work as intended. Matter effect, the whole thing should work without the TVS installed. You got another power supply missing that feeds the other cap.

Maybe re upload some more pics and from the bottom too.

[jm1234]

Replace the GDT with a bi directional TVS and call it a day.

Not saying I don't need to learn, that is absolutely true. I just took the lazy path of following your advise literally, without thinking further. I see the PCB, not you, so I should have traced more before asking.
Anyhow, I shorted the TVS and it started to work. Coming back to my original question, what should I put instead of that burnt component. Knowing now, that this component connects + poles of the 2 big caps, I think GDT doesn't make sense, as it doesn't conduct under normal circumstances.
As for uni-directional TVS, it would pass the current in one direction, so the device would work. However, I don't understand the protection function here - it would only protect against reverse polarity until the break-down voltage and then it would just start conducting in reverse.
Pls correct me if I'm wrong here.
Appreciate all your help.