Garage door module Nice SNA4/A - burnt component

[CapLeaker]

Umm… if you shorted that TVS and the thing works, then there can't be a bidirectional voltage protection device in there. This “device” is going from the positive from one cap to positive to the other cap? I think we should have pics from top and bottom on the first go around. It just doesn't make any sense to me to have one supply, go into a cap, then use a fuse and go into another cap. For what? What does the second cap power? Maybe post some straight shot pics from top and bottom, to see what's going on here.

[jm1234]

I had an older picture without the caps, should be easier to trace.

[jm1234]

The bottom picture shows bi-di TDS soldered. One pad is missing, but it is indeed soldered on the other side of the board.

[redwire]

It's not an easy PCB to trace out.
Polarity is not making sense if (- from the rectifier) goes to that connector outside pin. Is it reversed with "+50VDC from rectifier pin"? Are you sure that's right?
Which is (+) and (-) on the 63V 2,200uF cap by the 100k resistor? And the 63V 1,000uF.

So far it looks like a blocking diode, one end (cathode?) facing connector trace goes up to the relays. That would mean it's a battery isolator diode.
Where does the battery connect? I guess the 2-pin grey connector bottom right.

[jm1234]

I forgot to mention, all the caps have their negative oriented towards the 5-pin connector and their positives towards the gray plastic connectors.
That 5-pin connector is probably for battery, but i'm not using battery, so I'm not sure.
I'm pretty sure about the 0/- being the outside pin on the large connector, because all the caps negative poles are connected to it.
As to how difficult this is to read, I'm barely making things out and I'm holding the board. I have no idea how you guys can make sense of this using pictures.

[jm1234]

The grey plastic connectors are NOT for battery, I'm pretty sure about that.They are for start/stop and other commands. Like I wrote above, I think battery is meant to be connected to the 5-pin connector.

[redwire]

OK that connector has high current thick PCB traces, but it seems to be for a lightbulb. Battery option is some small 1.2Ah with built-in charger.

Just need the polarity of the caps to figure this out.

[jm1234]

Light bulb is connected to 2 of the 4 separated pins where that longer relay is. I commented on the polarity of the caps above.

all the caps have their negative oriented towards the 5-pin connector and their positives towards the gray plastic connectors.

[redwire]

What you call "- from rectifier" connector pin the PCB trace goes to the capacitor pins away from the 5-pin connector (+)?. So I think that is not right.

Anyhow... the mystery part is in series with DC power to the relays (motor). That makes it an ordinary diode. The purpose might be to prevent backfeed/regeneration into the DC power if the door/gate moves on its own. A DC motor can act like a generator if you spin it, and a moving door or gate can do that. Sorry I was wrong about a GDT or TVS, whatever I said earlier.

Original might then be a cooked MR756 diode. A replacement (plastic) diode would be 6A02 thru 6A10 (for 6A) or a big fat 10A02 thru 10A10 (for 10A) same size leads. Cathode band towards the relays. I think a 6A part at 200-600V is strong enough.

[jm1234]

I'm so grateful to both you guys redwire and CapLeaker, thanks a lot!

[CapLeaker]

We should have had the second pictures you took first place around. I agree with redwire, that device is just a blocker diode. It's starting making sense now being able to see the full top and bottom. Pictures are important, as you can see…

[jm1234]

Well, spoke to soon. Sometimes the board comes alive (even with 31V bench power supply), but most often it won't. I cannot find out why. I tried to heat the board up from down below, but it didn't make any difference.
The power supply shows few mA for a moment, but then it goes into 0mA, so nothing seems shorted. The 1st 2 caps (around that burnt diode) get charged, but nothing else does.
I cannot work out how the rest of the board should get powered. Neither of the 2 DC-DC chips have any power either.

[CapLeaker]

Cold solder joint or bad through hole maybe?

[redwire]

The new diode might be in backwards if I gave more bad advice? Cathode is away from the relays eek if "- from rectifier" is right in your drawings. If the pad has lifted off, you can use other pad, put it there like pic.


The fuse is good and has power? Check the TO-220 below it and the big resistors. Can you read any numbers on the TO-220 parts?
This supposed to be a 24VDC board but has 50V coming in? Must be a buck converter from 50V to 24V, the heatsink by the 24V relay below?
There are two buck-converters that have the blue inductors "101". If there is no power there, then look upstream.
I think it goes 50V raw in -> 24V ->12V -> 5V. This board is a bit crazy.

[jm1234]

Found the issue, it was right between the chair and the desk. Mistake on mistake, but I did figure it out. I was tracing why those other caps don't have any voltage and it turns out there is another lower-voltage supply on the 3rd pin on that big connector. I was going off of my memory since I got back to looking into this, so that's what I didn't remember. The cases when I was able to make the board come alive must have been when I accidentally connected my power supply to that 3rd pin I guess.
What i don't understand is that voltage supply on 3rd pin comes directly from transformer (so bypasses rectifier) and when I measure it it shows 25VAC, but when I switched my multimeter to DC, it shows 7.5VDC.

[redwire]

There is that other rectifier diode on the board, it must 1/2 -wave rectify the 25VAC and there is that big blue resistor to drop it down.