Short to gnd display board Honeywell Relay Module

[WHaThEFLuX]

Hello All,

Back at it again with another board issue.......


I unknowingly plugged a display module that had a shorted diode into this board, the result was a puff of smoke and the crater by the ground plane seen in the picture below. Having another board with the same issue, I began to test and remove components one by one with the hopes of figuring out what the shorted diode destroyed but haven't had any luck.

It seems that many components are shorted to ground as well after the initial incident, I'm not sure how else to diagnose this issue other than removing every single component until the short disappears.

As always any ideas or advice would be greatly appreciated!

[budm]

Re: Short to ground on display board, how to find the culprit?

So you have a board with shorted circuit that you connected to this board and it blew up the inductor L??.
Are you trying to find out where the shorts are in the display board or you are trying to find out what get damaged on this board when shorted board is connected to this board?

[stj]

Re: Short to ground on display board, how to find the culprit?

multi-layer.
if you want any chance of fixing that, you need a schematic - there is probably damage between the layers.

[WHaThEFLuX]

Re: Short to ground on display board, how to find the culprit?

Thanks for the quick responses guys!

Bud, I found the shorted diode on the display board, replaced it, and now it's working correctly. I'm trying to determine what is shorting to ground on the board in the picture, and it seems to be everything, literally.

I'm afraid stj is probably right, and there is most certainly no way of obtaining a schematic for this board. Anything I can try to salvage this thing or is it not worth the effort? As an interesting side note, I've repaired the same model board with the same burn mark, just not as severe, should I assume that on those boards the damage wasn't bad enough to affect the layer under it?

I'm still trying to wrap my head around single layer boards but multi-layer? That a whole new dimension of unknown to me.......

[budm]

Re: Short to ground on display board, how to find the culprit?

It seems to me that that output pin of the JF1 connector that goes to the blown inductor is probably for supplying the Voltage to the display board.
Please clean up the board so you can easily see the trace to find out how that inductor is connected in the circuit.
When you are saying shorted to ground, at which point on the board that is show 0 Ohms to GND?
BTW, so you have more than one of this board?

[WHaThEFLuX]

Re: Short to ground on display board, how to find the culprit?

Your first assumption is absolutely correct.

When I say shorted to ground, I mean that when I beep test from the ground plane to most other components on the board, it beeps. On a functioning board, all of these components do put out an Ohm reading when tested, but don't beep. When power is connected to the board it just about catches on fire around that black crater by the ground, leading me to believe that there is a direct short to ground there.

I have many of these boards at my disposal, attached is a picture of a working one. In most cases, the L7 inductor is the only component that is bad, replacing it makes the board function correctly.

[budm]

Re: Short to ground on display board, how to find the culprit?

What is the threshold of your meter when set to continuity test mode for it to beep? Most meter will beep with resistance as high as 50 Ohms. Using beeping mode to look for shorts is not valid, you need to check the resistance.

[stj]

Re: Short to ground on display board, how to find the culprit?

there is a via in the crater, you need to grind out all the carbon and then link anything that got cut.

[budm]

Re: Short to ground on display board, how to find the culprit?

So it looks like VCC plane supplies Q10 Collector is Voltage the supply for the L7, that VCC plane also goes to the two connectors' pin.
Pictures of the bottom side of the board?

[WHaThEFLuX]

Re: Short to ground on display board, how to find the culprit?

Not sure about the meter as it is a cheap one, I'm at work now but I will take a picture of the other side when I get home!

stj, how do you know there's a via in the crater? I've attempted to grind that spot out on other boards, it seems like there was copper there, not sure how I would figure out where it goes?

Thanks so much for all your help guys, I was about to give up on this but there might just be a way to repair it, I'm also not opposed to running jumper wires if need be.....

[R_J]

Re: Short to ground on display board, how to find the culprit?

Did this board get some water on it? it looks like it (white residue around JF1 pins) That could have started the arcing under the L7 coil, so once the carbon is removed it might be ok???

[budm]

Re: Short to ground on display board, how to find the culprit?

Not sure about the meter as it is a cheap one, I'm at work now but I will take a picture of the other side when I get home!

stj, how do you know there's a via in the crater? I've attempted to grind that spot out on other boards, it seems like there was copper there, not sure how I would figure out where it goes?

Thanks so much for all your help guys, I was about to give up on this but there might just be a way to repair it, I'm also not opposed to running jumper wires if need be.....

I don't think there is any VIA under that inductor, just remove the inductor and see.

[stj]

Re: Short to ground on display board, how to find the culprit?

directly right of the upper pad of L12
it's tiny, it could be a "hidden via"

[budm]

Re: Short to ground on display board, how to find the culprit?

I thought you are talking about there may be VIA under the L7, the VIA above L12 looks intact to me.

[stj]

Re: Short to ground on display board, how to find the culprit?

not above, directly to the right in the center of the crater - it may have been linking the upper missing pad.

[WHaThEFLuX]

Re: Short to ground on display board, how to find the culprit?

Here is the other side of the board.


I might be able to take a scrap board and scrape the solder mask away to see what's going on underneath that area, is that worth doing?

[R_J]

Re: Short to ground on display board, how to find the culprit?

it seems to be double side board, there might be a middle layer but I doubt it.
This looks like the ic and it is connected to the pzt2222at1 transistor.
I flipped the bottom view so it makes it easier to trace

[budm]

Re: Short to ground on display board, how to find the culprit?

I think the OP need to really verify the so called 'SHORTS' because the meter is beeping in continuity mode, it beeps does not means it is shorted.

[WHaThEFLuX]

Re: Short to ground on display board, how to find the culprit?

Bud, I apologize for my naivety, in my experience when damage occurs to that extent it is usually due to a short to ground, especially with the ground plane being right there......

On the working board, many of the components read OL on the meter when tested between them and the ground plane. On this board, literally half of the components show continuity to ground, indicating something is seriously wrong.

My expertise is extremely limited, if you could offer a theory as to why that is happening or what I can do to diagnose what's going on I'm all ears.

[budm]

Re: Short to ground on display board, how to find the culprit?

That board (Voltage supplier) looks to be supplying the Voltage through that inductor to the connector JF1 pin to the display board (the load), so when you have shorted load (shorted Diode on the display board as you had described), that inductor will blow up due to very high current flowing through it; the inductor can only handle current up to the limit of the spec.
Since you do have working set of board why don't you just check the DCV on that pin of the connector.
May be you should up load the pictures showing how all the boards are connected together and how the Power supply is connected to this device which we do not have have the make and model yet.