SMT Diode id & home automation system repair

[mypcbis$crewed]

oops, you are quite right...thats all I have left after 13 hour days
Yes, that battery is as you said 12v 7Ah. Perhaps tomorrow I will steal some time to perform the mentioned checks. I will write back with results soon! Thanks

 

[mypcbis$crewed]

Ok, I connected the keypad via jumper wires to the system and it temporarily powered up. I disconnected to make sure nothing was getting hot and when I reconnected the system seemed to reset itself so I disconnected the keypad again. I noticed that the second time the keypad in my hand did not light up. I can only conclude that the keypad is partially working because of the damaged diode? I believe that I will have to replace the diode first and then continue troubleshooting. I wasn't able to take any measurements on the keypad.

I tried to get current readings on the sounder, by likewise no luck with this vom. I wired it in series and double checked that the connections were good, even wiggled them

 

[Resqueline]

Busy week..
How about powering/testing the keypad straight from the battery to save the system? You'll have to make sure to hook it up right, or else.. Anything bad on it will surely smoke..
Tried checking for bad fuses in the vom? The Amp range is a pretty "exposed" part of any meter..

 

[mypcbis$crewed]

++ me too.... ugh too much this week

Genius as usual though, it was the fuse

I powered the unit using a 9 volt, however, the unit was drawing 2A and was not lighting up, the puffed diode was getting hot and I disconnected. I did notice that the diode was loose and of it came! I don't know if the heat lifted the trace or if it was loose from the first go.

There is continuity at the fringe of each pad with the negative battery terminal. I guess when I can get a replacement part I can solder it back on and try again. I don't have any bidirectional diodes on hand so I will have to wait a bit and ask a friend who tends to have a bunch of parts on hand.

 

[Resqueline]

Ho-ho, that's a deep-fried diode allright..
You can always try to power the panel w/o that diode, it's only there to protect against overvoltage. Just to see if there's something more wrong with the panel.
The pads came off with the diode, and I'd rather replace it with a higher-powered leaded device anyway - hooking it directly to the power pins on the plug on the board.

 

[mypcbis$crewed]

The unit works under battery power. Can you clarify what you mean by "hooking it directly to the power pins on the plug on the board" - are you saying to put it in series by cutting the negative pin? Can you make any recommendations? Wouldn't putting a higher value lessen my protection on the other components?

thanks!

 

[Resqueline]

Ok, good. The diode is connected from + to - on the board but those pads are damaged so instead just connect it straight onto the + & - pins on the PCB plug where the power comes in, no cutting. A higher power rating just means that in case of an overvoltage it won't fry and short out the power supply like this one did. It won't degrade any other properties of the system.

 

[mypcbis$crewed]

Understood. What is puzzling me is that the trace that is left on both sides of where the diode used to be reads continuity with the negative lead. Is this because it is passing through other areas of the board, thus misleading my readings? Or is this diode supposed to be in series with the negative lead only since it was a bi-directional diode. Also are you able to make a recommendation on what I should use in place of the diode (the higher value you spoke of). Thanks ever so much again

 

[Resqueline]

Only explanation I have is that you perhaps mistook the diode test "0" for 0 ohms? What was your favorite supplier again? I can look there for a suitable replacement.

 

[mypcbis$crewed]

I was able to track down a SA15CA (radial lead style), although its not an upgrade, it is very similar to the smbj15ca. Hopefully I will be able to pick it up tomorrow. I will let you know as soon as I get it and solder it on. Thanks

 

[mypcbis$crewed]

No dice, apparently they are just a distributor and even if you walk up to the door and ask to buy something, they have to mail it to you and charge you the s&h fee... its a 22 cent item to mail it for $6.95+ is ludicrous honestly.... some companies are just too big. I will continue to search out a local supplier if not I will have to just order it. Just seems like such a waste.

 

[Resqueline]

Yep, that sounds like an all too familiar - and growing problem.. :/ Good luck..

 

[mypcbis$crewed]

Yes...some are in business just to count their inventory instead of selling it
Anyways, I was able to obtain some data with my fixed VOM

With the existing wiring the horn draws 130mA when triggered and 120mA while sounding. (running off the battery)

The zones tallied up 100mA
The one console 40mA

All told with an extra console ~ 300mA the specs had figured no more than 570mA which is still under the 1A max the board can provide. So I am thinking I should be safe spec wise.
More troubleshooting on the keypad as soon as I get that diode secured. I think I will have to order it though

 

[(*steve*)]

Looking at the specs, a 15V zener may be a good temporary substitute. It looks like it's there to absorb transient spikes on your power supply (and to blow a fuse if the supply is connected the wrong way around).

 

[mypcbis$crewed]

Thanks Steve, a friend had an order going out and let me piggyback a few sa15ca's so I should have them at the beginning of next week
Will post again with the outcome.

 

[mypcbis$crewed]

I got the sa15ca diode and soldered it to the keypad. The keypad now no longer works! I think its the diode to be honest. I checked the spare one I ordered as well as the one I installed and they both have no values when I check them with the diode feature of my meter. Meanwhile the old diodes on the board have values. The new ones show no resistance, to clarify the meter doesn't register anything when I touch the probes to the leads of the new parts! I am confused. Help! Thank you

 

[Mitchekj]

I have to ask, forgive me...

You've installed it with the correct polarity? Also, when you read them with a meter, you SHOULD read an open (the meter doesn't do anything) when reverse biased, i.e. red lead on cathode, black lead on anode.

When you forward bias them (black on cathode, red on anode) you should read something like (Edit) 0.3 - 0.7V when in diode check mode, depending on the type.

 

[mypcbis$crewed]

No forgiveness necessary I didnt give you enough information! It's a bidirectional diode, so as far as I know, there is no polarity. I also did a search via google for the schematics of a bidirectional diode, trying to learn a little more about what happens in that "black box" but I wasn't able to find anything. Does anyone know how exactly a bidirectional diode works? To me, it would seem that no voltage would pass in either direction because there are two diodes wired in series but they are each in reverse to each other.

Here are some pics of the mess. This was accomplished with a fat tip on a radio shack iron so forgive the crudeness...I didn't even have my pliers handy...eek. FYI toe nail clippers work fine for cutting leads ;0 I verified with magnification that there are no shorts electrically, no solder bridging, the leads are not even touching the diode packaging.

 

[Mitchekj]

Oooh,. sorry, been a while since I read through this thread. (I guess I should've looked up that part number.)

A TVS diode, treat it almost like a zener. That guy should read as an open until you apply >= 15V to it. Then it will start to conduct. What kind of voltage are we talking about on those pins?
Edit: And hey, those joints don't look bad at all for a cheap iron! Nicely done.

And it's not exactly two diodes in series, reverse of eachother... it's two zener diodes in series, reverse of eachother. While one is forward biased, and passes current normally, the other goes into avalanche mode at a certain voltage and passes current.

 

[Resqueline]

Mitch got it right there.
I can't say why the panel would stop working with that diode in place.
Try to measure some ohms and voltages on the connectors, see if there's any breaks or shorts somewhere.