surface mount device codes

Posted on 2015-01-07
Last Modified: 2015-01-16
has any body got any idea what a surface mount device is with marking GFN 38 and also a diode symbol with its legs wrapped around to form a capital S. the device is 7mm long 5.5 mm wide and 2 mm deep, the two connections are on the short ends. it measures 4 ohms. It is in a dog perimeter minder circuit board , no bar marking on either end . just the symbol and text . the low value of ohms is causing over current draw on the 12 volt supply . i have extensive google search with  no success . removing the device from the board has solved the problem and it appears to work correctly . but mave not tried it with the dog collar.
Thanks for assistance in advance.
Question by:TopTed
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LVL 27

Expert Comment

ID: 40537028
Presumably the circuit was working, then it stopped working, and you noticed the suspect part was getting hot.  I think what you have is a failed protection diode.  The circuit will work fine without it, but it will be at increased risk of damage from line voltage surges.
LVL 48

Expert Comment

ID: 40537126
I believe FN means Flat No-Lead.

However I can't get any further than that.
LVL 27

Accepted Solution

d-glitch earned 500 total points
ID: 40537875
A close-up photo of the circuit, suspect part, and logo could help a lot.  
There are dozens (if not hundreds) of possible manufacturers and many thousands of possible part numbers.

I believe the part is something like one of these:
Bipolar protection devices would not require an indicator band.
The suspect device probably wouldn't have measured 4 ohms when it was new and working.
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Author Comment

ID: 40539947
LVL 27

Expert Comment

ID: 40539969
Thanks.  That isn't the official logo for ST, but they would probably be irked if another company used that mark.
I'll resume the search there.

Author Comment

ID: 40550609
If there is no further comment , i think i will put it back into service and hope there are no surges. thanks for looking , I have had no further success either.
LVL 27

Expert Comment

ID: 40551270
I have looked at the ST website and found more than a hundred of these parts with 3-letter codes, but none of them is a match for yours.  Some of the relevant data sheets are attached.  The 3-letter codes are on page 8.  The middle letter is always U or B (for unipolar and bipolar).  And the logo looks different too.

Author Closing Comment

ID: 40554859
I chose one of the vishay bidirectional devices as they were the same dimensins . i have put it in the pcb  and returned it to the customer and it is working ok. Thanks

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