Rectifier diode burned out?

Thread Starter

ko0bf4c3

Joined May 18, 2015
7
Hi peeps just looking for some advice really. My dad bought an android TV Box and it came with a foreign adapter. Instead of getting a UK plug one he just plugged another adapter in that had a higher voltage and it's fried what looks like a diode on the board. He's gave me the device now and I'm just wondering if I could be in with a chance of fixing it, the only problem is I'm not sure which diode I'd need to solder onto the board. I have found a few on ebay but not sure if they would be the correct ones to use.

The box's adapter had a power rating of 5V 2 Amps. Here are some pics below.





Any advice on this would be great thanks people.

Dan :)
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
I am guessing any general purpose rectifier should work, a SMT version of the 1n4000 series .
Or even a leaded version.
Max.
 

JWHassler

Joined Sep 25, 2013
273
If you are really lucky, that might be a diode whose only purpose is to prevent over-/reverse-voltage form toasting the device.
With little (or actually, in my case, nothing) to lose, I'd try a 2-amp+/10v+ Schottky diode.
 

Thread Starter

ko0bf4c3

Joined May 18, 2015
7
Thanks for the replies MaxHeadroom & JWHassler I appreciate it. I had found these ones.. I wont post links as I'm not sure if I'm allowed but this is the description [ 50 Pcs Through Hole 1N 4001 Standard Rectifier Diode 1A 50V ] - they are only 99p but up on seeing the 2A+ post am I best going for that as a minimum? The 2A ones on ebay are 2A 1000V and such.

Cheers. :)
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
In that kind of application I cannot see any more needed, any of the 1n4000 series (1n4007) would most likely work, and makes it a little more universally useful to have on hand.
Max.
 

Thread Starter

ko0bf4c3

Joined May 18, 2015
7
Thankyou Max I will order some & a UK adapter and have a go, fingers crossed it will work.

Dan.
 

ian field

Joined Oct 27, 2012
6,543
If you are really lucky, that might be a diode whose only purpose is to prevent over-/reverse-voltage form toasting the device.
With little (or actually, in my case, nothing) to lose, I'd try a 2-amp+/10v+ Schottky diode.
My guess would be a reverse polarity clamp diode, if it remained electrically continuous it probably did its job - if the diode blew apart before killing the adaptor, its probably landfill.
 

Thread Starter

ko0bf4c3

Joined May 18, 2015
7
Thanks for the replies guys. :)

My guess would be a reverse polarity clamp diode, if it remained electrically continuous it probably did its job - if the diode blew apart before killing the adaptor, its probably landfill.
AFAIK the adapter was fine after, he just plugged one that was too powerful into the box and smelt a burning smell and unplugged it straight away and that was the result in the pic, the rest of the board looks fine though.

is it a freeview box, whats the model number .
Nah mate its an android tv box. Model number CS918. :)

I have found another image of the board in it with the diode thats blown on mine. Not sure if you guys can make anything of it, it seems to have markings on the top.



Thanks peeps, Dan.
 

ian field

Joined Oct 27, 2012
6,543
Thanks for the replies guys. :)



AFAIK the adapter was fine after, he just plugged one that was too powerful into the box and smelt a burning smell and unplugged it straight away and that was the result in the pic, the rest of the board looks fine though.




Thanks peeps, Dan.
In normal use a silicon diode will clamp at 0.7V and a Shottky diode should clamp at least lower than 0.5V - but they do have some dynamic resistance (same sort of thing as a zener) so the fault current could have reached a volt or more, which is out of spec on the absolute maximum ratings for most chips.

Normally in this situation the protection diode will fail short circuit, and if you'relucky - save everything else. If it fractured and failed open circuit - it didn't protect anything!
 

ian field

Joined Oct 27, 2012
6,543
it maybe a zener diode, have you tried powering it up again with the correct adapter?
The TS posted a picture of a well cremated device - if it did the job it was supposed to, its now a dead short.

In the 80/90s some TV set makers used a protection zener (about 130V ish) on the HT rail, it was designed to fail short circuit if the HT went out of control. I havent seen zeners used for that purpose in any other equipment, but some items are protected by sidacs.
 

Thread Starter

ko0bf4c3

Joined May 18, 2015
7
In normal use a silicon diode will clamp at 0.7V and a Shottky diode should clamp at least lower than 0.5V - but they do have some dynamic resistance (same sort of thing as a zener) so the fault current could have reached a volt or more, which is out of spec on the absolute maximum ratings for most chips.

Normally in this situation the protection diode will fail short circuit, and if you'relucky - save everything else. If it fractured and failed open circuit - it didn't protect anything!
I'm not too clued up on diodes and such, I'm just looking at getting into soldering and wondered if this would be a easyish DIY job to fix. It it looking though its a no go though?

Cheers Ian :)
 

ian field

Joined Oct 27, 2012
6,543
What you could try is remove what's left of that part and make absolutely certan you only conect the right adaptor - as there will be no protection.

Check the polarity of any voltage that appears across the diode pads, if the cathode pad is positive; its a reverse protection shunt and if you device is going to work, it should be doing so.
 

Thread Starter

ko0bf4c3

Joined May 18, 2015
7
Just an update I bought a proper adapter for it but no joy, i removed as much as I could of the burnt chip aswell so it can't of been a protection diode? I notice aswell when I plugin the HDMI and then the power supply my TV detects the HDMI lead but no signal on TV, i've plugged in a USB root hub to the box's USB port and that lights up so there must be power passing through the box but theres no power light on the off/on button or any sign of it booting.
 
Last edited:

ian field

Joined Oct 27, 2012
6,543
Just an update I bought a proper adapter for it but no joy, i removed as much as I could of the burnt chip aswell so it can't of been a protection diode? I notice aswell when I plugin the HDMI and then the power supply my TV detects the HDMI lead but no signal on TV, i've plugged in a USB root hub to the box's USB port and that lights up so there must be power passing through the box but theres no power light on the off/on button or any sign of it booting.
Did you do the tests I suggested?

If its a series feed protection diode, you'll probably find a positive voltage on the anode pad - but this diode wouldn't burn up because of wrong polarity.

If there's positive voltage on the cathode pad, its most likely a shunt diode - if the device doesn't work with the remains of that diode removed, its probably toast.
 

Thread Starter

ko0bf4c3

Joined May 18, 2015
7
Did you do the tests I suggested?

If its a series feed protection diode, you'll probably find a positive voltage on the anode pad - but this diode wouldn't burn up because of wrong polarity.

If there's positive voltage on the cathode pad, its most likely a shunt diode - if the device doesn't work with the remains of that diode removed, its probably toast.
Hi Ian I don't have a tester or anything to test the pads I'm afraid, I was just hoping it would be a simple diode fix but I guess not lol. Just found it weird how power is going through the unit some way as it gets warm etc but theres no power lights or signal sent to the tv, just the tv detecting something is plugged in. It was worth a try I suppose.

Thanks :)

Dan.
 

ian field

Joined Oct 27, 2012
6,543
Hi Ian I don't have a tester or anything to test the pads I'm afraid, I was just hoping it would be a simple diode fix but I guess not lol. Just found it weird how power is going through the unit some way as it gets warm etc but theres no power lights or signal sent to the tv, just the tv detecting something is plugged in. It was worth a try I suppose.

Thanks :)

Dan.
You could use a red LED with about 330R in series to limit the current, should be OK up to about 12V.

The cathode is usually marked by a flat edge on the ridge around the bottom of the encapsulation, when cathode is most negative it should light.
 
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