Smoke from the RCA connection! Did I ruin my board?

[telarium]

I was doing an experiment in trying to wire an RCA signal directly to the board instead of using a connection. I'm not sure what happened, but something went horribly wrong and smoke came out of a component near the RCA connection. I've illustrated where it came from in the attached photo.

Photo-Sep-01,-12-36-17-PM.jpg (56.86 KiB) Viewed 1852 times

The board still works... I think. I don't have an HDMI setup to test it with. Is there any way I can somehow bypass this component or repair it? Or will I have to get a new one?

[telarium]

Clearer photo attached.

[mahjongg]

I assume its D4, a double diode BAV99 that protects the broadcom's video output pin from becoming higher than 2.5Volt (The video DAC power supply voltage) or negative.

Burning this diode out can only mean that there have been dangerous voltage on the composite video cable. Perhaps your TV wasn't properly grounded, and the TV is leaking mains voltage to its low voltage internals, (or even its GND). Properly grounding the TV should help. If your TV doesn't have a ground pin on it power supply cable its probably a "double isolated device", which certainly shouldn't leak any dangerous voltages, which suggests its broken inside.

Alternatively its not the TV that is leaking the dangerous mains voltage, but it actually the PI's PSU that does it, and the TV is properly grounded, and acts as an exit path for the dangerous mains voltage on your PI.

Some very cheap chargers are actually dangerous, as this video shows.
http://www.youtube.com/watch?v=T88ej64aXUM&feature=plcp

safest thing to do is to replace D4 with another BAV99, after you have solved the problem, otherwise the next time more things may break than just D4.

[redhawk]

"trying to wire an RCA signal directly to the board" - are you trying to turn your PI into a video capture board??

Richard S.

[telarium]

No, I was just trying to create a permanent RCA connection between a TV and Pi.

BAV99 sounds like the way to do it... only question... how? It's a very small part, and it doesn't look like it can easily removed or replaced. Any tips?

[mahjongg]

Depends on what tools you got!

A professional would use a hot air soldering station to melt the solder the use a pair of pliers to lift off the BAV99, the he/she would clean the solder-pads with solder-wick (or a de-solder pump), then clean off the burned flux with cleaning fluid, then using either solder paste and hot air, or thin (0.2mm) solder (no lead free, but leaded "60/40" solder) with a resin core, and a needle point soldering iron, a pair of plier, a stereo microscope and a lot of patience.
Just to give you an idea what would normally be needed.

If you have none of that, cover the BAV99 with a big ball of molten solder, then carefully bang the side of the board on a table so that the molten solder together with the BAV99 fall off the board, then try as best as you can to solder a new BAV99 to the board, a pair of pliers and a table lens (such as stamp collectors use) is almost a prerequisite, unless you have very good eyesight, and a toothpick. If the point of your soldering iron is much too large try winding a paperclip around it, and use the end of the paperclip as your "solder tip". Before trying to use it, first tin it with your 60/40 solder, then wipe the solder off with a wet (natural) sponge, or wet toilet paper.

good luck.

P.S. obviously if the PI is still outputting a TV signal, chances are that the "burned out" BAV99 isn't a problem, and can remain in place. But you lost your protection. If you just extended the wire, you can also fake a BAV99 off-board using two standard (axial wire) diodes (1n4148's for example), see schematics for how to connect them.

[c.cam108]

If the point of your soldering iron is much too large try winding a paperclip around it, and use the end of the paperclip as your "solder tip".

This is an interesting suggestion - how well does it work? Does a paperclip take solder well?

[mahjongg]

Well, I did such a thing once, (actually I have succeeded in soldered a broken off wire to a DB-9 connector in a "wartel" {telephone shop} while on holiday in Java Indonesia, with a nail hammered in a piece of wood heated above a gas fire, but that is another story!) it depends on what the paperclip is made off what it is covered with (chromium would be very bad!) and how clean it is, perhaps you can sand paper it to get to the metal below the surface, and you should read "paperclip" loosely. Maybe thick solid copper wire is better suitable, if its strong enough to clamp around the soldertip. Actually the tip itself doesn't have to take solder, as long as it transfers heat effectively.