TV Manufacturing Question

[fsleeman]

I was recently given a broken 32" Vizio TV that apparently just cut out and never worked since. I have purchased a service manual and looked inside but haven't found anything obviously wrong with it.

One interesting thing I noticed was how some of the capacitors were soldered. Most of the through hole components have a nice solder bump on the top and bottom of the board, but a number of the capacitors did not. All of them had plenty of solder on the back but for many the solder stopped well below the top surface of PCB. In some cases there were two capacitors next to each other with the exact same numbers, one had full solder and the other didn't. Is this a manufacturing defect or is it some clever trick? The capacitors were silk screened with a circle half clear, half white (the quesiontable solder side). It looks like these capacitors are using vias instead of surface traces.

Another thing I didn't understand was why most for the capacitors were offset from the PCB by a good 1/8" inch instead of being flush (which why I can see the solder so well). Wouldn't that make it much more likely for these to get knocked loose? I don't know a lot about consumer electronics so I don't what is normal. Thanks.

[Zero999]

IT sounds pretty normal to me, there might be a few bad connections but it's difficult to know without a clear photograph of the board.

Capacitors should not be mounted flush, there should be a small gap because it makes them less susceptible to damage when soldering.

[qno]

They should however be fixed with a blob of glue.
To prevent them breaking during vibration.
There are IPC norms for this I do not remember exactly bu t I think IPC-620.

[fsleeman]

IT sounds pretty normal to me, there might be a few bad connections but it's difficult to know without a clear photograph of the board.

Capacitors should not be mounted flush, there should be a small gap because it makes them less susceptible to damage when soldering.

I understand not wanting to make the caps flush, but these looks pretty high off the board. I will see if I can post a picture.

[Zero999]

It depends on the size of the capacitors, it's more important to secure lage capacitors than small capacitors.

[fsleeman]

Here is picture of what I was talking about:
http://img34.imageshack.us/img34/1421/capsrq.jpg

The right pin had solder that goes slightly above the PCB, the left pin's solder does not even the reach top of the via, hence not shine.

[Zero999]

That looks pretty normal to me.

The holes are through plated so the solder is sucked into them by capillary action.

[fsleeman]

Ahh, too bad. Strange it only seems to happen on the white silk screen side of the capacitors.