Yellow Gunk - Is It a Leaking Capacitor or Strain Relief Goop?

What your are seeing is most likely the assembly glue. During the assembly run, some of the components have to be glued down in to place so that they do not displace when the board passes through the soldering bath.

Most of the time, bad capacitors are not visibly bad. Leaky capacitor, means that the cap is becoming resistive internally. This would be in effect, "resistance leakage". To properly test caps, you need an ESR meter to start with. A capacitor meter is also good to know if the uF value is correct.

There are many more types of failures that can occur to make a power supply fail than just capacitors. Without the proper training, service information (service manual), and test equipment, the power supply will probably not be possible to repair unless you would know the exact parts to change.

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JANA _____

It will be two years old next month.

It seems to have a power supply problem that is similar to what others have reported, and is likely due to a bad electrolytic capacitor.

The symptom is:

The unit is in standby mode, with a red LED lit, as it is supposed to be.

Pressing the power-on button causes the red LED to turn off - as it is supposed to - but nothing else happens. After a few seconds, the red LED comes back on as though the power-on button had never been pressed.

Pressing and holding for a few seconds the power-on button makes the unit seem to come to life and operate normally. No need to hold down the power-on button.

The unit seems to function normally until it is shut off (into standby mode), and the the same symptoms happen when I try to power it up again.

So far I have opened up the unit and removed the power supply.

No capacitors look to be bulging.

There is some rubbery pale-yellow stuff that seems to have been spread deliberately on the circuit board, near one of the capacitors, but especially along where a 7 conductor ribbon cable enters the circuit board.

Is this the leaky stuff that some have called "yellow gunk" from a split open capacitor? I picked at the stuff, and it is definitely *rubbery* and not all all liquid.

Or is this some stuff that is meant to be a strain relief from the ribbon cable to the PC board?

Does anyone know where to obtain a schematic at least for the power supply? It would help to at least identify the caps on this board. Any constructive suggestions?

A related question: If I parallel a pair of capacitors to get close to the needed value, do the bodies of the two caps have to be insulated or separated from each other?

--- Joe

I repair many DVD players during the course of my working life, and the symptoms that you relate, are pretty typical of bad caps. As JANA said, the yellow gunk is almost certainly there deliberately as either strain relief for the wires that you mention, or for the caps themselves. Also, as he says, there is no substitute for an ESR meter when looking for bad caps. A capacitance meter is of limited use in this instance. Many is the time that I have removed bad, but perfectly serviceable *looking* caps, which have had an ESR reading that is away with the fairies, but whose capacitance value is spot on.

The bad cap(s), if indeed that's what the problem is, is likely to be a small one on the primary side - typical value 1uF to 47uF, and possibly located near to some other component that runs hot, such as the main switching element, and its heatsink. You could also have a secondary-side cap causing it, but most often, when one of these is to blame, it can be seen to be bulging. If you have a 'scope, you can look for HF ripple on the secondary rails. Another way that you might get to the bottom of the problem, is by using a can of freezer, and a piece of cardboard to confine the spray to specific components. If you have a decent can, you can get single drips of freezer from it. Also, take the time to look around the rest of the machine to see if you can spot any 'distressed' looking caps elsewhere, or any located close to hot areas. Sometimes, the type of shutdown that you are seeing, is caused by poor caps off the power supply.

As to your question regarding paralleling caps up, there should not be any need to insulate the bodies, as they are usually pretty well insulated in the first place, and even if not, the 'can' is invariably the "-" terminal, if it is commoned at all. In general, I would not recommend this approach when dealing with switchers. Electrolytic caps are 'poor' things in terms of construction and stability, and work in filter applications by the 'shotgun' principle. There is no guarantee that two caps in parallel, even if they come from the same manufacturer and series, will have the same inductance as a single cap of the right value, nor that the high frequency current that they are filtering, will divide equally between them. All caps used in switchers are usually pretty easily available, and you should replace them with low ESR 105 deg types, specified for this application. Switchers are pretty fickle things, and it doesn't take a lot to upset them, sometimes with catastophic (literally) results. Best not to mess with the way that the designer specced his parts in the first place.

And if you're not familiar with working on switchers, PLEASE TAKE CARE. They can be lethal. And I mean that totally literally, as in dead ... If you have an isolation transformer available, it should at least be connected to this, whilst the covers are off.

Arfa