Thread: RCA main board
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Default RCA main board

On Tuesday, March 16, 2021 at 7:25:57 PM UTC-4, Stu jaxon wrote:

I'm reading a short across both sides of the fuse 3a/125v to ground, on the tcon board, there's short somewhere.???
With the LVDS cable disconnected, you should not be getting any low resistance to the ground screws of the TCON. If so, there's a short. The most common reason for a dead short on a TCON are one of the multi layer chip capacitors (they're surface mounted and have no markings). While any dead short is easy to find with an ohm meter, these caps are usually found in groups of two to ten or more all paralleled, so one shorted cap makes them all look bad. Other than a Huntron, the easiest way to find this is to feed a limited current (2 amps tops) into the short with a variable supply and spray the board with freeze spray until the board frosts over. The first cap to thaw is the shorted one.
Extremely clever, and useful. Will have to file this trick away.
I usually do hunting by keeping the board powered up for a bit then spray targeted components.

That works if the supply maintains the struggle of feeding the short, but most of these more recent circuits (like these TCONs) are fed by buck converters who shutdown when the programmed current value is reached, so the offending load part never gets hot. When using the forced current trick, one must remember to limit the voltage, as sometimes the shorted part may suddenly open under the strain and an over-voltage will then damage something else.

I have a variable ps, and medical freeze spray, but i never injected a voltage/current into a circuit. could use some tips/pointers.??

Simply feed 2 amps (but no more) on either side of the fuse with respect to ground (the screw lands are fine). Since the input to the TCON is 12V, make sure your supply does't go over 10V or so. With a dead short, you should be reading mostly current and almost no voltage. Spray the whole board with freeze spray so it frosts over. Watch what thaws first. Could be one of the brown chip caps or even one of the chips.