PCB "noise"

Timsmith

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Hi,

I just bought a jamma board (Robocop) to swap with my Superman board. Superman works fine. Robocop on the other hand has a strange thing happen:

1) The power supply makes a buzzing noise
2) The picture has a little noise
3) The sound has a little crackling

However, after 5 minutes or so, the problems go away.

Is it bad capacitors on the board? Should I try reflowing solder to the capacitors?

My knowledge is very limited so I'd appreciate any help,
Tim
 
Maybe a Cap on the 5 or 12 volt line. Or you have a colder solder or a going bad lead internal to one of the transistors or IC's. The part(s) are making just enough contact to work but because of the poor connection the part(s) draw more current until the joint heats up and the electroncis can now flow more easely.

Try using freeze mist in isolated spots and see if you can duplicate the problem.

RJ
 
Try using freeze mist in isolated spots and see if you can duplicate the problem.

Thanks RJ. Can you explain the freeze mist technique? Once it's running well start freezing components one at a time?
 
Freeze mist.

You can pick up a can from Radio Schack.
Take a look at the schematic of the board. See if there are any regulator chips etc.

When the board stablizes you can spray a suspected componet and recreate a cold componet. it can be deceptive because some of the componets do not like the cold to begin with. and will cause the game to act iratic.
I use a small amount on a suspected component and wipe the board off after each try with a cloth.

Sometimes I just use the cold air from a hair dryer.

And since it is cold out and we have plenty of snow in Chicago you can allways use the
small amount of snow in a zip lock bag with a piece of paper towel around it and hold it against a suspected componet. Saves you from a wet freeze misted board.

The componet in question is on the edge from room tempature to operating tempature with current flowing threw it, that is causing your problem. Check and see if any componets are becoming overly hot. Sometimes you stumble on the weak connection internal to the IC or transistor.

It can be a slow process. I put the board in sections with magic marker marks on the edge and go threw the chips and transistors in that section. sometimes the diodes at the end.

And there there is the ...Change out the power supply and see were that gets you.................. same holds true for power supplies.

RJ
 
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