Console Motherboard Circuit Question

[tjerkotten]

Hi, I am new on this forum, but I hope to learn more about this. I am working for the last 1,5 years with Motherboards of an old game console, the Dreamcast. Sometimes I have faulty motherboards. I replace the capacitors if needed and hope I can get it up and running again. I am currently working with a board that has a problem I can't seem to understand.

One of the capacitors seemed faulty. When I checked it with my multimeter, it had a continues beep, where it should be a short beep for good capacitors. I removed the 100uf 16V SMD capacitor and check it on it's own. It has the continues beep, so I replaced the capacitor with a new one, but still it would give me the continues beep when on the board.

I removed the capacitor again and check the pads itself on the board without the capacitor on. It also gives a continues beep, where it should be short. Is there something wrong with the circuit? Could someone give me some more information on this?

Thank you very much in advance. In this picture the pads aren't cleaned fully yet.

 

[Nigel Goodwin]

Simple, there's a short somewhere else on the board - it's VERY common for there to be multiple decoupling capacitors on supply rails, and quite common for multiple ones to fail.

A good way to fault find these kinds of faults is to use a very low-ohm resistance meter as this will even measure the resistance of the tracks - so measuring across the one you've replaced might read something like 0.1 ohms, but measuring across the faulty on might only read 0.01 ohms, the extra resistance is that of the track.

Here's one a friend of mine built and uses.