To Test a PCB with alot of HIDDENED SHORTS

[walters]

To Test a PCB with alot of ""HIDDENED SHORTS""

1.) Bench power supply, use it as a current source only , turn the voltage down all the way, and turn up the current knob on the power supply to about 100mA or more .

2.) What else can you use as a current source?

3.) Put the current source ( RED probe ) on node#1 input of first stage and the current source ( Black probe) on node#2 of the output of first stage, so it makes a "current loop"

4.) Take your DVM meter and measure the voltages of each node in that faulty stage until you get a low voltage drop reading on a node or pin.

5.) Once you "isolated" the two nodes that get a low voltage drop, put the current source RED probe and Black probe on the two nodes and measure across them to find a voltage drop which will be the "hidden short" inbetween the traces or between the nodes

6.) A short has current flow but NOT a voltage drop

How does this sound ?

 

[FvM]

Yes, that's basically the method I meant as I previously suggested using a "current limited low voltage" to locate shorts. To protect the board and devices, it's important to prevent from inrush currents by using a low voltage setting in addition to set a suitable current limit. You should check, that the power supply is capable of a stable current limited mode.

With multiple shorts at a power net or shorts on power planes, the method may be unable to locate shorts.

 

[walters]

current limited low voltage" to locate shorts, explain more please?

Whats a current limited low voltage?

power supply is capable of a stable current limited mode.

I never seen a power supply with currrent limited MODE? whats that?

With multiple shorts at a power net or shorts on power planes, the method may be unable to locate shorts.

Why is that? please explain?

 

[wolly]

multiple shorts at a power net or shorts on power planes, the method may be unable to locate shorts

this procedure is unable to detect shorts in multi layered board having power planes in the inner layers

 

[walters]

this procedure is unable to detect shorts in multi layered board having power planes in the inner layers

How would you detect these type of shorts on multi layer boards?