PCB Tracing

Thread Starter

shashankrevankar

Joined Sep 1, 2011
10
Hi,

I have PCB of my home theater system which has gone bad.
The problem is that the voltage & ground traces on the pcb have been shorted due to some faulty component.

I am not able to trace out the component which is causing the short. I tried the rectifier IC but it turned out to be working fine. Other things on the power PCB section are a voltage regulator, some capacitors & resistors.

Does anyone know any device or technique to find the faulty component?
Please help me.
Thanks
 

bwana

Joined Sep 1, 2011
2
Pretty sure the short isn't in your power section.
Try cutting (in a way you can then restore) at least the power trace exiting the power section. If the short is on the power you'll have yet no power out, otherwise you'd see it.
Same way if you have power: identify all power connections in the remaining circuit and possibly unsolder (or cut) their connections without resoldering until you have no more short.
Good luck!
 

Thread Starter

shashankrevankar

Joined Sep 1, 2011
10
Pretty sure the short isn't in your power section.
Try cutting (in a way you can then restore) at least the power trace exiting the power section. If the short is on the power you'll have yet no power out, otherwise you'd see it.
Same way if you have power: identify all power connections in the remaining circuit and possibly unsolder (or cut) their connections without resoldering until you have no more short.
Good luck!
I had taken the pcb to an experienced guy, he told me that problem is in power section bcoz the fuse in power section blows out immediately after connecting.

Also the PCB is very complicated and I am afraid to try desoldering and soldering. (I will do it if thats the last resort). Please tel me if u have any other method.

Thanks :)
 

suds

Joined Apr 28, 2009
4
Fuse blowing issue come when, one or all of them due to surge goes bad..

Thermistor,Capacitor,Bridge rectifier/Diode,filter capacitor, Switching transsitor(internally short).

can you post schematic, image of power supply both sides.. ?


@Shashank (where are you from , I am at Bangalore)
 

Thread Starter

shashankrevankar

Joined Sep 1, 2011
10
Fuse blowing issue come when, one or all of them due to surge goes bad..

Thermistor,Capacitor,Bridge rectifier/Diode,filter capacitor, Switching transsitor(internally short).

can you post schematic, image of power supply both sides.. ?


@Shashank (where are you from , I am at Bangalore)
@suds I am at Hubli,

I will post the image. I dont have a schematic as it is a company product and they dont provide it.
 

John P

Joined Oct 14, 2008
1,762
Well, here's a method, but it's better for finding shorts on a blank board than a fully populated one.

Apply some known current to the shorted circuit. The more the better, but it has to depend on the components you've got installed.

Put one probe of a voltmeter on the low side of the power supply where the feed to the board is connected (probably the ground trace). Then measure the voltage at different points along the trace. If you keep measuring a higher voltage, you're on the way to the short; if it stays the same, you're following a dead end. When you find the highest voltage on what's nominally the ground trace, you've reached the goal. But if your board has ground and power planes, I doubt if this method will work.
 

fddizon

Joined Dec 4, 2011
1
Hi,

replace fuse with a 100 watts light bulb to prevent blowing up fuses and do John P's method to locate the shorted component.
 

Adjuster

Joined Dec 26, 2010
2,148
The last but one post on this thread was months ago. By now the OP has most likely given up on this thing, or possibly he now has it fixed.
 

MrChips

Joined Oct 2, 2009
19,384
A current probe is used to locate shorts across supply lines. You inject a current pulse and trace where the current goes. Most times the culprit is a shorted bypass capacitor.
 

Thread Starter

shashankrevankar

Joined Sep 1, 2011
10
It looks like you have a burned-up trace next to the 9v regulator.

Why not post a more detailed photo of that area?
Yes, I did that long back.
I replaced the 9V regulator with a new one.
The fuse did not blow out now :))

Now I have a different kind of problem. :((

When I switch on the power now, I get a loud humming sound from the subwoofer. Still there is now audio output.

This was the problem I had in the beginning, i.e loud humming. A few times I tried to test the speakers with this loud hum present and then the problem of fuse blowing out started.

Now I am afraid the fuse would blow out again!!! A local technician told me that the amp IC must have blown up inside..
 

MrChips

Joined Oct 2, 2009
19,384
Hang in there. Don't despair!
We got guys on this site who can fix boards by just looking at them.
What electronics experience do you have?
What test equipment do you have?

First things. Don't apply power any more. We don't want to make matters worse.
Also in future, disconnect the speakers before doing any further testing. You could blow the speakers.
 

Thread Starter

shashankrevankar

Joined Sep 1, 2011
10
Hang in there. Don't despair!
We got guys on this site who can fix boards by just looking at them.
What electronics experience do you have?
What test equipment do you have?

First things. Don't apply power any more. We don't want to make matters worse.
Also in future, disconnect the speakers before doing any further testing. You could blow the speakers.
Hey MrChips. Thanks. I have quite a bit of experience in handling electronics as I am in 7th semester of Electronics Engineering.
Also I have made few PCBs myself, so soldering wont be a problem as long as they are not SMDs.

Now I have completely removed the connections. Only the amp is active now.
 

MrChips

Joined Oct 2, 2009
19,384
What test instruments do you have? DVM? Scope? Current Probe?

Are you saying that the amp is no longer blowing fuses?
 

Thread Starter

shashankrevankar

Joined Sep 1, 2011
10
What test instruments do you have? DVM? Scope? Current Probe?

Are you saying that the amp is no longer blowing fuses?
Yes I have a DVM, Scope can be arranged easily. I dont have a current probe though. I wil try to get one immediately.

Yes the amp is no longer blowing fuses.
 

MrChips

Joined Oct 2, 2009
19,384
Yes I have a DVM, Scope can be arranged easily. I dont have a current probe though. I wil try to get one immediately.

Yes the amp is no longer blowing fuses.
Don't worry with the current probe.
The current probe I am referring to is a special one only made by HP.
If you're not blowing fuses then we're ok to trouble shoot.

I have to go so I'm roger and out.
 
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