Sanyo DP42740 Short on Main Board?

[caphair]

Have this Sanyo plasma Tv that once plugged in, the standby clicks on then quickly powers off.

With main board removed I have steady 5vsb so I start probing around and on two test points for 1.8v and 1v they measure shorty to ground.

I desoldered one cap on the 1.8v line and cap measures fine out of circuit so I soldered in two wires in its place hooked up an external power source and it drew 2amps. Felt around and the only component that got warm was the processor that I'm pointing to in the pic.

Does it mean it's shorted or something else possibly in line causing it to get warm?

[CapLeaker]

Re: Sanyo DP42740 Short on Main Board?

Did it get hit by lightning? You could somehow cut the trace near the IC or take the IC off then feed it power again. Other than that, you would need a very sensitive ohm meter in order to find that short and it is hard to do without proper equipment unless you check every single component on that rail. SMD chip caps fail short for example.

[caphair]

Re: Sanyo DP42740 Short on Main Board?

Not sure if it was hit by lightning. Someone in my building asked if I'd look at it.

I ended up soldering it off board using hot air (it was a pain)

Fed power again and there was very minimal amp draw around 100ma. So confirmed it but what's odd is the point I soldered in wires to feed power they still measures shorted

[CapLeaker]

Re: Sanyo DP42740 Short on Main Board?

weird. what about that IC right under the HDMI sockets?

[caphair]

Re: Sanyo DP42740 Short on Main Board?

That never got warm initially

[CapLeaker]

Re: Sanyo DP42740 Short on Main Board?

Regardless, the IC shouldn't be drawing 2A when it is off. Did the LED light up in front of the TV?

Anyway... got to get going for tonight...

[dick_barton]

Re: Sanyo DP42740 Short on Main Board?

You have as short cuircuit on your board. Possibly at the point supplying the 1.8V & 1V i.e. a regulator gone short cuircuit and not the large chip.
Do you have the manual?

Edit
Manual http://www.manualslib.com/download/1...o-Dp42740.html

[dick_barton]

Re: Sanyo DP42740 Short on Main Board?

I would check the regulators which supply the 1.8 & 1.1V supply

[caphair]

Re: Sanyo DP42740 Short on Main Board?

Those were the first things I removed but it still drew 2amps it wasn't until I removed the big chip that it stopped. Wouldn't that confirm the regulators are good?

[dick_barton]

Re: Sanyo DP42740 Short on Main Board?

Sorry but I must have misread your previous post. I thought you said you still had a short when you connected the wires back where the capacitor was located after you remove the large chip.

[dick_barton]

Re: Sanyo DP42740 Short on Main Board?

Have you checked the voltages on the regulators since removing the chip?

[caphair]

Re: Sanyo DP42740 Short on Main Board?

Yes I still measure short across the cap I removed. Not sure if maybe there's an inductor in parallel causing that because the 2 amp draw is completely gone? I haven't checked the voltages on the regulators

[caphair]

Re: Sanyo DP42740 Short on Main Board?

So I bought another mainboard off eBay and I have the same issue. Every other board tests fine. I noticed only voltage I don't have on the mainboard when powering on is for audio circuit. But I can't figure out how to troubleshoot it

I have 3.3v to the ic but I can't see where the + on c017 comes from and that's what's missing

[caphair]

Re: Sanyo DP42740 Short on Main Board?

Correction: I have all the 3.3v to the ic but nothing out of its vcc1 and vcc2 pins which is what provides audio power. Safe to say the ic is bad?

[dick_barton]

Re: Sanyo DP42740 Short on Main Board?

Nothing comes out of the VCC1 or VCC2 pins. It looks like 15V from the power supply feeds those two points from K8B pins 12 &13 as shown on page 23 of the above manual.

[caphair]

Re: Sanyo DP42740 Short on Main Board?

Nothing comes out of the VCC1 or VCC2 pins. It looks like 15V from the power supply feeds those two points from K8B pins 12 &13 as shown on page 23 of the above manual.

Makes sense. Thanks for pointing that out. I traced that line and it goes just through few inductors and resistors. All measure fine. Wondering now if the psu 15v line is the issue when loaded. I turned the psu on with everything disconnected and all voltages tested steady so I'm stumped

[CapLeaker]

Re: Sanyo DP42740 Short on Main Board?

maybe one or more of the caps from c017 is shorted to GND? Like C020 to C023...
Unplug the board and measure the resistance.

[caphair]

Re: Sanyo DP42740 Short on Main Board?

maybe one or more of the caps from c017 is shorted to GND? Like C020 to C023...
Unplug the board and measure the resistance.

First thing I checked. I don't know what else to look for? I have the 15v from the psu when I turn it on and heck before it powers off I see it momentarily but I don't see the same 15 at the audio power test point when I make same test

[dick_barton]

Re: Sanyo DP42740 Short on Main Board?

Have you checked if there is a short circuit from VCC1 & VCC2 to 0v on the audio chip itself. There is every possibility that it may have an internal short or low resistance to ground.
If there is a short, can you isolate the track carrying the 15V to VCC1 & 2 using a sharp scalpel to verify if it is the chip or lift the chip?

[caphair]

Re: Sanyo DP42740 Short on Main Board?

Have you checked if there is a short circuit from VCC1 & VCC2 to 0v on the audio chip itself. There is every possibility that it may have an internal short or low resistance to ground.
If there is a short, can you isolate the track carrying the 15V to VCC1 & 2 using a sharp scalpel to verify if it is the chip or lift the chip?

I measured resistance to ground of both vcc1 and vcc2 pins. Did not read shorted.

Oddly yesterday the 15v was there and tv powered up but there wasn't a picture then would cycle off and back on. Would stay on for 15 seconds then off and quickly back on.

Today I'm back to original problem of it quickly turning off when powered on